I just purchased an 85 MB 300D turbo and when I drive it at approx. 35 mph it makes a squeeling noise and again at approx. 55 mph. I read a posting that said to put wd-30 (wd-40) on the belts to see if it goes away, it didn't. There is no noise when the car is idling or when it is reeved in park or neutral. It is not the A/C compressor either because it does not work and it is turned off. I wish i had found this forum 3 days earlier and i would have found the posting on what to check for when buying a used diesel (very helpful but too late for me). I am a newby on diesels any advice will be greatly appreciated.

 

Is this happening when you are driving on a smooth road or is it when you are going over bumps or turning? It's common for these cars to have bad ball joints and/or support rods plus a lot of the bushings get worn out. Remember you just bought a 23 year old car and any car has part that need to be replaced especially as they get older. If this is suspension related and you are willing to do the work most of this stuff can be a DIY project.

 

An additional comment. Make sure the belts are properly adjusted and all fluids are up. Belts that seem tight can be just loose enough to make noise and low fluids might cause more drag on things like the power steering pump. Check the belts to see if they are glazed because that can cause noise also.

 

Thank you for your reply. It does not matter if i am turning or on the highway the noise starts up at approx 35mph and last until 40 and then again at 55 to 60. if I drive steady at 45 or 25 there is no noise. I checked the belts they are ok and not loose. All of the fluids are topped off except for the trans fluid I can't find the location of the dipstick.

 

trans dipstick should be on passenger side near firewall with a red top

 

Try touching the brakes with your left foot maintain speed with your right and see if the squeel stops. Does it do it if it is wet, pressure wash around your suspension parts. WD-40 will make your belt slip liqued dish soap is a good belt dressing when it dry's. Also could be your altenator, but rule out one thing at a time.

 

An auto store will sell you the proper "belt dressing" which is the same as for electric motors. I have used it on fan belts in the past. It removes the glaze. Any type of oil or detergent can cause belt slippage is applied too liberally. It is slippage that causes the squeal.

 

replace belts with new belts, goodyear gator grip belts are exellent, not a lot of stretch.
if using economy belts, a/c compressor belt will have to be retightened within days because
of stretch.

 

I too have same experience with my 1985 300td wagon recently. One mechanic told me it was the turbo another says he is positive it is the trap oxidizer ( a crack in it.)( check to see if it has been replaced , mercedes will do it for free "one time only" because it was a recall part (only the 85's) for calif. state emission control ) Your mention of the mph and noise are the exact same as mine. I personally don't believe either as my car was not making this noise before I took it to have work done by a new mechanic . He charged a fortune and when I got my car back it made this noise. The websites have mentioned a screaching sound is the turbo. Find a true deisel mechanic if you can. Good luck, let us know how it turns out.

 

OE Conti v-belts are best for this car.