Engine Temperature vs Engine Oil Temperature ?

Engine Temperature vs Engine Oil Temperature ?

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cornflakes2

Original Poster:

230 posts

76 months

Friday 26th February 2021
quotequote all
Is Engine temperature and Engine Oil Temperature different? I think my mechanic said even though my engine oil is at the optimal 90 degrees celsius my engine is running hot. Does this make sense? How? I don't understand it.

If they are different then what is the point of having engine oil temp gauge without having an engine temperature gauge?
I always thought as long as you see the needle at 90 celsius, it means your engine is running at its optimal temperature but it sounds like he was saying my engine is running hot.

andrewcliffe

936 posts

223 months

Friday 26th February 2021
quotequote all
Few cars have an oil temperature gauge.
Many cars have a water temperature gauge.
They are measuring different things.

So if your oil temperature is fine, but your engine is still running hot, it may be that the water system isn't running as efficiently as it could.

Or there is a fuelling issue which is causing the engine to run hot.


cuprabob

14,419 posts

213 months

Friday 26th February 2021
quotequote all
One thing to note that coolant temp gauges on modern cars tend to display 90 over a range, normally between 75 and 105. Oil temp gauges, if fitted, tend to display real time measurements.

Edited by cuprabob on Friday 26th February 10:07

anonymous-user

53 months

Friday 26th February 2021
quotequote all
you WANT engine oil temp to go (well) over 100 degC on most trips if possible!

This is because the combustion process both creates water vapour (though the act of burning) and releases water vapour from the air its ingesting (through the act of compression). And that water vapour finds it's way down past the piston rings and into the block via the normal process of blow-by (piston rings are not 100% perfectly sealed, they leak a little bit).
Once in your block, that water vapour gets captured by the oil and oil mist that is flying around insides as your engine spins and runs.

If you oil temp never exceeds 100 degC, the water content in your oil therefore increases slowly, but continuously, on ever trip, because it never gets hot enough to boil back to steam! This oil "emulsification" is bad for your engine if left for long periods:




At high water-in-oil concentrations, the lubricating properties of the oil are reduced and hence engine wear of moving parts (bearings, rings, cams etc) can suddenly become catastrophic.


So, what manufacturers try to do it to ensure that the engine and its cooling system is designed to operate where possible with the oil well above 100 degC, and modern engines also run with high water temps (for emissions and efficiency reasons).

For a modern car, i'd consider the following temperature ranges to be consistent with "normal" operation


Engine coolant: 90 to 110 degC
Engine oil: 95 to 140 degC


Obviously on short trips, there is simply not time or energy for the oil to warm up, despite manufacturers near universal use of coolant to oil heat exchanges that COOL the oil when it is above the coolant temperature (ie at high loads / speed) but also HEAT the oil when it is below the coolant temp (ie low loads / speeds)


So in short, yes, there is a large difference between coolant and oil temps and no, they are very much not the same things, and no, unless you are regularly seeing oil temps above about 140 degC then there is no worry!



Edited by anonymous-user on Friday 26th February 13:02

E-bmw

9,105 posts

151 months

Friday 26th February 2021
quotequote all
^^^ Wot 'e said.

I was just reading down & was going to post similarly, well done. Couldn't have put it better myself.

ETA. OP, you need to go back & ask him again, as that is not right, your coolant is at 90 (ish) not your oil.