Question for 500SL drivers - PeachParts Mercedes-Benz Forum

Sid The Kid · #1 03-08-2004, 03:04 PM

I have a 1991 500SL with about 120K's on the clock. When the car is in drive or reverse at dile i will hear rattling/clicking sounds coming from the engine. As soon as I press the gas or let the car idle in neutral or park the sound will go away. So basically I only hear this noise under light rpm. Does anyone else's engine make the same noise as mine?

Sid The Kid · #2 03-08-2004, 06:12 PM

............

Pete Geither · #3 03-08-2004, 06:29 PM

Nope

Fast Eddie · #4 03-09-2004, 07:32 AM

Could it be the timing chain or timing chain tensioner? Should be changed at 100k miles.

Mike G · #5 03-09-2004, 10:57 AM

Sounds like an exhaust rattle. If it was the engine, it would do it in neutral also.

Sid The Kid · #6 03-09-2004, 05:02 PM

thanx for the replies. I counted out the timing chain becuase the noise is coming from the sides of teh engine where the tappets are. do any of your cars make any tappet noise at all??
i think the noise is still there but when u put it in neutral the increased rpm drowns out the sound. just a guess? and with tappes they make a sewing maching sound. this sound i get is not as constant. sometiems ull get 3 clicks in 5 seconds or sometimes ull get 2 clicks in 5 seconds. it varies. if its the exhaust where should i look?

bwheitman · #7 03-09-2004, 05:46 PM

hmmm My little SL was making some racket while in gear, reverse or drive while moving in and out of the garage at slow speed, It was coming from under the car and sounding like a swishing and and a grunting sound. It turned out to be the transmission fluid, I don't know how, but they said at the dealer that the transmission gets noisy when it needs changed. I would recommend that you check your motor mounts for wear, there could be a rattle on a heat shield while in gear because the engine is under torque and therefore clearances change. If the engine runs fine otherwise have someone put it in gear (that you trust) while you watch the engine and see how much it moves when the gear is engaged. This is just a place to start, but it might help. After that I would then check the chain, if it has not been replaced yet that is very likely. Take it to a dealer and have it diagnosed, sometimes the money you pay for a diagnoses is well worth it rather than chasing a problem you will never find. My car would go into limp mode once in awhile when it was rainy out, I threw parts at it, still no fix, finally took it in and it was the plug boots under the coils arcing. Any cross will cause the computer to set it into limp mode. Good luck!
Brian

bwheitman · #8 03-09-2004, 05:50 PM

Oh I forgot to mention, to chase down a noise you can take a long wrench and hold it close to your ear with your hand, place the other end on the area you want to listen to. check the timing cover then the head covers, you can pretty much tell where a noise is coming from, if it is coming from your head covers go get some new seals and remove them. Take a look at the lobes on your cams you could have wear causing the tap tap you are hearing. This is a rare occurance but a possibility. Just some ideas.
Brian

Sid The Kid · #9 03-09-2004, 06:08 PM

Thanx very much Brian you have been very helpful. I just changed the transmission fluid (4 drain and fills over 10K) and from what you have said the exhasut does seem to be a possibility.
You also mentioned something about limp mode, with this, do you mean when u take a corner and then all of a sudden the car is stuck in a very low gear and doesnt seem to move but then all of a sudden will get its power back. That happens to me about once a week.

tecqboy · #10 03-09-2004, 11:05 PM

A long shot..... Fuel pump relay. But only if it clicks, they don't rattle.

Mike G · #11 03-10-2004, 09:35 AM

Exhaust rattles seem to vary more than engine noises. An engine noise will always be there. It will follow rpm -- so more rpm -- higher frequency. Exhaust rattles vary with rpm -- but the variation is not as linear and tends to happen only at certain, usually low, rpm. This is partly because engine has different harmonic vibration at lower rpms. I look for exhaust rattles by lightly poking around underneath (from the side) with a wooden stick while car is running. More often than not, its an exhaust shield or a bad cat converter.

MG

bwheitman · #12 03-10-2004, 09:45 AM

Sid,
the limp mode is when the engine detects a misfire or a critical malfunction and will "turn off" cylinders. I think it only runs on a couple of cylinders, so that you can limp home. This can be remedied by turning your engine off and restarting it, although your check engine light will stay on until reset. The fact that your transmission falls into a lower gear at a turn sounds correct if dependant on speed, but what you describe seems more like a slip due to fluid movement. My car acted kind of funny when I first got it about 6 months ago, the car would have a delay when you put it into drive, and would behave funny when I was hot-rodding, you know playing around like a kid! turns out when I went to get the fluid changed I was low on fluid. I am not saying this is what is wrong with yours, but have it checked at the dealership, I was reading my dipstick wrong, and I think your transmission is sealed with no dipstick? I have an SL320, but I think the 500's were sealed up. Well good luck!
Brian