Diagnosing a damaged cylinder head gasket

[Sharky]

My car has been suffering from overheating under high load. I suspect that it might be an electrical problem, particularly with the fan as I think that instead of engaging second speed it might be shutting down. However, my mechanic believes that the cause could be a "burned" cylinder head hasket. However I wouldn't like to dimount half the engine just to find that it was OK so he told me that there are a couple of ways to tell if there's any damage. First is to open the expansion bottle when the engine is cold (preferably during the mornings) and see if there's any air going in or out (like when one opens a soda bottle). Number 2 to check for traces of moisture on the oil cap. I've done both but both tests have yielded no indications of a bad gasket.

Is there anything else that I could do diagnose it?

[thebear]

Originally Posted by Sharky

Is there anything else that I could do diagnose it?

Lots of things:

The thermostat could be frozen partialy closed. With a thermometer, verify the temperature on a metal part of the radiator housing. This will also give you an indication of the effectiveness of the fan control switch as you can observe the temperture rise to the operating point(s) for the fan(s). Check a service manual. Usual range is 110-125° C. The top of the radiator will be the warmest, the bottom will be the coolest. The sensor is usually placed near the bottom of the radiator. When (if) the thermostat opens, the temperature should decrease by at least 10° C within a few minutes. If not, spray cold water from a hose on the front of the radiator (careful not to flood anything in the engine compartment).

The timing could be retarded or the spark plugs could be deteriorated so as to provide late/difficult ignition.

Fuel mixture could be too lean under load. You didn't state if your car was injected or carburetted.

The radiator could have minimal fluid flow - clogged tubes. Turn the heater on to it's warmest setting w/high fan speed and see if it stabilizes the temperature.

The water pump could be worn out (impeller not efffective or cavitating)

A blown headgasket has to `blow' something somewhere. One place would be coolant into the oil supply. This is indicated by `milky' or `grey' colored oil on the dipstick as well as the filler cap as you have noted.

The other possibility would be combustion gasses escaping into the coolant. This can be identified by very carefully using a rag or some other method, remove the radiator cap (not the cap on the catch bottle) while the engine is idling. Slowly increase the revs and look for bubbles in the coolant. If you have them, it is either water pump or head gasket. Opening the catch bottle will never produce any sound as the system is not sealed at that point. The sealing is done at the radiator cap which incorporates a pressure relief system to vent into the bottle and siphon back when cooled.

[Sharky]

The car is injected and I changed spark plugs about a year ago but I already had the overheating before that. Likewise, the injectors were cleaned when the sparkplugs were changed. Did an exhaust gas test a couple of months ago and everything seemed to be OK. The radiator was fixed and unclogged a couple of months ago as well.

This is what happens. the car is small engined (1.1L) so you have to force it a bit, particularly when going uphill. About a month ago I was traveling on an uphill road (somewhat steep) with a full passenger load. When I was doing between 65-75 kmph in third gird with high revs and full throttle nothing happened. But as soon as I drove into traffic and had to slow down to 45-50Kmph (second gear, full throttle and high revs again) the overheating light would come on within a couple of minutes. This happened about 3 times during the 1 hour uphill drive. The first time I pulled over and turned off the car. I heard the cooling fan at full speed and it stayed that way for about 5 minutes or so before shutting down or going into low speed. However, the second time it happened I pulled over, turned off the car but as soon as I turned it off I noticed that there was no noise coming from the fan (BTW, my car is one of those in which the fan works independently of the ignition switch). As soon as I got down I heard it starting. That was certainly not normal as the car was supposed to be overheating. The last time it overheated I could hear the fan (or so I reckoned) but it stayed on for quite a while. As a matter of fact, I could touch the radiator, feel that it was cool (cooler than under normal operation) but the fan was still going at full speed.

So my conclusion was: the fan switch is damaged. Instead of going into second speed as it should it's shutting down completely. This made sense as I had no overheating problems when I was doing relatively high speeds, and therefore had more air flow to the radiator than when I was doing slower speeds with the same load. But we ran several tests on the switch with my mechanic and it seemed to be working fine. Which brings me to possible cause #2.

Some months back (before replacing the battery) I had a number of electrical problems. The main problem was that I couldn't turn on the car when "medium/high power" electrical devices (lights and cooling fan in particular) were on. I would turn the key and nothing would happen. The car wouldn't even try to start (as it usually does with a dying battery). I couldn't even hear the starter motor doing anything. Replaced the battery (as the old one was over 5 years old anyway) and the problem apparently stopped. I could turn on the car even if the lights were on just as it should. However, during one of these overheating stops I tried to turn on the car while the fan was running at full speed and I got the problem again. I had to remove the cover from the stereo, turn off the lights and even remove my foot from the brake pedal to avoid turning on the brake lights in order to get it started (as the fan was still going at full speed).

So possible cause #2 could be that there's some kind of electrical problem. Namely, when there is already some kind of load on the electrical system (car running, lights on, etc), a high load condition (fan at full speed or starting the car) cannot be met so, for example, the car won't start or the fan won't go into full speed. Only removing the initial load (turning off the lights, the car, the stereo) would allow for this "high load" demand to be met.

But the strangest thing is that this overheating only happens when I'm on uphill roads at relatively low speeds. It NEVER happens with urban traffic. No matter how hot the day is or how bad the traffic jam is. It is only under constant high load conditions that this happens.

What could it be? I'm really frustrated.

BTW, the cooling fan only has 2 speeds. The highest, which is the one I mentioned, is never used under normal urban traffic. With regular use it just uses the lowest.

BTW, sorry for the long post but I wanted to describe the problem as accurately as possible. Any advise would be greatly appreciated

[thebear]

Definite looks like a `fan control' problem. However, the fan control might be coming from a `black box' (engine control module). The black box can retard the spark, lean out the mixture as well as direct the fan to run at high speed. If you have a bad water temperature sensor feeding the black box all sorts of `wrong' things can happen. I would asume that the fan does not turn on until the normal operating temperature is reached and then it cycles as needed (on-high-on-off). Do you have an actual teperature gage or a light that lights to indicate high tmperature?

[Sharky]

The fan switch isn't connected to any black box. In fact, it is a "bolt" that is screwed to the radiator and has 3 electrical pins (I assume that one is always charged and the other two are for low or high speed). I had to replace it when I bought the car because it would get stuck and drain the battery. The circuit also hay a "relay" which is a small metal cylinder clamped to the top of the radiator.

Unfortunately I don't have a temp gauge on the dashboard and therefore have to rely on the warning lights. Although I'm pretty sure it was overheating because the engine compartment was very hot.

[thebear]

Originally Posted by Sharky

The fan switch isn't connected to any black box. In fact, it is a "bolt" that is screwed to the radiator and has 3 electrical pins (I assume that one is always charged and the other two are for low or high speed). I had to replace it when I bought the car because it would get stuck and drain the battery. The circuit also hay a "relay" which is a small metal cylinder clamped to the top of the radiator.

Unfortunately I don't have a temp gauge on the dashboard and therefore have to rely on the warning lights. Although I'm pretty sure it was overheating because the engine compartment was very hot.

In a prior post you said:

Originally Posted by Sharky

BTW, the cooling fan only has 2 speeds. The highest, which is the one I mentioned, is never used under normal urban traffic. With regular use it just uses the lowest.

The most obvious solution is to force the "high speed" and see if in fact it is working. With the car parked and idling insert a piece of cardboard to cover the radiator (start with ~half, use something you can easilly remove if things get too hot too fast). Try and get a true thermometer (perhaps a probe type, used in cooking) and monitor the actual water temperature (remove the radiator cap) at which the fan operates/changes speed.

I would also question the function of the "The circuit also hay a "relay" which is a small metal cylinder clamped to the top of the radiator." If it is fastened to the to the top of the radiator it may have deteriorated due to heat or it may also have some type of temperature sensor. I think `we' are getting closer.

[Sharky]

OK, I'll try that and I'll get back to you. Thanks

BTW, is there any kind of test I could do on the relay? I have a multimeter if that helps.....

[Sharky]

Mhhh, wait a minute. I think we might have a problem because the fan is located in front of the radiator. In other words, it blows air instead of "sucking" it in. Will it work anyway if I just place the cardboard on the back of the radiator?

[thebear]

Originally Posted by Sharky

OK, I'll try that and I'll get back to you. Thanks

BTW, is there any kind of test I could do on the relay? I have a multimeter if that helps.....

It depends upon how may wires there are and if you can disconnect them easily. Remember that automobile electrical systems run 12v wiring that is always energized from the approprite fuse to whatever device is to be operated. The `switching' action that takes place in what you are calling your fan switch, for instance actually "Grounds" the circuit and completes it. Check voltage from ANY location to ground. There is NO `neutral' or `return' wire as you would find in your home wiring. Your three wire fan switch should have a wire that goes to a ground somewhere and two wires with a constant 12v. That means that it is possible that the wire for `high speed' is NOT energized at all, resulting in no high speed operation. The two wires with 12 volts probably connect to your `relay' somehow but what you are calling a `relay' might actually be the temperature sensor. Can you get a wiring schematic from your car dealer or is there one in in your owner's manual?

[Sharky]

I just went down and took a couple of pictures (now that I have a digital camera ). Sorry for the dirt

This is the fan switch that is plugged into the radiator:

http://pwp.007mundo.com/chsoto/DSCF0538.JPG

And a couple of pictures of the "relay"

http://pwp.007mundo.com/chsoto/DSCF0535.JPG

http://pwp.007mundo.com/chsoto/DSCF0533.JPG

Also, here's a screenshot of a repair manual for this car which refers to this as relay:

http://pwp.007mundo.com/chsoto/manual.jpg

Thanks

[thebear]

The identified components are:

1. Fan, if it has two wires the only way to provide a slow speed is by dropping the voltage from 12 to 6 (?). If it has three wires, they are individualy energized to provide the two speeds via differnt windings in the fan motor. Wire colors are (?)

2. Temperature switch, three wires (green, blue white)

3. Relay, two wires (probably a temperature activated switch as it is on the hottest part of the radiator)

The pictures have changed my `overnight' thoughts.

I believe the `relay; also has an internal resistor (single speed two wire fan only). 12v from the battery goes to a fuse then to the relay, then to the fan, then to ground to complete the circuit. The resistor is in the circuit to drop the voltage to ~6v so you get 'slow' fan speed. When the temperature rises sufficiently, the `relay' will bypass the the resistor and allow the full 12v to run the fan at `high' speed.

The three wire temperature switch MAY prevent the fan from operating until the water temperature at the bottom of the radiator reaches 85-90° C. The bottom of the radiator is the coolest place and that is where the coolant returns to the water pump. Without tracing the wires I can not offer any other help.

I would determine the color of the wires, follow them if possible and search for the fuse that feeds the circuit. Then try and draw a schematic, noting wire colors and connections.

As the fan is not dependent on the ignition switch, using your multimeter with an aligator/crocodile clip on the black lead (-) fastened to a good ground and a common straight pin or safety pin on the red lead probe the appropriate wires to determine when various parts of the circuit are enregized and if there is in fact 6 or 12 volts present. Pushing the pin into the insulation will not cause any significant harm to the wires.

It is also possible that the ignition switch permits initial fan operation but one of the connections to the temperature switch will bypass the ignition switch to maintain power until the temperature drops to a safe level when the key removed from the ignition.

When checking across the terminals of components that are `switches', a "Zero" voltage indicates a `closed' switch, 6 or 12 volts indicated the switch is open. The voltage is truly named "Potential" as it CAN do work.

I wish that I was there `looking over your shoulder' but that is obviously impossible. My `instincts' point to the `resistor' (wherever it is located) as the cause of your other electrical trouble as well.

[COLIN STUBBS]

try a replacement radiator its more than likely blocked in the pipes inernally and no amount of cleaning will make it cool.

[Sharky]

You've been very helpful, even if you're not right here.

I've been doing a couple of test and I think you're right. I unplugged the 3 wire connector that went into the fan switch and tested it with the multimeter. I got 12 volts when testing green-white and green-blue. Therefore green is always energized and white and blue are the ones that ground the circuit. Then I used a piece of wire to short circuit and found that green-blue is low speed and green-white is high speed. Then I unplugged the relay wires and plugged the multimeter instead. When I short circuited green and blue (low speed) I got 12 volts and got no volts when short circuiting green and white (high speed). Also, the blue wire goes into the relay and comes out as the white wire that goes into the fuse box while the white (high) goes directly into the fuse box from where, I would assume, it goes into the fan.

So indeed, as you suggested, the relay is nothing more than a resistance that reduces voltage to the fan when going into low speed.

But then I did this test. I short circuited green-white to get maximum fan speed (which I got). Then I started turning on every electrical device inside the car (Radio, heater, lights, braking lights, warning lights, etc.). As I started turning everything on I could hear the fan reducing its speed. Finally, when everything was on I tried to turn on the car and, as I suspected, nothing happened. Once again I couldn't even hear the starter moving (although everything inside the car was shut down as I turned the key, which is what any car does when it starts). tried again and it finally started.

Which brings me into this little detail. Since I bought the car over 5 years ago (I bought it second hand) I always noticed that the windshield wipers were somewhat "weak". They would always have a little "shake" when operating. Recently I had to replace the alternator's regulator and I noticed that as soon as it was replaced the wipers were opperating very strongly as they never did. But after a while they went back to their usual operation. I don't know if there's perhaps some kind of "power management device" that is failing and isn't sending enough power to certain devices.

[thebear]

Originally Posted by Sharky

You've been very helpful, even if you're not right here. I don't know if there's perhaps some kind of "power management device" that is failing and isn't sending enough power to certain devices.

Yes. The voltage regulator that is usually built into the alternator. However, it may be as simple as a loose alternator belt. It is possible for the belt to slip if it is not tight enough and the electrical load is high enough. This will result in lower voltage available to run things and you know what happens next. Check your service manual for the correct `slack' (~5mm) and see what yours is. It should be checked at the middle of the longest span of the belt.

With the car shut off, measure the voltage at the battery and try to find a connection method that will stay in place. Locate the meter where you can see it from inside the car and secure so that it does nor fall over when the car is started/running. It should be at least 13v and as much as 14.4v. Next, start the car with no accessories running and check again. Slowly increase the engine speed and see if the voltage goes up to ~15-16v. That is a sign of a healthy alternator/regulator. If not, have it evaluated by a specialist auto electric shop or just replace it. I think you have your answer.

[thebear]

¿El tiburón, dónde está usted? ¿Corre el automóvil bueno?

Mister shark, where are you? Is the car running ok?

Any of the `lurkers' out there have any comments on this exchange of messages? There are at least three of you.

[Sharky]

ja ja ja! Thanks thebear. Yeah, the car is running OK as usual. The problem only arises when I take it on an uphill road which is abou6t once a year so I haven't had the chance to test it. I haven't had the chance to check the alternator as I have a very "inaccurate" analog multimeter. Although I know that the belt isn't slipping. As a matter of fact, I changed it a month ago or so.

Anyway, I'll be sure to tell you of any new developments.

Thanks a lot. You've been very helpful and I've learned a lot.

Muchas pero muchas gracias

[Sharky]

new developments. I did the tests with my multimeter. bear in mind that it is not very accurate so what matters is the relative result.

I connected the multimeter to the battery and got 13.5V. As I started the car it went down a bit and the climbed to 14.5 at idle speed. The odd thing was that when I accelerated it the voltage didn't change. The needle didn't even move one bit.No matter how fast the engine ran it kept on showing the same voltage.

then I did the stress test. Short circuited the fan to make it run at full speed, turned on the heater, the lights, the brakes and even the reverse light. The voltage went down to about 12.5-13V. As I turned the ignition nothing happened (as expected the starter motor didn't even start) but what was surprising was that the voltage, once again didn't change either. The accesories (appart from the fan and lights) went off as I turned the key but the voltage remained unchanged. As soon as I turned off the lights, released the brakes and the reverse (but kept the fan running) I started the engine and everything worked as usual.

Isn't that odd? Should the voltage remained unchanged? My multimeter is inaccurate but it is as sensitive as it should be when it comes to voltage changes.

But another thing happened today. My every day commute is through a road that's made on the side of the mountains (but it is paved with traffic lights, 2 lanes and such....like any normal road). That means that it has many uphill and downhill parts (not to mention many corners) although they are very short. No more than 300-500 meters long. that's why it never overheats, unlike long and constant uphill roads. Anyway, today I was going through the steepest part of the road (a 200-250m uphill part which is very steep....30° or a bit more perhaps) but there was a bit of a traffic jam so I climbed in first gear at 15-20kmph. As I was reaching the summit the water level warning light went on. The cooling system has a couple of minor leaks so I thought that perhaps I forgot to check it and it went dry. Although it seemed strange as I had just filled it up last weekend and the leaks are so small that I have to fill it up once every 3-4 weeks. I ended my trip and I didn't got the light during the rest of the trip. But when I went to check the water level it was full!! It hadn't lost a single drop of water. Came back and I didn't get the light again. What could this mean?

Let's see if we can finally crack this one

[thebear]

Originally Posted by Sharky

new developments. I did the tests with my multimeter. bear in mind that it is not very accurate so what matters is the relative result.

I connected the multimeter to the battery and got 13.5V. As I started the car it went down a bit and the climbed to 14.5 at idle speed. The odd thing was that when I accelerated it the voltage didn't change. The needle didn't even move one bit.No matter how fast the engine ran it kept on showing the same voltage.

That is an indication that the voltage regulator is working but I would think that a higher voltage would be present. Check the book for alternator output specs. When you have some time, before you start the engine it might be a good idea to clean up the the `Ground' connections. The negative cable from the battery goes either to the engine block or the car body. Clean/scrape both ends and apply an dielectric/anti-corrosion compound/spray if you can find one. If not, use WD-40. A poor ground can cause all sorts of electrical problems that are unrelated to any diagnostic tests. It will also insure that your battery is properly charged.

Ask your mechanic friend if he has a `hygrometer'. It looks like an `eye-dropper' (glass tube, tapered at one end and a rubber squeeze bulb at the other). Inside are a group of small floating balls or a larger float. They will be color coded and read the specific gravity of your battery's electrolyte. Check each cell. They should be within 0.05 of each other - normal is ~1.28 (I think). The color coded marks (red/yellow/green) to indicate charge/condition. If one cell is significantly lower than the others, it is time for a new battery as the low cell is what is preventing charging to a higher voltage (15/16vdc) and possbly preventing fan from getting the full voltage when it needs it.

Originally Posted by Sharky

I ended my trip and I didn't got the light during the rest of the trip. But when I went to check the water level it was full!! It hadn't lost a single drop of water. Came back and I didn't get the light again. What could this mean?

Possibly a bad temp sensor. Best bet is to run the car while parked and have a real thermometer of some sort on the radiator or near where the temp sensor is located. Block off the radiator or possibly disconnect the fan somehow and see what the indicated actual temp shows when the light comes on. It is possible that the light comes on BEFORE the fan starts. That says the calibration is bad on the fan speed switch OR the sensor.

¡El oso es el jefe! The bear is the boss!

[Sharky]

Originally Posted by thebear

Possibly a bad temp sensor. Best bet is to run the car while parked and have a real thermometer of some sort on the radiator or near where the temp sensor is located. Block off the radiator or possibly disconnect the fan somehow and see what the indicated actual temp shows when the light comes on. It is possible that the light comes on BEFORE the fan starts. That says the calibration is bad on the fan speed switch OR the sensor.

¡El oso es el jefe! The bear is the boss!

However, it wasn't the temperature warning light but the water level warning light.

Also, aren't there any "home-made" rust and corrosion removers? Isn't coke or water and baking soda supposed to work as well?

Great spanish BTW Tal vez podamos seguir discutiendo este asunto con el carro en español

[thebear]

Originally Posted by Sharky

However, it wasn't the temperature warning light but the water level warning light.

Ah-HAH! You didn't say that before. We now have two distinct problems:

1. Water that comes and goes:

Before you start the car in the morning, verify that the overflow catch bottle has fluid at the appropriate level. There should be maximum/minimum indications molded into the plastic. This is your starting point. Check it each morning for two or three days. This allows the coolant to siphon back into the cooling system and gives you a constant reference. Checking it after driving for any period of time will show you how much has been displaced due to normal expansion. The morning check will tell you if in fact you have been losing any coolant. It is then necessary to find where it has been going which could be your original `head gasket' problem OR it could be expanding due to excessive heat and overfill and leak out of the overflow catch bottle. This would show up the next morning as a lower level in the bottle and should be visible wherever the end of the hose from the bottle can be found.

2. Possible causes excesssive heat:

A. Going back to my earler comments, the thermostat may be stuck or possibly not opening completely.

B. A fan that should switch to high speed but doesn't.

C. Low water level due to leakage.

D. Defective radiator cap.

It is possible to pressure test the cooling system. A different radiator cap is installed and a hand pump is used while observing a pressure gage. What is the altitude where the light comes on? The boiling temerature drops significantly over 1km. Are you using any anti-freeze? A 50% mix will help reduce boil off and conduct heat better as well. The system shoud be capable of 1.2-1.4 bar. If there is leak-down during the test, you need to find the location.

A correction to the my previous answer: Use a "HyDrometer", not a "HyGrometer". The 1.28 specific gravity is correct but only at 20°C. If it is REALLY important to you, add 0.004 if over 25°C and subtract the same for 15°C. In other words, forget it.

The observed 14.5v is considered NORMAL. I found some old repair books and those parts of car service haven't changed in 50 years (when the 12v system was adopted).

Originally Posted by Sharky

Also, aren't there any "home-made" rust and corrosion removers? Isn't coke or water and baking soda supposed to work as well?

No. You need something really caustic. Commercial stuff is best.

Originally Posted by Sharky

Great spanish BTW Tal vez podamos seguir discutiendo este asunto con el carro en español

Probably would get both of us in trouble as "English" is the official language of the forum. See the FAQ . In addition, my Spanish is extremely limited. If I need another language, I use THIS WEB SITE . I can get along in French and did so as a Marshal at LeMans in '99->'02.

[Sharky]

I think I know where the missing water is going. There's a small leak in the radiator and there's another one from the heater which leaks a bit right next to the pedals. I assume the latter is probably a "baked" seal in the system. Although I do have to say that there doesn't seem to be coming that much water out of those 2 spots which could indeed mean a faulty gasket. In the morning there aren't any puddles on the floor or anything.

The overflow bottle is hermetically sealed so there aren't any spillovers. In fact, during the last overheating scenario I checked both the bottle and hoses and found no leaks or humidity anywhere. Also, the water level in the bottle was the same as it was when the engine was cold.

I doubt it is the radiator cap as it was changed a couple of months ago for a new one although for a different reason.

Also, I live at 2600 meters above sea level. I once thought that the overheating happened because I was traveling from lower altitudes (and hence, hotter regions) but the last time I got overheating at 2800 meters above sea level and a considerably cool atmospheric temperature.

As for the anti freeze I've used several brands (including havoline Dex Cool if I'm not mistaken) as well as plain water (freezing is not much of a concern here as the temperature in the morning rarely goes below -5°C). No difference there.

I guess a partially open thermostat could explain could explain all the symptoms as it could be open enough to allow enough flow to cool during low/medium load situations but it could actually restrict the extra flow needed during high load conditions.

Although I'm starting to think that my mechanic was right and the gasket is damaged. Oh dear

The thing about this problem is not so much that it hampers my every day commute (as it doesn't) but that it is so frustrating. I rarely take the car out on the road but every time I take it I sweat bullets during the whole trip just waiting for the warning light to go on.

Originally Posted by thebear

No. You need something really caustic. Commercial stuff is best.

Right, coke is supposed to be good at cleaning toilets and unclogging drains. Maybe I'll pour some coke into the radiator the next time the engine starts overheating....who knows!

Originally Posted by thebear

Probably would get both of us in trouble as "English" is the official language of the forum. See the FAQ . In addition, my Spanish is extremely limited. If I need another language, I use THIS WEB SITE. I can get along in French and did so as a Marshal at LeMans in '99->'02

Yeah, I know. I once proposed to the admis to create a "foreign language" forum as I had already seen it in several forums but they didn't like the idea too much. Mainly because they said that they couldn't control what was being said.

I also know a bit of french. Been learning german for over 4 years now and I still haven't got the hang of it.

[thebear]

Originally Posted by Sharky

The overflow bottle is hermetically sealed so there aren't any spillovers. In fact, during the last overheating scenario I checked both the bottle and hoses and found no leaks or humidity anywhere. Also, the water level in the bottle was the same as it was when the engine was cold.

That doesn't sound right. What good is an expansion tank that coolant can not expand into? Maybe that is the cause of your overpressure. The tank should be vented to the atmosphere. Perhaps it has the wrong cap?

Originally Posted by Sharky

Also, I live at 2600 meters above sea level.

That would put the boiling point at ~85°c. Maybe you do have a completely pressurized system. If that is the case, I have no other answers.

Originally Posted by Sharky

I once thought that the overheating happened because I was traveling from lower altitudes (and hence, hotter regions) but the last time I got overheating at 2800 meters above sea level and a considerably cool atmospheric temperature.

But it hasn't overheated, has it? The coolant level was indicated as `low'.

Originally Posted by Sharky

As for the anti freeze I've used several brands (including havoline Dex Cool if I'm not mistaken) as well as plain water (freezing is not much of a concern here as the temperature in the morning rarely goes below -5°C). No difference there.

Except for the heat transfer ability.

Originally Posted by Sharky

I guess a partially open thermostat could explain could explain all the symptoms as it could be open enough to allow enough flow to cool during low/medium load situations but it could actually restrict the extra flow needed during high load conditions.

Although I'm starting to think that my mechanic was right and the gasket is damaged. Oh dear

The thing about this problem is not so much that it hampers my every day commute (as it doesn't) but that it is so frustrating. I rarely take the car out on the road but every time I take it I sweat bullets during the whole trip just waiting for the warning light to go on.

That is what the pressure test will prove.

[Sharky]

I've just looked at a couple more things. I followed the trail of the negative cable from the battery. One goes directly into the fuse box and the other, just as you mentioned , goes into the engine block. Just below the air intake manifold. Very hard to access. I couldn't actually see were the cable is connected but I inspected the visible surroundings and I found this:

http://pwp.007mundo.com/chsoto/DSCF0586.JPG

I noticed a white/blue compound that looked like corrosion that had fallen on the starter motor (lower circle) and also some on the engine block itself (it looks yellow because I had the lantern pointing there).

Since I couldn't actually see what was down there I decided to take my camera and take a couple of pictures of the area from below and I found this:

http://pwp.007mundo.com/chsoto/DSCF0588.JPG

The horror! Now, I still can't quite make out where exactly is the ground wire connected to but, from what I could feel with my hand, it shouldn't be more than an inch away from all that corrosion. From what I can make out I think it is the "red" wire from the picture.

Now, I'm not so sure but I don't believe that this is normal (BTW, I haven't mentioned it but the car is almost 10 years old and has 97.000Km. I live very far from the sea (over 1000 km) and other corrosion sources. The air is rather dry although it does rain often). Could this be indeed the cause of my electrical problems? And if so, will spraying an anti-corrosion compound do the trick or will I have to take these wires apart? (hoping it is not the latter because access is VERY difficult and I would probably need assistance from my mechanic).

As for the catch bottle. Although it is hermetically sealed (the cap is the original one) the "max" mark is located at about 3/5 which still leaves 2/5 (or perhaps a bit more) for expansion.

[thebear]

Originally Posted by Sharky

Now, I'm not so sure but I don't believe that this is normal (BTW, I haven't mentioned it but the car is almost 10 years old and has 97.000Km. I live very far from the sea (over 1000 km) and other corrosion sources. The air is rather dry although it does rain often). Could this be indeed the cause of my electrical problems?

Most definitely. Ambient humidity can speed up corrrosion but it will happen eventually if there is any opening in the surface protection. Given the age and the fact that it is an electrical connection it looks normal (bad).

Originally Posted by Sharky

And if so, will spraying an anti-corrosion compound do the trick or will I have to take these wires apart? (hoping it is not the latter because access is VERY difficult and I would probably need assistance from my mechanic).

Start with a wire brush and remove as much as you can. Then get an old toothbrush and "Baking Soda/Sodium Bicarbonate" and dip the brush in water, then the powder and go after it again until you have a good look at the connection. To be REALLY AND TRULY fixed, you should disssemble and clean everything. The fact that there are several wires in the group means that you have found the one place on the car where all the ground wires terminate. This could make all kinds of things operate better.

[Bluebottle]

Originally Posted by thebear

Probably would get both of us in trouble as "English" is the official language of the forum.

I'll let you off this time