low oil pressure - PeachParts Mercedes-Benz Forum

adrenelin500 · #1 06-19-2006, 01:20 PM

I've looked around for a post that discusses a simulair problem with oil pressure loss but haven't had much luck, so I guess I'll be the fisrt on this subject. My 82 300 SD gets pretty hot sometimes (90-95) degrees actually it's pretty common for it to go to 90. When it get's to 60 the pressure starts to drop from (2) and by the time it gets to 90 degrees it down to (0).I just added a bottle of lucas and if anything it slowed down the graduation from 2 to 0 , but by no means has it kept my pressure from bottoming out.Can anyone lead me down the right path.

Maroon 300D · #2 06-19-2006, 01:22 PM

I wouldn't drive it again until you get it figured out! It doesn't sound like a gauge problem to me.

I wish I could shed some light on the issue. I'm sure someone else will be able to help, though.

adrenelin500 · #3 06-19-2006, 01:42 PM

I left out the part where the pressure drops to 0 when" idleing in park "after driving for a while.

bhanson · #4 06-19-2006, 01:51 PM

Engine could be running even hotter than you think, or oil pump might be going. Does it use a lot of oil? My guage is always pegged, except when hot at idle, when it drops down to a little over two maybe.
Ben

adrenelin500 · #5 06-19-2006, 01:59 PM

I rarely have to add any oil , maybe a 1/4 litre between oil changes if any at all.

barry123400 · #6 06-19-2006, 01:59 PM

Go into the archives and find the articles about what happens if the rubber washers on the oil filter canister stalk are bad. I do not remember the exact details but worth checking out I believe. Simple stuff first. There is also a real long shot that the oil pressure sensor might have become defective after it gets hot but that is so long a shot almost to be nonexistant. Usually when an engines oil pressure goes to zero the top of the engine gets a little noisier. I would not count on that either with a 617 engine. It"s pretty noisey with oil pressure.

ConnClark · #7 06-19-2006, 02:15 PM

This is bad news, don't drive the car until you get it fixed. If this was a sudden change then your in luck, if not you need another engine or a rebuild. It is definitly thermal related and I seriously doubt it is all bearing wear. On a cold start the pressure gauge should be pegged.

rrgrassi · #8 06-19-2006, 01:59 PM

Are you using diesel certified oil? As oil gets hot it gets thinner, resulting in less pressure. Ask any HD rider in hot weather what happens to them when idling in traffic in a 95 degree or hotter day.

aklim · #9 06-19-2006, 07:49 PM

I had a 91 MB that got low oil pressure too. At idle it would be half a bar and then went to 0 bar. changed the sender and got normal pressure.

Brian Carlton · #10 07-31-2006, 10:34 PM

Quote:

Originally Posted by adrenelin500

When it get's to 60 the pressure starts to drop from (2) and by the time it gets to 90 degrees it down to (0).

I'm going to make the assumption that you did not pull the vehicle over to the side of the road when the pressure dropped below .5........correct?

And, you probably drove it at 60 mph for several miles with the gauge on "0".

If this is the situation, and the engine is still running, then you have successfully diagnosed your problem. Change the oil pressure sending unit and the problem will be cured.

If, however, none of the above occurred, then more analysis is needed to determine why you have low pressure on the guage.

Hatterasguy · #11 07-31-2006, 10:37 PM

Also if the oil pressure is really 0 you should hear it. Even with a 617. I know on a 603 the lifters would be going nuts!

Brian Carlton · #12 07-31-2006, 10:39 PM

Quote:

Originally Posted by Hatterasguy

Also if the oil pressure is really 0 you should hear it. Even with a 617. I know on a 603 the lifters would be going nuts!

The lifters and the upper end of a 603 starts to really offer a racket with full oil pressure on the gauge (3.0) and the oil level at three quarts below the full mark.

The logic of this escapes me, but, clearly, the gauge reading is not the oil pressure in the head.

Hatterasguy · #13 07-31-2006, 10:44 PM

Ever pull the oil cap and see if you are getting oil up there when its that low? The oil pressure guage must not be the most accurite.

Brian Carlton · #14 07-31-2006, 10:45 PM

Quote:

Originally Posted by Hatterasguy

Ever pull the oil cap and see if you are getting oil up there when its that low? The oil pressure guage must not be the most accurite.

I don't need to pull the cap........I can hear it clearly.........there's not enough oil in the head at that point.

The gauge is accurate for the point where it's sensing the pressure, however, the pressure in the head must be significantly less.