Oil Pump - rebuild, replace, or live with it? - PeachParts Mercedes-Benz Forum

lonewolftek · #1 04-17-2007, 12:41 PM

I've been having issues with the oil pressure in my 300SD. At hot idle (500 rpm), it drops below 1 bar, sometimes as low as 0 bar if it's a very warm day. Cold idle is still 3 bar, and above 1000 rpm it rises rapidly to 2.5 bar or higher. Popping the filler cap off, I can see the valvetrain being lubed at idle or while revving the engine. Haven't heard any abnormal noises to suggest parts not getting lubed up.

I've changed o-rings, filters, brands and types of oil, and finally replaced the sump pan and seal. The mechanics I've had look at it have said it's normal for an engine approaching a half-million kilometers to have low idle oil pressure due to the pump wearing out.

My question to the collective wisdom is, are they right? Is this
just the oil pump getting old? From the look of the old sump pan, it took a hit at some point, had a big dent at the front and the entire lower surface was pushed up some, possibly enough to hit the bottom of the pump.

Is rebuilding an oil pump something that is possible on these 617 engines? Or should I be saving for a replacement, and driving my other vehicle instead of the Benz?

carnut · #2 04-17-2007, 01:40 PM

You are getting way ahead of yourself. First verify oil pressure with another gauge. Buy/borrow an oil pressure gauge and install it. Compare your gauge to the added one and report back. Could be as simple as a faulty gauge. Verify, verify then repair and/ or replace.

regsatx · #3 04-17-2007, 01:45 PM

My 85 SD is happy idling at 750-800 rpm. Your oil pressure reading and overall performance will be better at a higher idle speed.

Good Luck

rrgrassi · #4 04-17-2007, 02:10 PM

Does the Oil Pressure begin to peg as the RPM increases from idle to around 1500? If so, pump should be fine. Could also be a bad guage or bad sending unit. Again, as stated, verify verify verify before repair.

vstech · #5 04-17-2007, 03:09 PM

don't forget that the SD OP gauge is electrical, not mechanical, so the sending unit could easily be on it's way out. 500 is a little low of an idle, too.
John

Ken300D · #6 04-17-2007, 03:37 PM

The oil you are using also has some impact.

You'll get different oil pressure behavior depending on whether you are using 5w-30 or 15w-40, etc. So, you may get additional feedback if you tell us what motor oil you use in the car.

Mercedes gauges are not scientific instruments. They are just indicators.

Ken300D

CarFax = $25 for 30 days. Autocheck = $25 for 60 days. Which do you prefer?

pawoSD · #7 04-17-2007, 03:46 PM

Mine registered a flat 0bar the other day after going on the freeway for an hour. And it twitters and jumps around when slowing down. Sender is probably almost dead. Still pegs when I rev the engine though. If it completely dies I'll replace it. I obviously have oil pressure, as I've looked and seen the jets in the valve cover, and when it was at 0 bar, I sat idling a good 10 mins that way....I suspect I'd have heard something right away.