My 1986 300E 5-speed with 191K miles has started making a worrisome noise. I would call it a loud rattle, from the front of the engine.

Not present when cold, but very apparent when warm.

No change if turn AC on.

Increases in tempo as RPM increases.

Does not seem to be coming from cam/valves. If had to guess, loudest in lower front passenger side of engine.

Oil level and pressure are normal. Using 20-50 for summer driving.

Sometimes will diminish if I let the clutch out.

I bought this car from the original owner. Regular maintenance, but no major engine work.

TIA for ideas.

Chuck

Chuck:

Clutch throw-out bearing?

Noises are hard to isolate, from a DIY'ers point of view, one of the most useful tools is a stethoscope contraption available at the auto parts store with a long metal probe.

With engine running and all safety bases covered (no loose clothing, eye protection, etc), start touching the probe in the areas you think the sound is coming from. You should be able to find the part as it will be very obvious, only in your case you may need the help of an assistant to rev the motor and possibley have the car raised as well.

Good Luck!

Sounds familiar
 

Brother of The Benz, ctaylor738
To use a stethscope,do as many DIYers do.
Using a long bladed screwdriver, place the handle hard against your ear and the blade against the item you want to listen to. Works like a charm.
Sounds familiar.
Very commomn rattle at front of the engine is the shock absorber of the automatic belt tensioner.
This little rascal has made fools out of a great number of us.
Give a listen.
Happy Trails Beep Beep from The Spiderman in Houston!!!

An update -

I was on my way to work, planning to stop by Silver Star Motors to get Herr Fuch's opinion on the noise this morning, with a stop at the dealer to pick up a part for the '73 280C. About two blocks from the dealer the serpentine belt started making a godawful squeal below 1500 RPM. I decided that discretion was the better part of valor and pulled into the service department for help.

Should have some news shortly, but it looks like something to do with the tensioner.

Thanks to all,

Chuck

Update!
 

Turned out to be the water pump bearings, but the tech also identified timing chain noise.


I passed on the $786 for a water pump.

Chuck

I'm guessing that includes (dealership at $100/hr.) labor...that's about how much it set me back when mine gave out early this year...the actual pump goes for around $250.

I would get a second opinion. In my experience that sound is the bearing for the fan clutch. Just my opinion.

I would try rocking the polley on the water pump.If you have noticeable movement the bearings are indeed bad.

Good call Stan Pittman!

I ordered a water pump from Fastlane, and started on the job this morning. The water pump was fine, but the fan pulley bearings were gone.

So much for the diagnostic skills of American Service Center.

Located a replacement at a dealer with parts dept open on Saturday (HBL) and installation went without incident. If you do this replacement, you will probably need an updated version of the bolt that holds the fan clutch to the pulley - the new part requires a shorter one. You will also need the O-ring where the heater pipe goes into the thermostat housing.

One tip - you only need to loosen, not remove the small bolt that holds the heater pipe to the top of the bearing housing. Once loosened, you can slide the pipe to the left and proceed with the removal.

Chuck


This also seems to have cleared up the suspected chain noise.

Whoopie for you
 

Brother of the Benz, Chuck
See how great you feel after a successful Saturday under the Shade Tree?
Happy Trails Beep Beep from The Spiderman in Houston!!!

Chuck,

From now on, go to:

Autobahn Service Center (in Rockville)
http://www.autobahnsc.com
301-881-1310

You won't be disappointed.


Eric

ctaylor738,

I have just noticed unusual noise in my 350 SDL, and on troubleshooting noticed what I think is abnormal play by holding fan blade assembly and flexing it against shaft ... looks like it is the shaft from the fan blade assembly to the viscous coupling ... does you E have this sort of a set up, too?

With 130K on it, I guess I do need to replace the pump, too ... how about the thermostat? Since it is all apart, guess it makes sense to replace?

I'm in Fairfax Station ... have been through ASC several times and have never been exactly overwhelmed by anything ... lots of talk ... greatest line was from their lead used car salesman who stated that "among the MB dealers in the area they were the Nordstrom dealership."

Stepenson,

I am in Fairfax and recommend Autobahn Serivce Center in Rockville:

301-881-1310
www.autobahnsc.com

Ask for Ned, the owner and tell him I (Eric Silver) referred you.

You will not be disappointed.

That comment about ASC being the Nordstrom dealership is accurate. They charge you higher prices for the exact same stuff you can get for less elsewhere.

Eric Silver

It sounds like the same basic set-up as my 300E. I don't know what the front of your engine looks like, so it is hard to judge the economies of replacing the pump as well. I don't know if the 350 pumps are trouble spots, so I guess I am not a great source of information.

I can recommend Silver Star Motors in Vienna, though, to do a good job at a fair price. Recently I have also had good experiences with Foreign Service in Tysons Corner.

I love ASC for their parts department - they have gone the extra mile for me more times than I can count. But I agree that their service prices are on the moon and there is no need to pay them unless you need their specialized diagnostics and it does not sound like you have a high tech problem!