Oil check hot

currymunster · Apr 23, 2018

Really stupid basic question that's been bugging me for ages. I swear I read somewhere that 300tdi oil should be checked hot. I've owned lots of different cars and never come across it before. Why? Please put me out of my misery. Does oil expand when hot and if so why gauge it hot and not cold?
Cheers everyone

Flossie · Apr 24, 2018

Engine has to have been stopped for a while(5mins or so) vehicle level. Doesn't matter if oil is hot or cold in the real world.
The 'wait' is so all the oil that is pumped around the engine has time to run back ,via gravity, to the sump which is where the dipstick sits.
Before a cold start is easiest cos you don't have to 'wait'.

currymunster · Apr 24, 2018

I understand the 5 Minute wait for oil to drop back down to sump. It's just that in the 300tdi owner book it says to check it hot and if it had to be done cold then it needs to be rechecked next time it's hot. Why - What's the difference between hot and cold?

Blackburn · Apr 24, 2018

Oil expands with heat maybe there is a risk of overfilling!

DanClarke · Apr 24, 2018

You sure you are not thinking about Auto gearboxes?
I thought they had to be "level-checked" while hot/warm after having gone through all gears and returned to neutral.

currymunster · Apr 24, 2018

defo for the engine, here is the owner maintenance blurb for checking oil on Discovery 300tdi plus the MPI and V8.

Kwakerman · Apr 25, 2018

It shouldn't really make any difference whether an engine is hot or cold when the oil level is checked. What you are looking for is a consistent and repeatable process, therefore, if the manufacturer states to check it when hot then the dipstick level markings will be set for a hot engine, likewise the opposite is true of a cold engine. Where differences occur is if the manufacturer specifies hot and the owner does cold or. vice versa as that can lead to incorrect levels although whether this would actually be sufficiently incorrect to cause an issue is another question.

Larry328 · Jul 11, 2018

Kwakerman said:
It shouldn't really make any difference whether an engine is hot or cold when the oil level is checked. What you are looking for is a consistent and repeatable process, therefore, if the manufacturer states to check it when hot then the dipstick level markings will be set for a hot engine, likewise the opposite is true of a cold engine. Where differences occur is if the manufacturer specifies hot and the owner does cold or. vice versa as that can lead to incorrect levels although whether this would actually be sufficiently incorrect to cause an issue is another question.[/QUOTE
Completely agree. The level can be much further up the dip stick if you check it after standing for quite a while.

Oil check hot

currymunster

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Flossie

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currymunster

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Blackburn

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DanClarke

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currymunster

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Kwakerman

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Larry328

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