124 Making a Bad Noise
 

On my way to work this morning, my '87 300D started making a terrible noise. At first I didn't notice it, but then I accelerated rather hard, it made the noise, then I started listening very carefully. The noise only seems to get loud when the turbo really kicks in. It sounds like something is grinding. If the car is running under normal acceleration, the sound is almost unheard. I did discover that the noise got louder when I turned on the AC. I don't know if this was due to a heavier load on the engine. I doubt if it is the turbo as it was replaced not even a year ago. The noise appears to be coming from the very front of the engine. I removed the oil cap and took a peek in there with a flashlight and didn't see anything obvious. The car is running fine, no rough idling, plenty of power, etc. I am alarmed at the racket it is making though. Any ideas as to what this noise could be would be appreciated.

This may sound stupid, but is it the belt? The ugliest sound my car has ever made was when the belt slipped. Had me wondering "who's out chainsawing?" before I realized it was my car ...

I looked at every part I could lay eyes on under the hood and couldn't see anything obvious. The belt is riding on all of the pulleys properly. What does it sound like when your water pump or vacuum pump are about to give out? These are two parts I have not replaced...yet.

Go to McParts and buy an automotive stethoscope for 10 bucks.
With the engine running carefully touch the metal probe to each accessory
driven by the serpentine belt. Do it with the A/C on and off.

You should be able to isolate the noise.

Steve

Will do. I am hoping it is something easy and inexpensive...I am getting really tired of working on this one. I have plenty of general maintenance to do on the wife's but haven't had time to do it since I have been devoting all of my time to the '87.

The biggest "trickster" on these OM603 engines, I have found, is a worn belt tensioner!

I heard ticks, and knocks, that had me looking and listening, with a stethoscope, and found the bearings within the worn belt tensioner were responding!

Could be something else, but I'm a mechanic, and it fooled me..........!

Give it a look?

I can't see where it would be the belt tensioner. The noise gets louder as the RMS raise to the point where if you really get on it, it sounds like something is going to give way. What are the symptoms of a oil pump going bad on one of these gems? The more I listen to the noise, the more it appears it is coming from the lower part of the engine. The oil pressure is right where it should be, and the car is not running hot. I am really at a loss here since the car is running great other than the rather loud noise it is making.

I'd check the A/C compressor or alternator since they're both down there.

I received my parts from Fastlane on Tuesday...was surprised how fast they arrived with Ground Shipping (two days). I took the day off work yesterday and replaced the water pump which was the part I suspected to be bad. Once I removed it, I did discover how noisy it was when spun by hand. The other alarming problem I discovered was my main crank pulley...the main bolt was backed off quite a bit and you could turn the bolt by hand. How in the world did that come loose? I tightened everything down, put it all back together, took it for a test drive, and my belt tensioner pulley gave way causing my belt to break... I am waiting for the dealership to open so I can see if they have my parts on hand. I had a really hard time getting the belt back on yesterday so I am wondering if I did something worng, or if the pulley decided it was time to give way. It seems that there is only one way that belt could possibly go on so I can't imagine I did something improper.

Bottom line, the dreadful noise I was hearing has been located, and fixed. Now I am on to my next project.

Mike