Patrick Frye

Guys, i really need help here. I have searched for hours on the mercedesshop forum looking for clues to help with my 86 300sdl to no avail. The motor has low oil pressure. I bought the car last summer and have since changed the oil to straight sae 30 and also changed the pressure sensor. Upon starting cold, the guage usually pegs and graudally comes down during the drive like normal but it will get very low at idle sometimes (scary). The lowest point i have seen is about .4-.5 bar after a run on the highway at 75. Before i changed the pressure sensor, the needle would be resting on the 0 pin!!! I kind of knew the motor had some pressure as it sounded and ran ok. This is my first 603 car, and all of the 617's ive had will maintain 1.5bar or so after a highway trip regardless. Yesterday morning when i started up cold (its getting warmer here in new orleans now... it was probably 75 degrees), it would only muster about a 2.5 or so. Also, i am getting some lifter tapping (sounds like 1 or mabye 2) at any time, but usually worse when cold. Its not horribly loud, but certainly identifyable. The motor has probably 300k miles, but makes great power, doesnt overheat at all, and consumes no more than one quart per month and this is a daily driver with lots of highway. My questions are: is there a pressure relief valve in the block or the pump that could be stuck? Does it sound like the pump's worn and in need of replacement? Is it the bearings in the motor that are the problem (i really doubt this one as it runs so good). I have found an NOS MB pump for about 300... is this a good deal? Should i do the lifters at the same time? Any help or suggestions would be appreciated very much. I just dont know what to do or where to start!!!
Patrick

TMAllison

I'd suspect you will get more constructive info on possible problems on the other forum.

A comp or leak down test might be in order. There is a point at whihc a diesel will need valve or ring work to keep making comp. 300K is "somewhere" around that point for the avg engine. They don't go 500k without *help* usually.

Have you tried a heavier oil? A qt a month is meaningless; could be 10 miles or 10k miles. Lots of folks use 1qt/5-600 miles as a cut off for a valve job or rebuild.

Patrick Frye

well, the odometer quit.. so i am unable to accurately document the oil consumption. I would say that i drive an avarage amount, so it probably consumes 1 qt per 1000-1250miles. In any event, it seems to consume far less than other mb's ive owned with 617 motors. It does sound that you are leaning toward overall wear as the probable cause for the low oil pressure. correct?

Ausmbtech

Remove the oil filter and replace the 2 orings on the bottoom of the shaft that runs though the oil filter. Part number A015 997 94 48 (x2) these aren't supplied with the oil filter and rarely get replaced yet can cause many oil pressure problems. Definately worth trying first.

As long as your oil pressure reaches 3bar when over 1500rpm and at least 0.5bar at hot idle I wouldn't be too concerned about it.