Check oil cold or hot OM603?

[d215yq]

Well I thought I had an overly sensitive low oil light because it starts intermittently coming on when the level hits half. But then I was always checking it when hot (10 minutes after swithcing off) as I've always done on any car. This time I checked it when cold and it was on the minimum. At first I thought it was leaking it and I'd messed up my oil change but then when hot in same parking space back up to half.

I know oil expands when hot but wasn't expecting it to go min to half and the internet says some cars are calibrated for cold and some hot. So what should I be aiming for? 3/4 full when hot (just enough to get the light to stop coming on or 3/4 full when cold so no light coming on in a few k miles and nowehere near minimum but meaning it would go above max when hot?

 

[Yugguy]

I'm guessing it is not a physical dipstick? As a general rule oil should always be checked cold for two reasons, 1 so you know all the oil is back in the sump, 2 you dont have to worry about heat expansion when you dont know exactly how hot it is.

If oil light comes on when running though, then unless you are VERY low on oil your oil pump may be on its way out

 

[d215yq]

I'm guessing it is not a physical dipstick? As a general rule oil should always be checked cold for two reasons, 1 so you know all the oil is back in the sump, 2 you dont have to worry about heat expansion when you dont know exactly how hot it is.

If oil light comes on when running though, then unless you are VERY low on oil your oil pump may be on its way out

Old school 1987 physical dipstick here and old school light that comes on and off when getting low depending on going up or down hills...I've ran it 3 months 6k miles with the light coming on and off as was half when checked hot, though now see this is near minimum when cold so fits with your advice re use cold level.

Not sure if these lights only come on when very low though - the light is yellow and therefore "as long as there is oil pressure engine can continue to be ran with the low warning light on". Oil pressure is good (3 bar when cold idle, 2bar hot idle) so does that mean the pump is fine? The washer jet light comes on when it's a third full and there's 1,5 litres in there so maybe this is similarly prudent.

 

[Yugguy]

Others may know more about the model but I've been driving since 1987 and the only time I've seen an oil light come on is when either there is no oil or the pump is dodgy.

That said if you think the pump is fine and the physical stick shows enough oil then it could well be just the light.

 

[John Laidlaw]

Or the light is faulty

 

[d215yq]

The oil light (according to the blurb) is yellow and comes on when the oil is reaching minimum - as long as there's oil pressure car can be given so it's not the red light where it meets an absolute minimum meaning stop on some cars. Indeed I thought the light was faulty it's been driven off and on with the light coming on for many months with no problem.

It's just having seen how much lower the reading is when cold maybe I'm wrong to check it hot and the light is indeed correct as it comes on when the oil is just above the min mark. So either the light is faulty and the hot reading is what matters or the light is correct and I just need to go off the cold reading and add some oil...I'd prefer to put more oil in it so the light disappears but then don't want to over fill it.

Surprised it makes so much difference but I suppose it does take 7.5L of oil so expansion/contraction has more of an effect

 

[stwat]

Others may know more about the model but I've been driving since 1987 and the only time I've seen an oil light come on is when either there is no oil or the pump is dodgy.

That said if you think the pump is fine and the physical stick shows enough oil then it could well be just the light.

Its an oil level light not oil pressure. This is from the good old days when they had an oil pressure gauge and a low oil level light which illuminates when the level is at around half way on the dipstick.

 

[d215yq]

Its an oil level light not oil pressure. This is from the good old days when they had an oil pressure gauge and a low oil level light which illuminates when the level is at around half way on the dipstick.

Thanks for clarifying - that's when the light comes on. It seems a bit over the top to come on at half way and not the minimum but the washer jet one does the same. I suppose to give plenty of warning and not interrupt a journey! I'll put in half a litre of oil and be done with it

 

[hotrodder]

http://www.w124performance.com/service/Index/602_603/18Lubrication.htm 18-225 (near the bottom of the pg) describes how the oil level float works. It's not supposed to light up unless the oil level drops somewhere near min. The level gauge in my 320te (exactly the same level sensor, a1245420017) is sometimes pessimistic too (flickering or lighting up occasionally) when the oil level is fine according to the dipstick

Don't overfill it to avoid being annoyed/worried by the level warning... the max mark on the dipstick is an absolute max, not a target. Dunno about the earlier diesels but for the m104 engine in mine the oil capacity was apparrently reduced by 0.5 litre due to the potential for oil leaks if brimmed i.e. making the max mark overfilled (difference between min & max on the dipstick is 2 litres on mine) http://www.w124performance.com/service/Index/Resources/00.57EngineOilLevelSI.pdf