Oil Presure Worries

[iamamanc]

Hi took it (94 W124 300d OM606) for a spin this morning to see if what I have done so far has altered anything;
I noticed that when cruising at about 50mph the oil pressure drops to about 2 1/4 and when I stop at lights it drops to about 1 1/2. As soon as I toe the gas it shoots back up to 3 untill I start cruising again. Be it 30 40 or 50 mph it always drops to about 2 1/2 - 2 3/4. As I said when I apply the gas (put a load on the engine) it shoots back up to 3. Can anyone reccomend an oil additive to help clean up any sludge in the lines
Checked oil level - ok. Nice and clean no gunk or froth on the cap.
Checked Water resevoir - Clean no bubbles or oil

My other 300D doesn`t have the drastic differences, this is the reason I am concerned - the comparison
Should I be worried

Cheers

 

[oigle]

Your oil pressure is strictly related to temperature, engine revolutions and SAE viscosity of the engine oil. Cold oil, and the pressure will maximise to 3 bar (about 43psi), controlled by a relief valve in the oil pump. When hot, the oil thins and the pressure drops if the revs are not high- ie at idle or low cruising revs. Thus 2 - 2.5 bar is normal - less at idle. When you "give it the gas", you are not increasing the oil pressure by "loading the engine". It is simply a product of higher engine revs.
A good quality diesel oil is quite good enough to remove sludge and keep it at bay. Additives are totally unneccessary.
In answer to your question - I wouldn't be worried at all.

 

[Parrot of Doom]

Oil pressure should rise when you floor it.

Check your oil pressure sender anyway.

 

[iamamanc]

Cheers for that, it's a weight off my mind. When we strip it to do the timing chain everything will get a good looking at
Cheers

 

[sdc77]

Why?

Why are you doing the timing chain?

 

[Mikesmerc]

Are the timing chain tensioners on this model dependent on oil pressure?, I have heard of faulty tensioners leaking too much oil past their seals and creating a low oil pressure reading. I would have thought that you should have a full oil pressure reading at 50mph. The reason I say this is that every old Mercedes I have owned up to the early 90s diesel and petrol have had full oil pressure at 50mph even the the ones with almost 200,000 on the clock. I suppose its down to how well they were maintained before I bought them. I do miss the oil pressure guage on later cars.
Regards
Mike

 

[sdc77]

tensioners

Yes the chain tensioner on my 300d relies on oil pressure..
In fact it has to be primed before you replace it.

at cold and when warm my oil pressure is at 3 at anything over 1500 rpm

Once hot.. on tickover it will drop to 2 - 2.5 at under 2000 rpm and 1-1.5 at tickover always returning easily to 3 at touch of the throttle.

Its got mobil 1 in it.. Im considering changing this to castrol on the next change.. wonder if this will affect the pressure.

 

[Mikesmerc]

That sounds about right SDC77, changed from fully sythetic to standard once on my 1990 560sec and it improved pressure slightly and quietened the tappets.
Rgds
Mike

 

[television]

I would not worry over the oil pressure, there are always a slight difference between cars and several things as mentioned can make small differences plus the presure is adjustable by putting washers in the relief valve, as they are set up when new.

Malcolm