1982 240D Euro idle & oil pressure - PeachParts Mercedes-Benz Forum

indybenz · #1 05-18-2023, 10:19 AM

Hello,

Anyone help with this one? Here are two videos.

Ever since I replaced the head gasket, which included replacing the front crank seal and water pump and a few other bits, the oil pressure drops randomly at idle, usually after it's warmed up. Then lately the idle will also fluctuate, sometimes in sync with the oil pressure but other times the oil pressure will stay at 3 bar and the idle will drop very low and almost stall.

Hopefully these videos will play
https://photobucket.com/u/northy_polk/a/130a4e88-2b57-41af-a8da-daaae7b03ead/p/5272c917-6553-426f-881e-12212de3f90d
https://photobucket.com/u/northy_polk/a/130a4e88-2b57-41af-a8da-daaae7b03ead/p/5272c917-6553-426f-881e-12212de3f90d

Sugar Bear · #2 05-18-2023, 02:44 PM

What is the ambient air temperature? What weight oil?

1 bar oil pressure at hot idle is common. The gauge should peg as soon as it is accelerated.

Good luck!!!

t walgamuth · #3 05-19-2023, 11:09 PM

verify oil supply in engine.

indybenz · #4 05-24-2023, 11:10 AM

Quote:

Originally Posted by Sugar Bear

What is the ambient air temperature? What weight oil?

1 bar oil pressure at hot idle is common. The gauge should peg as soon as it is accelerated.

Good luck!!!

Not sure the exact temp but it fluctuates this time of year in Indiana 50-80F. The air temp does not seem to have any impact one way or the other. The engine temp, however, does seem to have an impact. When it is warmer the oil pressure and idle are both more erratic.

The oil pressure is always at 3 under load, but at idle it varies from 1.5-3 and goes up and down erratically.

Oil is 15w40 of some sort. I change the oil frequently and often get what is cheapest 15w40.

indybenz · #5 05-24-2023, 11:11 AM

Quote:

Originally Posted by t walgamuth

verify oil supply in engine.

There is oil in there.

indybenz · #6 06-06-2023, 09:29 AM

The car still has this surging/dropping idle issue. Anyone else care to take a guess? The videos in the first post show from outside and inside. Thanks!

*UPDATED the links so hopefully vids will play now

hercules · #7 06-09-2023, 08:17 PM

Pop off linkage to injection pump, ck. if pump is on stop.
Ck. fuel pressure.
How much fuel is in tank?
Fuel lines connected to proper places.
Oil by pass valve could be sticky
Water in fuel or algae blocking fuel strainer.
injection pump inner adjustments.

Diesel911 · #8 06-10-2023, 01:55 AM

1.5 bar at hot idle is an OK oil pressure in the factory service manual.

The question is it the engine speed that is causing the fluctuation or is the engine speed reacting to some load that the oil supply system is putting on it and bogging the engine down.

Way back in 2007 when I first became a member, I believe I read something about sticking oil pressure relief valves in the oil pumps. I also read the relive valve springs occasional break.

If you have an oil cooler there is a thermostat in the oil filter housing as well as the mentioned oil bypass valve.

The fuel pressure relief/overflow valve controls the fuel supply pressure. In time the springs become weak, and they don't hold pressure well at idle speeds. Also, a ball bearing is used as a valve. If here are rough or rusty portions on the ball, you get erratic fuel pressure.

The fuel supply/lift pump on 240Ds have disc valves in them. It could be they are worn there is build up on the tiny springs.

Air leaks can cause surging as well as the mentioned clogged filtration to include the tank screen.

indybenz · #9 06-13-2023, 11:16 AM

Ooft.

Looks like I have some investigating to do.
1. fuel pressure relief/overflow valve controls the fuel supply pressure
2. oil pressure relief valves
3. air leaks are unlikely from my experience but won't rule that out
4. I put a larger capacity fuel filter on and eliminated the small 'primary' fuel filter and the problems started after that so perhaps should go back to the original set up.