Load low moaning sound at idle hot or cold- what the heck? - PeachParts Mercedes-Benz Forum

bodyart27 · #1 09-13-2003, 10:09 AM

1984 300SD - 182.5K mi

When I got the car about 2K mi ago, I went through the car and changed all the fluids and filters and sometimes I'd get a very audible and fairly load moan / groan like old pipes, a humpback whale, or something. I thought it was air in the fluids but I can't find anything foaming in power steering, brakes or coolant. I’ve put on over 1Kmi so I would think air in the coolant should have worked it’s way out. The car is not running hot. On a cool day just a tad over 80*C, very hot day with A/C maybe 90* but never gets scary (though the A/C might not blow as cold). I also replaced coolant hoses and the thermostat.

At first it seemed that this was occurring after startup and short periods of idling or very little driving. The moan is not a constant predictable thing. I can’t make it happen and it ends after about 20-30sec - just before I can pretty much get unbuckled, pop the hood, jump out of the car and get my ear over the engine bay, it's all over.

From inside the car, it’s loud and coming pretty much dead center of the dash. I've pumped brakes, idled forward in gear, pulled it out of gear, turned the steering wheel back and forth, and revved the engine. Nothing seems to impact the moaning volume, tone or reduce the amount of time or eliminate these moaning cycles. When it's done it just stops.

It hasn't resurfaced too much in the past 30 days, but I had exited the freeway in the rain this week and was idling at a light and it started moaning again (so the car was plenty hot). I kept looking right and left to see if the other folks in traffic could hear it. It really is an embarrassing sound. It happened again the next day so I'm trying to figure out what the heck this might be.

Any thoughts?

psfred · #2 09-13-2003, 08:21 PM

Most likely a vac leak -- check to see if it is related to AC servo selection (ie blowing out the dash vents) and goes away if you turn the temp control to heat (floor vents). If so, you need to replace the affected (or all) vac servos in the climate control system.

The other obvious thing is a bad or loose power steering belt -- they groan something terrible when loose. The worst is in the case like the 280, where there is a double belt and they are no longer available in matched sets, so one is always looser than the other. Groans terribly sometimes.

Peter

bodyart27 · #3 09-14-2003, 09:49 AM

I just had a bunch of A/C work, but the sound was there before and after. I'm not sure if they checked all the vac points behind the dash, but the vents do regulate well by themselves..... but something to consider.

I have NOT replaced the belts (they had looked pretty good). I'll go give them a good wiggle and see if I have play on the p/s pump.

Belts are on the eventual list of stuff to go after... timing chain, valve adjustment, braided fuel lines by injectors, belts.... always something.