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I was talking to an engineering pal of mine about the best way to check the oil level on a diesel car. He reckoned cold was the best time but the other chap said mercedes had told him to check it hot!His newer model has no dipstick at all:needs to activate some electronic device to check his level. {sad life I lead)I get totally different readings cold...high on the dipstick.....hot....much lower, any thoughts?
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If you check it when its hot though it means you've only just switched the engine off and the oil will still be draining back to the sump and it will look like you have no oil in the engine and you'll pour a couple of litres in it and overfill it which can't be good for the engine!
Seems strange thing to do to go and drive round for half hour or so to get the engine nice and hot just to check the oil!
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In the owner's book for my BMW diesel, it says check when at operating temperature, but wait for two minutes for the oil to drain back to the sump, and also says there's no need to check, as it is done automatically, but I still check it manually!
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Be very careful about overfilling a diesel. If there is too much oil a hot engine can start sucking it up past the pistons and burning it, engine runs out of control, could eventually blow up.
Seen this happen twice, not pretty
Alyn Beattie
I'm sane, it's the rest of the world that's mad.
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Don't care what it is, car, motorbike, Queen Mary II, check it when the engine's cold.
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Unless you're checking the ATF (auto 'box) in a 123 Mercedes where (on mine at least) the instructions are to run to operating temperature; then sit in 'N' for 2 minutes, then in 'P' for one minute and then you may check it.
'til I found that out, goodness only knows what I was chekcing.
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Yes, and being new to ATF I find it difficult to actually see where the fluid level is on the stick as it all seams to merge into the background. Not like engine oil. Any tips ?
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Don't care what it is, car, motorbike, Queen Mary II, check it when the engine's cold.
on the Queen Mary II does that mean stopping the engines in mid Atlantic so they can check the oil levels?? ;-)
seriously I once had a diesel engined Vectra run away with me because a mechanic had overfilled the oil at the service the previous day. Interesting feeling when the car starts accelerating with your foot off the accelerator pedal. Luckily the road (M40) wasn't busy at the time.
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After many years of checking oil levels when the engine was stone cold I noted that the owner's manual that came with my wife's new Corsa says always check oil levels with the engine hot but after its been standing for approx. 5 to 10 minutes, but no longer than that. After 15 years of Mk3 Cavalier ownership I decided to check the owner's manual for the Cavalier and blow me it says the same thing as the Corsa! I still check the levels cold as I can't see why you would want to check them hot and risk some oil still being in the upper parts of the engine.
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If checking whilst hot, you have to be very careful about burning yourself. The oil gets very hot, and has a high specific heat capacity, so retains heat well. I was checking mine whilst quite hot once, and some dribbled off the dipstick onto my hand, not very pleasant!
Also, I wouldnt think it matters that much whether the oil is hot or not. Admittedly, the hot oil will have higher volume than cold, but not by much. And the marks on the dipstick are vaig anyway, so I wouldnt worry!
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Hot or cold doesn't matter much (oil only expands by a couple of percent between 0-100 deg.) so long as you leave it 5 mins to drain back into sump if hot.
ATF is different because the engine must be running (so torque convertor and valve body are full of fluid) - also fluid volume is large (often 10+ litres) so expanded volume is correspondingly larger.
Worst thing is to start a cold engine for just a minute or so and then take the level. A lot of cold thick oil will be at the top of the engine.
If you can't see ATF on dipstick then carefully 'touch' it against some white kitchen tissue and note the red stain which will highlight where the fluid is.
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