Does engine oil cool slower than water?
Discussion
We all understand the importance of letting your engine oil warm up before (in mungo speak) giving it "johnny large potatoes" 
, and most will know that the oil temperature lags that of the water temperature when warming up (put another way, water temperature is no indication of oil temperature).
Does the opposite happen when the engine is cooling down when turned off after a run i.e. does the oil remain hotter than the water temperature? Not having the luxury of an oil temperature gauge
it is difficult to tell (perhaps our Tuscan owning friends can help out).
I'd like to know so that I have some idea, when starting the car after it has already been warmed, how much quicker the oil gets up to temperature.
, and most will know that the oil temperature lags that of the water temperature when warming up (put another way, water temperature is no indication of oil temperature). Does the opposite happen when the engine is cooling down when turned off after a run i.e. does the oil remain hotter than the water temperature? Not having the luxury of an oil temperature gauge
it is difficult to tell (perhaps our Tuscan owning friends can help out). I'd like to know so that I have some idea, when starting the car after it has already been warmed, how much quicker the oil gets up to temperature.
My 106 has an oil temp gauge and it always amazes me how quickly it cools down after I've switched it off. Can drop below what I would regard as GLF temperature within 20 mins.
Still, it also warms up again very quickly (retained heat in the engine I guess) and I figure that there'll still be some oil clinging to the metal bits. Might be wrong.
Still, it also warms up again very quickly (retained heat in the engine I guess) and I figure that there'll still be some oil clinging to the metal bits. Might be wrong.
The specific heat capacity of water is lower than the specific heat capacity of oil which is why it takes longer to heat up, similarly it takes longer to cool down. To work out the difference in heat-up/cool-down times you would need to know the specfic heat capacity for water and the oil you're using.
The specifc heat capacity is the amount of energy (in Joules) that it takes to raise the temperature of 1kg of a substance by 1 deg C.
The specifc heat capacity is the amount of energy (in Joules) that it takes to raise the temperature of 1kg of a substance by 1 deg C.
alfa dave said: The specific heat capacity of water is lower than the specific heat capacity of oil which is why it takes longer to heat up, similarly it takes longer to cool down. To work out the difference in heat-up/cool-down times you would need to know the specfic heat capacity for water and the oil you're using.
The specifc heat capacity is the amount of energy (in Joules) that it takes to raise the temperature of 1kg of a substance by 1 deg C.
Revising your Boyles law for your 'A' level mocks are you?
or is that the one about pressure being proportional to temperature but inversly proportional to volume...
...hang on, dP(haven't got a delta I don't think)=dT/dV
...or something.
It's the same as that question you always get about the hot cup of tea and the cold milk isn't it.
I'll get my coat.
>> Edited by danger mouse on Friday 17th January 14:14
I would have thought the specific heat capacity of the water would be higher, and hence require more energy to heat/cool.
alfa dave said: The specific heat capacity of water is lower than the specific heat capacity of oil which is why it takes longer to heat up, similarly it takes longer to cool down.
I also think things are a bit more complicated than this. The rate of temperature change depends not only on the heat capacity, but on the rate at which heat energy is lost. The latter is more tricky to calculate.
To work out the difference in heat-up/cool-down times you would need to know the specfic heat capacity for water and the oil you're using.
There are load of factors involved. The water jacket is generally further away from the source of the heat, whereas the oil has to cool the hot moving bits directly. Also depends on the amount of Oil cf amount of water in the system. Generally there's more water. Plus some cars have oil that is cooled by the water (eg 928) or by it's own oil radiator (some Ferraris).
If you're using a modern mutligrade oil, the temperature will have much less of an effect on it's lubricating ability, so I wouldn't worry about it.
Rule of thumb, if warm air is coming out of the air vents it's safe to cane it
If you're using a modern mutligrade oil, the temperature will have much less of an effect on it's lubricating ability, so I wouldn't worry about it.
Rule of thumb, if warm air is coming out of the air vents it's safe to cane it
danhay said:
Rule of thumb, if warm air is coming out of the air vents it's safe to cane it
Unfortunately, not even close. The 106 blows warm within 1/2 mile of home even on cold mornings, but the oil is not warmed until at least 4/5 miles away.
Have no idea on the Chim (no gauge), so just use landmarks where I know the 106's oil is ready for fun.
Have no idea about the theory behind it (economics man, y'see) - just based on observation.
Most (90% +) of your engine wear happens in the first few seconds - coz the oil has drained away to the sump.
You also want the moving bits to warm up so that they expand and fit properly. All this has happened by the time you are getting warm air through the vents, coz the engine has to be warm to warm the water which then warms the air.
If it's any consolation, I've never worn out an engine, even though my 928 has done more miles than Captain Kirk
You also want the moving bits to warm up so that they expand and fit properly. All this has happened by the time you are getting warm air through the vents, coz the engine has to be warm to warm the water which then warms the air.
If it's any consolation, I've never worn out an engine, even though my 928 has done more miles than Captain Kirk
While we're batting controversial theories around, how does this sound?
I usually stick to 2,500rpm religiously until oil is warm. However, I sometimes wonder if this means my engine is not getting enough wear and, therefore, if I should boot it from cold every now and again to loosen it up a bit.
Fascinating hypothesis or load of old arse?
Discuss.
I usually stick to 2,500rpm religiously until oil is warm. However, I sometimes wonder if this means my engine is not getting enough wear and, therefore, if I should boot it from cold every now and again to loosen it up a bit.
Fascinating hypothesis or load of old arse?
Discuss.
cockers said: While we're batting controversial theories around, how does this sound?
I usually stick to 2,500rpm religiously until oil is warm. However, I sometimes wonder if this means my engine is not getting enough wear and, therefore, if I should boot it from cold every now and again to loosen it up a bit.
Fascinating hypothesis or load of old arse?
While Carzee might never lend me one of his cars, I would gladly buy one from you Cockers!
load of arse me old Cock'a. Rich...
cockers said: While we're batting controversial theories around, how does this sound?
I usually stick to 2,500rpm religiously until oil is warm. However, I sometimes wonder if this means my engine is not getting enough wear and, therefore, if I should boot it from cold every now and again to loosen it up a bit.
Fascinating hypothesis or load of old arse?
I think it also depends on where the oil and water go when the engine is turned off (the engine block will be retaining energy). Also if you are in a dry versus wet sumped engine, the oil will be located in a different place. What effect does anti-freeze have (I always thought it improved the cooling effect on the engine) ?
gasblaster said: Mmm, why doesn't someone invent a small oil tank that sits on top of the cylinder head so that oil is dumped into the top of the engine as soon as it turns over?
Not as daft as it sounds, you can buy an oil accumulator that holds oil under pressure when you switch off and dumps it into the engine when you switch on again. So you can have oil pressure before you start the engine.
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