Hello everyone,
I had a strange problem on Tuesday, at least I think I did. I was going on the freeway and it was congested. I had to drive slow, 35 and below, for at least 25 minutes. Then the trafic cleared up and I took my 123 to 70 or 75 mph. I looked down at the oil gage after a couple of seconds and noticed that the oil pressure was at 40 psi, and not pegged as it should be. I imediatly droped down to about 55 and the next time I had a chance to look at the oil gage it was back in the pegged position. I took it easy untill I got to school, about 5 minutes of driving.
I checked the oil and it was right at the minimum.
On the way back I accelerated to 70 and kept looking at the gage constantly. No problem, oil pressure stayed pegged.
The only other strange thing I have noticed is that my oil pressure reading sometimes stays at 35-40 psi when I am at idle. The normal pressure at idle is usually about 20 psi.
Do I have a problem on my hands?
Has anyone experianced this before?

Sorry about the long post, I am really woried.

Mark.

Sounds normal. You don't really have to worry unless the pressere goes down to like 5 or 10 and does not come up to peg the guage when you reve the motor up. With 30 or 40 pounds in the situation you describe, no problem.

Good luck,

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Larry Bible
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

It is natural for your oil pressure to drop during idling specially after a long hot summer drive and for as long as your oil pressure hits the maximum during acceleration then there is nothing to worry. However, I did experience a drop in oil pressure after a long drive and during accelaration it struggled to hit the max. This prompted me to check the oil pressure sensor which is attached beside the oilfilter housing. Fortunately I was right!

Looks like I was not clear on what happened.
I was going 70 or 75 mph and the gage was showing only 40 psi. The needle was not pegged. Only when I droped down to 55 mph did the needle go to the pegged position.
Thanks for all the replies. I will keep my eye on the needle and if this problem happens again I will start to investigate.
Mark.

My first thought is that the engine is either low on oil, or there is restriction somewhere around the pick up, like maybe heavy sludge buildup.

Has this car had frequent oil changes, is it used for a lot of short hops?

Good luck,

------------------
Larry Bible
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles

Another possibility is that the gauge needle is sticking at 40 psi. This would explain why it sometimes shows a low reading of 40 when you are at freeway speed, and also sometimes shows a high reading of 40 when idling. Next time it shows 40 inappropriately, give the top of the dash a slap with your hand and see if the needle springs to the normal pressure reading. If it does, you've found your problem. If not, I would replace the gauge sending unit and see if that solves the problem. Good luck!