Low Oil Pressure - PeachParts Mercedes-Benz Forum

RUYSENAARS · #1 05-06-2003, 01:28 PM

HAVE 83 300D TURBO. WHEN HOT I HAVE .2 BARS OIL PRESSURE. CHECKED GAUGE. SEEMS OK. REPLACED RODS AND MAINS. NO DIFFERENCE?? I USE 20 W 5O SYNTHETIC, AND TRIED 30 ROTELLA T. I AM TOTALY STUMMPED!!!!! ANYONE HELP!! I ALSO CHANGED OIL PUMP. STILL NO DIFFERENCE. SHES EATN ALL MY MONEY. LOL!

P.E.Haiges · #2 05-06-2003, 09:44 PM

Ruysenaars,

There is a oil pressure relief valve that is designed to maintain the oil pressure at 3 bar maximum. It is a ball valve with a spring behind it. The ball is forced off its seat when oil pressure exceeds maximim and the overflow oil is returned internally to the crankcase which reduces the oil pressure..

Possibly the spring broke or the ball is stuck open.

I would check the above before anything else. I'm not sure where it is on your engine, but I think it is on the front. Check in a repair manual to find it. Or maybe someone else here can tell you where its located.

P E H

JimSmith · #3 05-06-2003, 10:52 PM

RUYSENAARS,

Is this condition while you are at idle or when the engine is under load? Jim

RUYSENAARS · #4 05-06-2003, 11:17 PM

ONLY AT IDLE, WHEN HOT. AS SOON AS YOU REACH 1500RPM THE GAUGE IS PEGGED OUT.

Palangi · #5 05-06-2003, 11:26 PM

Sounds like normal operation. Check the owners manual for details.

JimSmith · #6 05-07-2003, 01:03 AM

RUYSENAARS

Like Palangi says, that is normal. As long as the pressure pegs under load you are fine. If it really spooks you it might be worth your while to increase the minimum idle speed. A Diesel will idle at a very low rpm, and is often set to idle there to save fuel. It is absolutely ok though.

Good luck, Jim

Rick Miley · #7 05-07-2003, 09:29 AM

Before we all brush this off as normal operation, let's look again at his original post. He said .2 bar pressure at idle - zero point two, or 2.3 PSI. RUYSENAARS, how did you determine this? Was it from an external gauge that is calibrated much finer than the dash gauge? Or did you mean to say that the dash gauge goes down to '2' at idle?

RUYSENAARS · #8 05-07-2003, 10:36 AM

OK TO CLEAR THINGS UP. THE "BOOK" AND "MERCEDES MECHANICS" SAYS THAT THE PROPER OIL PRESSURE, WHEN AT NORMAL OPPERATING TEMPERATURES, AT IDLE SHOULD BE NO LOWER THAN ".7" THAT IS (POINT SEVEN") IF IT IS LOWER THAN THAT THE PROPER LUBRICATION IS NOT ACHIEVED THUS WEAR BEGINS AND THE ENGINE "DIES" EVENTUALLY. TO ANSWER THE AVBOVE QUESTION, .2 BARS IS APOX. IT IS ONE NEEDLE WIDTH ABOVE ZERO.

JimSmith · #9 05-07-2003, 10:38 AM

Rick,

The manual I have from a 1984 300D (Euro model) covers 240D and 300D turbos and non-turbos. This item says 0.3 Bar is fine at idle as long as the gage pegs under load. If the rpm is a little low at idle the oil pressure will not be as high. To fix this problem I would re-iterate my previous suggestion, increase the idle speed by 50-100 rpm. It is feasible the idle speed is a little low due to wear and tear on the linkages and set point stops. On a 240D you could do this by using the little knob on the dash to the left of the steering column. On a W123 300D Turbo it is not clear to me exactly how this is done (never owned one), but I would bet a cold beer it is mechanical and can be adjusted.

Good luck, Jim

RUYSENAARS · #10 05-07-2003, 10:43 AM

WELL THANKS FOR SUGGESTION. BUT I THOUGHT OF THAT ALREADY. I DO HAVE A MERCEDES MANUAL, FROM DEALER AND IT SAYS .7 BARS. I DID ASK ABOUT HOW TO CHANGE THE IDLE SPEED, THEY SAY ON MINE IT IS IMPOSSIBLE, TO THAT I SAY BULL*&@#. SO I AM STILL TRYING TO FIND OUT HOW TO INCREASE THE IDLE SPEED. BELIEVE ME THIS IS KIKN MY ACE!

Rick Miley · #11 05-07-2003, 11:03 AM

Well, now we've got this thread going again. Idle speed not adjustable? I'm with you - bullpoo. Does it sound like it's idling low? And does a tiny increase via the accelerator raise the pressure into the correct range?

Jim - thanks for chiming back in. Hope I didn't ruffle your feathers, just wanted to make sure his post was being read properly.

RUYSENAARS - please turn off your caps lock. All caps on the internet is interpreted as yelling, which will offend some people.

That .2 still sounds pretty scary. My 240D is showing about 1.5 at idle.

P.E.Haiges · #12 05-07-2003, 11:12 AM

Ruysenaars,

When I read your original post about the 0.2 bar oil pressure, you said nothing about the oil pressure increasing with engine speed. So my diagnoisis of a bad oil relief valve was not applicable because it is not valid if the oil pressure increases with engine speed of which you mentioned nothing.

I had an old 190D MB that had almost the same problem. However it ran for years in that condition. So maybe the solution is to do nothing or use a heavier weight oil.

P E H

JimSmith · #13 05-07-2003, 12:07 PM

Rick,

No ruffled feathers. They are glued to my skin so it is pretty hard to ruffle them.

RUYSENAARS,

Is the 0.2 Bar something that happens in drive or neutral? And no idle speed adjustment? That is hard to swallow. I just read the instructions for the 240D and 300D (non-turbo) and they are pretty straight forward. I am having a hard time believing the 300D turbo has no adjustment provisions.

Good luck, Jim

RUYSENAARS · #14 05-07-2003, 12:09 PM

Ohh. my bad, sorry about the caps, no ruffled feathers here!!! I tell you though this sure has got my goose!!!! I want to get all the details lined out though, so I was trying to be precise. Ok well to answer your question, it does idle about 750rpm, and just a slight increase to perhaps 850 rpm will bring the pressure to where it should be. It does feel like the car should idle faster, there is alot of shaking at idle. More-so than I believe it should, thought it was engine mounts and engine shock, but they are new too. Soooo, my unexpert opinion is that just a slight increase in idle speed would soothe my concerns into soft iceream.... but that leaves us still the problem, how to increase the idle. There is an adjustment in throttle linkage, but have adjusted to no avail. There is also an adjustment on the fuel pump where the throttle linkage connects. This apears to also be the adjustment for fuel cut-off. ?????????????

RUYSENAARS · #15 05-07-2003, 12:15 PM

Ohh, by the way, this was a "certified mercedes" mechanic that says there is no adjustment on this car. I did try to adjust something on my fuel pump, alomost "red lined" the car, scared the poooo out of me, so feeling a bit umm scared to try again!!