It has been said that running an engine too cool can lead to increased engine wear, specifically the cylinder bores, and I expect the piston rings too?
Is this soley the provision of fuel injected engines or would carburettor engines be equally effected?
I read that the temperature that the top compression ring typically sees is in the order of 160 degrees C. Does that sound correct?
Running a 74 degree thermostat which appears to be the minimum safe temperature,...what difference would the coolant temperature therefore make to the cylinder temperatures, be it a 74, 82 or 88 degree thermostat?
I have also read that an engine should not be driven hard until such time as the engine oil temperature reaches and then exceeds 50 degress C. If this is true, where would be the reference point for measuring this temperature? At the oil pump as the oil enters the engine or in the sump where the temperature would be at its coolest?
All thoughts greatly appreciated.
Ron.
Coolant Temperature and Engine Wear
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Running too cool may increase engine wear and that would be the same no matter what the induction method.
No idea about top ring temperature.
For or the cylinder temperatures I would have to say it would increase to a proportion of the temperature difference based upon the thermal transmittal properties of the construction materials + and scaling or fouling factors.
Its just good practice to let an engine warm up before it gets used hard - for a case in point - the torque required on the oil pump shaft for oil at 5C compared to oil at 50 C.
A great deal of engine lubrication and cooling ( Valve springs, piston crowns) is done by the oil being splashed around and the vapour mist coating all the surfaces this is only really achieved when its hot and less viscous.
For warming up the water temperature gauge is a good indication of oil temperature they follow quite well.
Once the water is up to temperature the oil will continue to heat - the best place to measure oil temperature is the sump as this is the return temperature after its picked up all the heat from the engine and where you monitor to make sure its not over heating - if its too hot in the sump you are in trouble.
Andrew
No idea about top ring temperature.
For or the cylinder temperatures I would have to say it would increase to a proportion of the temperature difference based upon the thermal transmittal properties of the construction materials + and scaling or fouling factors.
Its just good practice to let an engine warm up before it gets used hard - for a case in point - the torque required on the oil pump shaft for oil at 5C compared to oil at 50 C.
A great deal of engine lubrication and cooling ( Valve springs, piston crowns) is done by the oil being splashed around and the vapour mist coating all the surfaces this is only really achieved when its hot and less viscous.
For warming up the water temperature gauge is a good indication of oil temperature they follow quite well.
Once the water is up to temperature the oil will continue to heat - the best place to measure oil temperature is the sump as this is the return temperature after its picked up all the heat from the engine and where you monitor to make sure its not over heating - if its too hot in the sump you are in trouble.
Andrew
4.5L V8 Ginetta G27
I would think carburettor engines are much less affected, however condensation onto the inlet tract surfaces will be marginally higher if the engine is marginally cooler.
And with regard to oil temps, I don't see how a precise figure can be put on it. As I understand it, the reason for not racing an cold engine is because the extra viscosity of the oil causes higher friction in the bearings, causing either bearing failure, or the extra side loading on the little end will shove a rod through the side.
With specific ref to the RV8, the load on the oil pump will be much higher, and may destroy the camshaft or oil pump drive.
This process will be gradual with temp, and oil grade, so I don't race until almost fully warm.
Chris.
And with regard to oil temps, I don't see how a precise figure can be put on it. As I understand it, the reason for not racing an cold engine is because the extra viscosity of the oil causes higher friction in the bearings, causing either bearing failure, or the extra side loading on the little end will shove a rod through the side.
With specific ref to the RV8, the load on the oil pump will be much higher, and may destroy the camshaft or oil pump drive.
This process will be gradual with temp, and oil grade, so I don't race until almost fully warm.
Chris.
--
Series IIA 4.6 V8
R/R P38 4.6 V8
R/R L405 4.4 SDV8
Series IIA 4.6 V8
R/R P38 4.6 V8
R/R L405 4.4 SDV8
Re: Coolant Temperature and Engine Wear
RoverP6B wrote:It has been said that running an engine too cool can lead to increased engine wear, specifically the cylinder bores, and I expect the piston rings too?
Is this soley the provision of fuel injected engines or would carburettor engines be equally effected?
I read that the temperature that the top compression ring typically sees is in the order of 160 degrees C. Does that sound correct?
Running a 74 degree thermostat which appears to be the minimum safe temperature,...what difference would the coolant temperature therefore make to the cylinder temperatures, be it a 74, 82 or 88 degree thermostat?
I have also read that an engine should not be driven hard until such time as the engine oil temperature reaches and then exceeds 50 degress C. If this is true, where would be the reference point for measuring this temperature? At the oil pump as the oil enters the engine or in the sump where the temperature would be at its coolest?
All thoughts greatly appreciated.
Ron.
Hi Ron,
I see that you have a 4.6 lump, I have the same and I run a 74 degree stat. My engine runs between 75-80 degrees, my fan cuts in at about 83.
I have also read that you can get more bore wear if the temperature is kept to low but equally you could class a cracked block and dropped liner as "worn out".....
I believe that the EFI systems are run hotter purely because the EFI system will deliver a rich mixture until the temperature is over 80 degrees because it has been setup to do that. (The engine will eventually end up at 90+ degrees). Rover ran the engines this hot to get an old design through modern emissions tests, they also ran the engine weak which did not help.
I try to run my oil at 90 degrees but as its freezing over here at the moment so it's running around 77 degrees. Personally I measure the oil temperature whilst its in the sump, it must get hotter whilst its splashing around the exhaust valve springs but I think that a good "bulk" reading can be taken from the sump.
Like others have said the engine should not be pushed hard until the oil has warmed up but also the pistons need to heat up to expand to the correct size along with all the other engine components.
All just my humble!
Pete
To Try and explain why wear is increased in a cold engine (and for that matter a hot engine) think of the cylinder liner in isolation of the rest of the block, when it is cold its diamiter drops to a minimum,as you heat it it's diamiter increases (think how you remove a bearing centre that is stuck on a shaft, you heat it up shaft and all) its diamiter goes up at a rate of Pi -1 times the coeficient of expansion of the metal. If it is run cold the clearence on the piston and rings is less than designed and wear goes up.
To see why, when this is the case you also get wear (and potential siezing)when the engine is run too hot there are two factors in play.
Firstly think of the block deck and the bottom bearing area where the sleves of the block pass through as two infitly large plates with holes through them, now as the plates get hotter the holes the liners pass through get smaller with temperature, there is a point where the expansion of the cylinder liner is overcome by the contraction of these holes and the cylinder liners cannot expand any more, secondly there is an ally piston moveing whithin the cylinder liner which can still expand with increasing temperature and as the temp goes up it closes the gap between the cylinder liner and the piston until all siezes solid.
This is why you should not over rev or load a cold engine as at low temperatures the piston is still tight in the bore, further reving/ loading hard causes the piston to heat up repidly having a low mass it expands quickly making things worse.
If you want an extreme example of what I am saying to illustrate what is going on, an F1 engine will not even turn over when cold, the pistons are locked in the bores, to start one they first pump water through then at about 95c and oil at about 120c to get everything to free up enough to be able to fire them up.
There are two reasons for running an engine hotter to get it through an MOT (and why you need heat in a cylinder to get good power from it) firstly a cold engine has a high hydrocarbon level, the combustion reaction is slowed by about 50% for every 10 degrees lower in temperatureat which it ocours so you end up sending out un burnt fuel and oxygen out the exhaust, this makes the exhaust dirty and looses you power. Secondly the the burning of fuel isn't a straight path from hydrocarbon to water and co2 but goes via an intermediate stage of burning to a more hydrogen rich form of hydrocarbon (a simpler single carbon form) and carbon monoxide, this stage releases about 10% of the energy with the oxidisation of carbon monoxide and the hydrogen rich hydrocarbon to water and co2 accounting for 90% of the energy release. this last reaction will only happen if there is enough energy (heat) present, if the combustion temperature is too low it doesn't happen and you throw out alot of carbon monoxide out the exhaust and unburnt hydrocarbons, result even less power.
The ideal situation is to have the top of the combustion chamber (the cylinder head) as cold as you can get it to avoid detonation with a high CR to get heat into the mixture to get combustion going nicely and a thermal barrier between the conbustion reactions and the cylinder head ie. a thermal coating. This by the way is why the coolent flow on the lt and later ls chevy engines is reversed compared to the early SBC so you have cooler heads and a warmer block.
I hope this is of some help.
Best regards
Mike
To see why, when this is the case you also get wear (and potential siezing)when the engine is run too hot there are two factors in play.
Firstly think of the block deck and the bottom bearing area where the sleves of the block pass through as two infitly large plates with holes through them, now as the plates get hotter the holes the liners pass through get smaller with temperature, there is a point where the expansion of the cylinder liner is overcome by the contraction of these holes and the cylinder liners cannot expand any more, secondly there is an ally piston moveing whithin the cylinder liner which can still expand with increasing temperature and as the temp goes up it closes the gap between the cylinder liner and the piston until all siezes solid.
This is why you should not over rev or load a cold engine as at low temperatures the piston is still tight in the bore, further reving/ loading hard causes the piston to heat up repidly having a low mass it expands quickly making things worse.
If you want an extreme example of what I am saying to illustrate what is going on, an F1 engine will not even turn over when cold, the pistons are locked in the bores, to start one they first pump water through then at about 95c and oil at about 120c to get everything to free up enough to be able to fire them up.
There are two reasons for running an engine hotter to get it through an MOT (and why you need heat in a cylinder to get good power from it) firstly a cold engine has a high hydrocarbon level, the combustion reaction is slowed by about 50% for every 10 degrees lower in temperatureat which it ocours so you end up sending out un burnt fuel and oxygen out the exhaust, this makes the exhaust dirty and looses you power. Secondly the the burning of fuel isn't a straight path from hydrocarbon to water and co2 but goes via an intermediate stage of burning to a more hydrogen rich form of hydrocarbon (a simpler single carbon form) and carbon monoxide, this stage releases about 10% of the energy with the oxidisation of carbon monoxide and the hydrogen rich hydrocarbon to water and co2 accounting for 90% of the energy release. this last reaction will only happen if there is enough energy (heat) present, if the combustion temperature is too low it doesn't happen and you throw out alot of carbon monoxide out the exhaust and unburnt hydrocarbons, result even less power.
The ideal situation is to have the top of the combustion chamber (the cylinder head) as cold as you can get it to avoid detonation with a high CR to get heat into the mixture to get combustion going nicely and a thermal barrier between the conbustion reactions and the cylinder head ie. a thermal coating. This by the way is why the coolent flow on the lt and later ls chevy engines is reversed compared to the early SBC so you have cooler heads and a warmer block.
I hope this is of some help.
Best regards
Mike
poppet valves rule!
Many thanks for the replies....much appreciated... 
I guess my question on driving an engine hard was more to do with the oil temperature exceeding 50 degrees C, and if that was indeed considered an acceptable temperature.
I have an oil temperature transmitter mounted in the sump plug, so typically anywhere from 60 to 90 degrees would be normal depending on the ambient temperature and the driving conditions, be they city or open road. The hottest I have seen was 125 degrees C, and that was on a 35 degree day in rather heavy traffic. Coolant temperature was easily 100 degrees C or more and the temp in the car was 47 degrees....ouch!
That was on my now replaced 3.5.
I have a 13 row engine oil cooler fitted to my 4.6, so oil temps usually range from 60 to 90 with an occassional max of 100 degrees C but no more, even on 38 degree days in traffic with coolant temp past 100 degrees C. I always try and avoid having to drive in such conditions if I can avoid it....just too damn hot!
All this and a 74 degree stat too. In winter the stat proves to be too cool in nearly all driving conditions, so I block off part of the grill with vinyl,...works a treat in keeping the temp just that little bit warmer.
Ron.
I guess my question on driving an engine hard was more to do with the oil temperature exceeding 50 degrees C, and if that was indeed considered an acceptable temperature.
I have an oil temperature transmitter mounted in the sump plug, so typically anywhere from 60 to 90 degrees would be normal depending on the ambient temperature and the driving conditions, be they city or open road. The hottest I have seen was 125 degrees C, and that was on a 35 degree day in rather heavy traffic. Coolant temperature was easily 100 degrees C or more and the temp in the car was 47 degrees....ouch!
That was on my now replaced 3.5.
I have a 13 row engine oil cooler fitted to my 4.6, so oil temps usually range from 60 to 90 with an occassional max of 100 degrees C but no more, even on 38 degree days in traffic with coolant temp past 100 degrees C. I always try and avoid having to drive in such conditions if I can avoid it....just too damn hot!
All this and a 74 degree stat too. In winter the stat proves to be too cool in nearly all driving conditions, so I block off part of the grill with vinyl,...works a treat in keeping the temp just that little bit warmer.
Ron.
4.6 Rover 3500 P6B
kiwicar wrote:To Try and explain why wear is increased in a cold engine (and for that matter a hot engine) think of the cylinder liner in isolation of the rest of the block, when it is cold its diamiter drops to a minimum,as you heat it it's diamiter increases (think how you remove a bearing centre that is stuck on a shaft, you heat it up shaft and all) its diamiter goes up at a rate of Pi -1 times the coeficient of expansion of the metal. If it is run cold the clearence on the piston and rings is less than designed and wear goes up.
To see why, when this is the case you also get wear (and potential siezing)when the engine is run too hot there are two factors in play.
Firstly think of the block deck and the bottom bearing area where the sleves of the block pass through as two infitly large plates with holes through them, now as the plates get hotter the holes the liners pass through get smaller with temperature, there is a point where the expansion of the cylinder liner is overcome by the contraction of these holes and the cylinder liners cannot expand any more, secondly there is an ally piston moveing whithin the cylinder liner which can still expand with increasing temperature and as the temp goes up it closes the gap between the cylinder liner and the piston until all siezes solid.
This is why you should not over rev or load a cold engine as at low temperatures the piston is still tight in the bore, further reving/ loading hard causes the piston to heat up repidly having a low mass it expands quickly making things worse.
If you want an extreme example of what I am saying to illustrate what is going on, an F1 engine will not even turn over when cold, the pistons are locked in the bores, to start one they first pump water through then at about 95c and oil at about 120c to get everything to free up enough to be able to fire them up.
There are two reasons for running an engine hotter to get it through an MOT (and why you need heat in a cylinder to get good power from it) firstly a cold engine has a high hydrocarbon level, the combustion reaction is slowed by about 50% for every 10 degrees lower in temperatureat which it ocours so you end up sending out un burnt fuel and oxygen out the exhaust, this makes the exhaust dirty and looses you power. Secondly the the burning of fuel isn't a straight path from hydrocarbon to water and co2 but goes via an intermediate stage of burning to a more hydrogen rich form of hydrocarbon (a simpler single carbon form) and carbon monoxide, this stage releases about 10% of the energy with the oxidisation of carbon monoxide and the hydrogen rich hydrocarbon to water and co2 accounting for 90% of the energy release. this last reaction will only happen if there is enough energy (heat) present, if the combustion temperature is too low it doesn't happen and you throw out alot of carbon monoxide out the exhaust and unburnt hydrocarbons, result even less power.
The ideal situation is to have the top of the combustion chamber (the cylinder head) as cold as you can get it to avoid detonation with a high CR to get heat into the mixture to get combustion going nicely and a thermal barrier between the conbustion reactions and the cylinder head ie. a thermal coating. This by the way is why the coolent flow on the lt and later ls chevy engines is reversed compared to the early SBC so you have cooler heads and a warmer block.
I hope this is of some help.
Best regards
Mike
Hi Mike.
I'm a little confused by some of the above especially the bit about pistons being tight in the bore when cold. My forged pistons have 2.5 thou clearance when cold and can be heard slapping until they warm up.
The slapping noise does remind me not to drive it hard till warm.
Regards Denis
1950 A40 Devon Hotrod with 5.0 twin turbo RV8.
EDIS8 wasted spark, Holley Injection.
Been as far as the Moon and back in 57 years of driving. Same Car, 5 engine upgrades !!!
EDIS8 wasted spark, Holley Injection.
Been as far as the Moon and back in 57 years of driving. Same Car, 5 engine upgrades !!!
The above is a general case to illustrate that there are several things going on at once, but even in your specific case of forged pistons what I have said holds true.
If you look at the model described you will see that it is very unlikly that the cylinder will remain parrelel as it heats up, it is pinched at either end. In the specific case of forged pistons they have a very high coefficient of expansion, piston slap is generally heard as the piston rocks as the con rod goes from one side of the piston/crank centre line to the other, when things are cold on your engine there is excessive clearance at BDC the piston rocks from side to side and you get the slap, further it is likley the machine shop, if they knew you were fitting forged pistons will have given extra clearance in the bore around BDC to compensate for the uneven expansion of the cylinder. in the case of your engine I would not run it cold as you will get excessive blow by.
What I am trying to illustrate is that part of an engines specification is it's operating temperature, this is established after alot of research by automotive manufactrures, if you change one aspect of that specification without understanding the whole situation and compensating for it you will most likley have adverse effects on the engine as a whole.
Best regards
Mike
If you look at the model described you will see that it is very unlikly that the cylinder will remain parrelel as it heats up, it is pinched at either end. In the specific case of forged pistons they have a very high coefficient of expansion, piston slap is generally heard as the piston rocks as the con rod goes from one side of the piston/crank centre line to the other, when things are cold on your engine there is excessive clearance at BDC the piston rocks from side to side and you get the slap, further it is likley the machine shop, if they knew you were fitting forged pistons will have given extra clearance in the bore around BDC to compensate for the uneven expansion of the cylinder. in the case of your engine I would not run it cold as you will get excessive blow by.
What I am trying to illustrate is that part of an engines specification is it's operating temperature, this is established after alot of research by automotive manufactrures, if you change one aspect of that specification without understanding the whole situation and compensating for it you will most likley have adverse effects on the engine as a whole.
Best regards
Mike
poppet valves rule!
kiwicar wrote:The above is a general case to illustrate that there are several things going on at once, but even in your specific case of forged pistons what I have said holds true.
If you look at the model described you will see that it is very unlikly that the cylinder will remain parrelel as it heats up, it is pinched at either end. In the specific case of forged pistons they have a very high coefficient of expansion, piston slap is generally heard as the piston rocks as the con rod goes from one side of the piston/crank centre line to the other, when things are cold on your engine there is excessive clearance at BDC the piston rocks from side to side and you get the slap, further it is likley the machine shop, if they knew you were fitting forged pistons will have given extra clearance in the bore around BDC to compensate for the uneven expansion of the cylinder. in the case of your engine I would not run it cold as you will get excessive blow by.
What I am trying to illustrate is that part of an engines specification is it's operating temperature, this is established after alot of research by automotive manufactrures, if you change one aspect of that specification without understanding the whole situation and compensating for it you will most likley have adverse effects on the engine as a whole.
Best regards
Mike
Mike, thanks for the reply.
My initial response was made as your comments lead me to think that it's likely that the pistons could seize if the engine was worked hard from cold. Maybe on a F1 engine this may be likely but on a production engine clearances should allow for this with increased ring land clearance. I understand that during the warm up mode if worked hard the top of the piston will expand quicker than the neighbouring materials and temporarily reduces the designed running clearance. However, the rich cold mixture tends to keep temperatures low albeit that it's washing the oil away and causing increased wear.
On a RV8 if seizure is likely when revving from cold I would be worried every time I went through the camshaft initial running-in procedure.
Reference your comments on my particular pistons, these were designed by me and manufactured in the US to my spec. They do as expected slap when cold but have now seen 15000 miles and with no abnornal oil comsumption or blow by.
There must by many guys out there in road cars running loose fitting forged pistons who would not consider pre warming the engine before a cold start. I'm sure they are happy to put up with a bit of slap and wear.
Regards Denis
1950 A40 Devon Hotrod with 5.0 twin turbo RV8.
EDIS8 wasted spark, Holley Injection.
Been as far as the Moon and back in 57 years of driving. Same Car, 5 engine upgrades !!!
EDIS8 wasted spark, Holley Injection.
Been as far as the Moon and back in 57 years of driving. Same Car, 5 engine upgrades !!!
