Overheating Bike Engined Car

[av8rirl]

Hi Folks

I have a problem with a bike engined car. We are running an RF900 tuned to about 120bhp. Engine temp is running at about 96C after about 3 laps... others are running just as high and there have been many terminal failures. I have a few questions which hopefully people with greater knowledge can answer:

1. What engine temp is ideal for the RF900?
2. What is the max engine temp we should run?
3. Where exactly are you taking the temp from?
4. The coolant is literally boiling in the container after 4 laps. Is there any particular coolant recommended?
5. The coolant container sits behind the engine and at a height just below the head. Someone has suggested that moving the coolant container to a position higher than the head will solve the overheating problems. Can anyone tell me if this is accurate? or does it matter where the coolant container is?

Hopefully someone can help out with these questions. All replies are greatly appreciated. Many Thanks. av8r

[1200Datto27]

I cant answer all of your questions, but I'll have a go at some.

Engine temp should be taken (IMHO) at the water outlet from the engine to the radiator, but before the thermostat. This will give the most accurate temp reading for the engine.

The coolant container should be mounted in a position that places it above the highest point in the engines coolant system, this will help to remove any air from the system and reduce hotspots.

Have you tried using a water wetter instead of coolant? I know in my car engines that I have raced it's taken around 10 degrees C out of the system, compared to standard coolants.

[Al Weyman]

I had a marginal rad on my IROC race car and a new alloy one on order (fitted now) but had to do a race before the new one arrived. I stuck in water wetter and can report much to my surprised it really did work. Before after a race it would boil and chuck all the water out even after doing a slowing down lap, post water wetter no problem.

[TwoWheelTerror]

When I owned a tuned R6 it wasn't uncommon to see water temps much higher than 96 C . And it was fine

[knighty]

I design engines for a living and have previously built and raced a BlackBird bike engined single seater so I can answer your questions for you

1) 90-100DegC water temp is fine for track and road use
2) 110DegC is a maximum
3) your temperature gauge should be placed on the block outlet which feeds the rad top hose
4) use redline "water wetter" from deemon tweeks, this reduces the surface tension of the coolant and reduces the temperature by about 5 to 10 DegC
5) Your header tank is most deffo too low - it should be above the cylinder head and above the radiator - move it NOW

some other points of note - the header tank should be on the inlet to the water pump in order to promote a good supply to the pump inlet, and therefore good coolant flow, this is the bottom radiator hose.......otherwise the water pump will cavitate and you will have minimal flow - bad news

Make sure you ARE running the thermostat - never run without it - ignore people who tell you not to

make sure your radiator has some form of duct to ensure the air actually gets forced through the radiator core - otherwise the air will take the easiest route and not pass through the rad-core.....something like a simple 2" high rectangular rim, made from ali sheet, cable tied in place will be fine - place foam between the rad and rim to promote a good air seal and stop the ali peircing the rad.....

are you running an oil cooler???? - max sump oil temp is 140DegC.......ideal is around 100-110DegC.......measure oil temp in the sump only, and nowhere else, again make sure the cooler ducted properly

[norman-normal]

Very good post Knighty, it's nice to have someone with credentials agree with some of the information I've posted. Perhaps now, Old Grumps will gain a degree of respect.

[knighty]

I also forgot to mention - run a 21-25psi cap on your header tank - your standard cap will probably only be around 14-16psi - the extra pressure given from a 21-25psi cap will give you extra safety margin against the engine boiling over on hot track days - its a cheap item that will save your engine from catastrophic failure.

make sure your plumbing can handle the extra pressure - use good quality hose clips - ideally where you use long runs of hose replace it with hard metal tubing - 22mm copper plumbing pipe is quite OK and will not restrict flow - solder on 22mm compression-olives in order to craete a bead for the rubber/silicon hose to seal up against.

[Al Weyman]

20psi cap, yes I put one of those on with the new Alley rad and the thing never went over 180 degrees even after 16 hard laps on a red hot day at Rockingham so yes thats another good and cheap suggestion.

[GordonG]

Not familiar with that particular engine, but Blades and zx12s have an oil to water cooler that runs in parallel with the radiator - so part fo the flow from the pump goes through the rad to cool down, the other part goes thru the oil cooler to heat up (and cool the oil). Get the balance wrong (like by fitting a big rad that has more resistance than the bike rad) and you get more flow thru the oil cooler, less thru the rad and the thing boils up in no time.

Ditch the oil/water cooler if you have one and run oil/air instead.

Everything Knighty says is A1. My zx12r runs 100-107 on track - higher than I would like but it does this all day. Last year I had the "flying kettle" which blew all its coolant out after 3 laps - that was a duff head gasket and half a season of chasing extra cooling was concluded by swapping the engine. If your coolant is "boiling in the header tank" when the coolant temp isnt much over 100 deg then you either have a blown head gasket or (if it's boiling a littel over 100) no pressure in the system.

With a 20psi cap ISTR it shouldnt boil at all till 120 deg plus (not to be recommended!

All temps measured on the exit from the engine/rad top hose.
G

[ian_w]

I also design race engines for a living and whilst I agree with most things Knighty has said, there is no reason why you can't remove the thermostat - in fact none of the engines I work on have stats.

Removing the stat will remove a significant restriction in the cooling system and give a good increase in the water flow rate of the engine, this in turn with improve the cooling of the engine. One downside is that the pressures in the top hose will increase and you will need to make sure the hose and rad are in good condition.

Many stats on modern engines are of a double ended design, as one side opens to allow water to the rad the other side closes that stops water just be recirculated around the engine - with these type of stats you need to be very careful how you plumb it in or you can end up with a situation where no water flows thro the rad.

If you remove the stat then you will have to regulate the coolant temp by taping up the radiator inlet duct. This is only really appropriate for a race or track car if you also use the car on the road then its probably best to keep the stat.

On the header tank location, it should be the highest point in the cooling system. The bottom of the tank should return to the water pump inlet using a hose with an internal diameter of something like 12-16mm. The feed to the header tank should be on the water outlet pipe from the engine, it is very important that this hose is a small diameter, I would say no more than 3mm. If your hose is bigger than this then you need to fit a restrictor somewhere in the pipe. If not, you are creating a large leak path that simply short circuits coolant around the header tank rather than thro the radiator.

[Al Weyman]

Removing the stat will remove a significant restriction in the cooling system and give a good increase in the water flow rate of the engine,

Which could infact then flow too fast through the rad not allowing the air flow time to cool the water properly.

[av8rirl]

Gents... cheers for this info. I now have a plan that looks something like this.

1. Replumb all water pipes with proper tubing.
2. Raise the water coolant reservoir above cylinder head height.
3. 21 - 25 psi cap.
4. Water wetter.
5. Look into possibility of an oil cooler.

And I'll post here to let you know how it goes!!

What temp should I be looking at as an optimum temp? I know from bikes that sometimes some of the rad is covered to restrict airflow if the day is particularly cold. This would indicate that there is a preferred running temp.

Again. Many Thanks.

[MikeBz]

Originally Posted by Al Weyman

Which could infact then flow too fast through the rad not allowing the air flow time to cool the water properly.

I believe that's a myth. Heat transfer is proportional to the temperature gradient. The faster the flow the greater the temperature gradient between the coolant and the airflow, hence the greater the cooling capacity of the system.

[I wonder if I should get in my bunker now...]

Mike

[Al Weyman]

I should have added the theory (as I have read it) is that too fast a flow also does not give the cool water enough time to transfer the heat away from the cylinder block and also promotes cavitation.

[norman-normal]

Not having a thermos cost me a DNF and an engine rebuild, additionally, you do need control of the engine temp; you can run too cool and while it is not as bad as running too hot, it is harmful.
On many computerized cars, running too cold a thermos or none, will make the fuel injection run way rich.

Mr Ian-W you say you design race engines, am I to assume design engines in there entirety or redesign existing engines, for racing?

[Notso Swift]

I see your problem
Your engine id designed for a M-O-T-O-R-B-I-K-E and you drive a C-A-R!
Only kidding, I have been hanging to say that to someone, though.

Ian_w. I think the people who are advocating the use of a thermostat may be confusing is function as a restrictor, vs temperature regulation.
Could you confirm that while you do not use a thermostat, you still use a restrictor?
If so there would not necessarily be an increase on the stress on the top hose, unless the restrictor was after the hose. Otherwise is it a sealed system, where any increase in Temprature results in an increase in pressure?

For information of others – the pressure in the system at the radiator may be at a nominal figure of 15psi, however, in the block it is significantly higher as the water pump is trying to force more coolant through the system than can get back out again. That creates more pressure in the block, as has already been discussed, pressure helps prevent boiling. This is required as the coolant in the really hot parts of the motor, particularly the water jackets near the combustion chambers, will get to 140-160 deg C, and the increased pressure is required to prevent localised boiling. It can be a tight rope that you walk when you have to balance the coolant flow speed, the pressure in the block (as lower speed will invariably mean greater pressure it the rest of the installation is constant), versus the rate it absorbs heat in the motor, versus the rate it rejects heat from the radiator. I will be honest it is a bit hard for a club racer like me, and I use a thermostat as a result! This means the cooling system is not optimised, i.e. it is too big for normal operation, but at least it is safe during extreme conditions.

[knighty]

Ian W - sorry bud - Rubbish - increasing the flow rate of the coolant by removing the stat is a BAD thing to do......if coolant flow is too fast it doesnt hang around in the radiatior long enough - and the engine overheats......fast flow is bad news........as a rule of thumb you need 1/3rd the engine power in L/min as an ideal coolant flow.......so for a 120bhp motor thats 40L/min.....this is well a proven method

Not so swift - This is the exact reason I was saying to use a thermostat - you need about 60-80psi pressure inside the block cooling jacket in order to resist the plate boiling effect created by the heat transfer of combustion.........if anyone is honestly telling me they think they should run 60-80psi in the rest of the cooling circuit - like in the rad and header tank on a hot summers race day race - by removing the thermostat - then sorry, but this is too high risk - even for semi-professional motorsport.

I have designed and converted engines for front running BTCC teams, WRC cars, Super 1600 rally cars and not to mention a few LeMans projects - and I currently design and develop what could be termed highly strung mid-range turbo-diesel engines, and we always run a thermostat......we have never run an engine without.....its too risky.....you are a brave man if you are telling your customer to run the entire cooling circuit at 60-80Psi........perhaps in F3 or F1, but deffo not on a clubbie or semi-pro job

The only engine I have worked on without a stat was an IRL V8 driven by a certain Mr T.Scheckter & co......needless to say they were expensive high-tech motors for US oval racing

yes the majority of bike engines run whats termed a bypass thermostat, if you remove this and dont re-plumb the system accordingly - engine failure awaits you in the not too distant future........bottom line - KEEP THE STAT

Originally Posted by Notso Swift

I see your problem
Your engine id designed for a M-O-T-O-R-B-I-K-E and you drive a C-A-R!
Only kidding, I have been hanging to say that to someone, though.

Ian_w. I think the people who are advocating the use of a thermostat may be confusing is function as a restrictor, vs temperature regulation.
Could you confirm that while you do not use a thermostat, you still use a restrictor?
If so there would not necessarily be an increase on the stress on the top hose, unless the restrictor was after the hose. Otherwise is it a sealed system, where any increase in Temprature results in an increase in pressure?

For information of others – the pressure in the system at the radiator may be at a nominal figure of 15psi, however, in the block it is significantly higher as the water pump is trying to force more coolant through the system than can get back out again. That creates more pressure in the block, as has already been discussed, pressure helps prevent boiling. This is required as the coolant in the really hot parts of the motor, particularly the water jackets near the combustion chambers, will get to 140-160 deg C, and the increased pressure is required to prevent localised boiling. It can be a tight rope that you walk when you have to balance the coolant flow speed, the pressure in the block (as lower speed will invariably mean greater pressure it the rest of the installation is constant), versus the rate it absorbs heat in the motor, versus the rate it rejects heat from the radiator. I will be honest it is a bit hard for a club racer like me, and I use a thermostat as a result! This means the cooling system is not optimised, i.e. it is too big for normal operation, but at least it is safe during extreme conditions.

[Locost47]

Originally Posted by knighty

Ian W - sorry bud - Rubbish - increasing the flow rate of the coolant by removing the stat is a BAD thing to do......if coolant flow is too fast it doesnt hang around in the radiatior long enough - and the engine overheats......fast flow is bad news........as a rule of thumb you need 1/3rd the engine power in L/min as an ideal coolant flow.......so for a 120bhp motor thats 40L/min.....this is well a proven method

I'm certainly going to bow to your much greater knowledge and experience od engines but i do disagree with the "fast flow is bad" point. At work we test cooling systems for a wide range of road & race people including F1 and what we see is that higher flow rates give better overall heat rejection. The temperature drop from top to bottom hose is smaller, sure, and the amount of heat energy rejected per litre/sec of flow rate does drop but not very rapidly and so the overall amount of heat rejected is still greater.

Current F1 radiators run at around 250-350 l/min but they're still trying to go higher and higher. Unfortunately our test rigs top out at 300 l/min so we've actually had to turn them away.

I can't disagree that the thermostat fix does work, but i can only guess that it may be more to do with the effect of the increased back-pressure on reducing cavitation at the water pump, rather than reducing the flow rate.

[MikeBz]

Originally Posted by Locost47

... what we see is that higher flow rates give better overall heat rejection. The temperature drop from top to bottom hose is smaller, sure, and the amount of heat energy rejected per litre/sec of flow rate does drop but not very rapidly and so the overall amount of heat rejected is still greater.

That's what I was trying to say... If half the rad is cold (oversimplifying and taking it to the extreme) then only half the rad is doing anything. If all of the rad is at the input hose temperature then all if the rad will dumping as much heat into the airflow as possible. The rate at which heat is dumped is proportional to the temperature differential between the rad and the airflow, it cannot be affected by the flow rate (other than that the flow rate affects the temperature gradient) - the interface between the metal and the airflow knows nothing of the rate of flow of the coolant underneath it, it only knows of the temperature of the coolant underneath it and the hotter that is the more heat will be transferred.

I confess I'm looking at this from a simple O-level physics perspective and that in the real world there other factors, hence I'm in no position to argue with Knighty's experience that there is an 'optimum' flow rate for a given set of parameters - but there must be reasons which are better and more scientific than the theory that there isn't "time" for heat to be conducted away.

Mike

[GordonG]

OK, I can resist no longer. how much pressure differential can an auto water pump create? If the pressure in the head is higher than the pressure downstream of the stat, this implies that the pump must be holding that pressure up by forcing the water into the head. Given that the pump is a centrifugal pump (not a positive displacement cylinder pump etc) and there is a constant flow, any pressure difference must be due to the "head" that the pump can support - otherwise the water would just flow backwards round the circuit to the downstream side of the stat.

AFAIK, a typical water pump is high flow low pressure - no more than a few feet of water, so the idea that there is hundreds of PSI greater in the head than the rad is, I'm afraid, wrong.

I did a lot of basic physics research on this last year, looking into colling probs of my own, and could find no supporting evidence to the benefits of a flow reduction except
a) if too high a flow results in laminar flow through the waterways of the engine and/or rad, which would reduce heat transfer vs turbulent flow or
b) the stat itself contributes to turbulence or tumble (which given the run of pipes involved I cant see myself).

So, Reynolds numbers and laminar flow. Other than that, more flow is better.

G

[Locost47]

Increasing the flow rate won't make it more laminar, quite the contrary in fact. Higher Reynolds numbers will mean more turbulent but also thinner boundary layers, which is where the heat transfer takes place and both changes are beneficial.

[knighty]

AFAIK, a typical water pump is high flow low pressure - no more than a few feet of water, so the idea that there is hundreds of PSI greater in the head than the rad is, I'm afraid, wrong.

who said 100's more???.....not me.....typical rad pressure is about 14-16psi.........block pressure is around 60 to 80 psi......thats a difference of about 40 to 60psi......not hunderds......its a fundamental requirement of the cooling circuit to have greater pressure in the block & head - otherwise the thing will boil over in no time......its all in order to resist the plate boiling effect.

I find it quite believable that F1 run those sort of flow rates - it follows the theory of 1/3rd engine power in L/min......I hear around 800bhp for the latest 2.4 V8's - so thats around 266 L/min ball park.......nothing new there......I was told by a bloke from Shell F1 that they run the Ferrari F1 coolant temps well into 130DegC, all in order for small rads and reduced frontal area and aero efficiency......needless to say I bet they run monstor coolant pressures and weird coolant mixes........the requirement for fast flow becomes even more believable

I think this is going a little off topic now - matey had an over heating bike engined car, I have said my bit, now we are talking about F1 radiators, reynolds numbers, and which way to go with pump flow rate.......I think we all need to get out more

[GordonG]

Sorry knighty, couldnt be bothered to look back on the thread to see what figures were being quoted. I still doubt a car water pump can push out 40psi - that's quite a bit - more than mains pressure I believe (which is miniumum 1.5 bar or about 22psi from a quick google) even static, let alone through an open stat?

G

[ian_w]

They are bespoke race engines used in various International race series. My job is actually engine development, i.e. running engines on dynos and generally trying to get more power out of them. I do a small amount of actual design work, I just said I was a 'designer' as it is easier for people to understand what I do.

Al - You are definately wide of the mark, more flow equals better cooling, its basic physics. Taking your argument to the extreme, have you considered restricting your coolant flow to get better cooling?!

[norman-normal]

sounds interesting, thank you Ian.