Help. High oil pressure at idle (190e 2.6)

[mosquera]

I'm a new owner of a 93' 190e 2.6.

I've noticed that as soon as turn on the car the oil pressure rises to the max 3.0 bar and simply stays there. I sort of recall this being a recent phenomenon (I've only had the car 1 month).

I've read that the oil pressure should be between the 1.0 and 1.5 bar at idle.

The car does not drive hot and the oil looks clean. According to the next oil change sticker placed by the dealer, I should still have 1,000 miles left on this oil change.

Any thoughts?

Thanks

[sixto]

That's normal if it doesn't go to 3 before the engine's running. It'll drop as the engine warms up. Make sure it stays at 3 while your driving and only drops below 3 when idling.

Sixto
91 300SE
87 300SDL
83 300SD

[Mike Richards]

The car should be at approx. 1 bar at idle after warming up. I believe the allowable value is just under 1 bar at idle once warm. The pressure should jump to 3 bar after rpms hit approx. 1500.

At highway speed the pressure will also be 3 bar.

1 bar is about 14.5 lbs. 14.5 x 3 = about what you'd see in a domestic at highway speed.

[Duke2.6]

The owner's manual says idle pressure as low as 0.3 bar is acceptable, but I've never seen mine lower than about 1.0 bar in very hot weather, and 1.5 bar at idle is normal in mild weather. These readings are with the engine at full operating temperature - at least ten to fifteen minutes of driving in mild weather. It takes some time after the coolant has reached operating temperature for the oil to reach full operating temperature.

Cold idle pressure will be higher depending on the SAE grade of oil in the sump and the ambient temperature.

Duke

[mosquera]

The indicator needle does not drop from the highest 3.0 mark even after it has warmed in idle.

Last night in between drives I noticed that the pressure dropped to the 1.0 bar at idle, however, when I turned off the car and restarted later the bar again jumped to 3.0 and stayed there at idle (not driven).

What could be the cause of exceessive oil pressure while the car is parked?

Should I be channging a part?

Thanks much all your sharing of MB knowledge is much appreciated.

[Duke2.6]

My hunch is that you have a misbehaving oil pressure sending unit. It's located just below the filter pad. You could go a ahead and replace it apriori. It's also possible that the dash gage is sticking, or it could be the oil pressure relief valve. Proper function of the pressure relieve valve can be checked with a mechanical pressure check gage,

Duke

[G-Benz]

Does it peg to "3" when you just turn the key to the "on" position (without starting the engine)?

If so, it IS the oil pressure sender.

I just replaced mine a month ago for the same quirky behavior.

Check out this thread for more info...

W124 oil pressure sender...drain oil first, easy install or not?

[mosquera]

Great tips,

I'll turn to "on" key position and post the results. While I know that I'm still in the diagnosing stage, how much does it cost to replace either:
(1) the oil pressure sending unit, or
(2) the oil pressure relief valve?

THX

[mosquera]

Sorry, one more thing.

If have to drive the car for another week or 2 without replacing either the oil pressure sending unit or the oil pressure relief valve and I'm looking at serious risk?

[mosquera]

G-Benz,

took your test advise. When I turned the key to the "on" position the oil pressure needle does not budge, however, when start the engine the needle continues to immediately rise to the top 3.O pressure mark, at idle.

Sparadically (between drives) the guage conforms and it reads in the proper 1.0 range during idle.

So do you think its still the oil pressure sender or does that result eliminate that as a cause? Tight on budget and I'd like to make the correct repair investment.

Thanks again.

[sixto]

I still don't see a problem. It should peg at 3 at cold idle. It takes oil longer to get to operating temperature than coolant so don't expect it to dip at idle right when the temp gague gets 80C.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

[G-Benz]

I agree. I think everything is normal.

From your earlier posts, I was led to believe that your gauge pegged at "3" all the time.

You should see the gauge go to "3" immediately after you start the engine. Oil is cold and thicker at that point and will read high until the engine is warmed up. After some time driving, you should see the needle fluctuate and go to a nominal position at idle.

The behavior of this gauge isn't obvious unless you've owned MBs before.

I put AutoMeter gauges in my VW and while the oil gauge is mechanical, when the oil is cold upon startup, the gauge shows very high pressure readings. The needle drops steadily as the engine warms up.

Anyway, if you think the oil gauge gives unusual readings, wait until summer hits full swing and you get to watch your temperature gauge! Don't expect the temp gauge to go to a midpoint position and stay there!

[xp190]

Change your oil pressure sending unit, I had the same thing, if you turn the ignition on to position 3, just before you start cranking the engine, and it goes to 3, it's a bad sensor.

I just replaced mine, half hour job if you got the right tools.

xp

[mosquera]

Hey Sixto,

Actually the needle stays pegged at 3 even after the car heats up in idle.

When I said sometimes it drops (between drives) I meant that I turn off the car and started again an hour later and the needle sometimes stays in the proper 1 bar range or sometimes jumps to the 3 bar.

In other words it still stays pegged at 3 after the car is warm and is in idle.

Thanks for the advice though you guys are very knowledgable.

I think that I'll just go ahead and chage the oil pressure sensor.

Could I still drive the car like this for anoth week or two before I fix the oil pressure sender...or is this dangerous?

[sixto]

I think I understand now.

If under the same circumstances it sometimes shows 1 bar and sometimes pegs, then there probably is a problem. I'd start with checking the wires that connect to the oil pressure sender. Maybe one is loose or frayed. It's hard to check the wiring into the gauge cluster but it's a relatively mild and clean environment back there.

As to whether it's safe to drive the car as is for another two weeks, that's up to you. You essentially have an unreliable gauge of one of your engine's vital signs. If it shows 3 bar when you think it should show 1 bar, it could show 3 bar when it's at zero. You have to decide how likely an event that is.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD