Strange noise front of engine bay 300d OM617
 

This morning when I fired up the '85 300d I immediately got some weird sounds from under the hood.

Not mechanical, more like a snapping sound like electrical arcing. Heard it about five times maybe a second apart at first.

By the time I got out and got the hood open it was less frequent, decreased quickly in frequency and stopped while the car was sitting. I heard it faintly once or twice while backing out of the driveway. Didn't hear it once I was on the road.

As best I could tell, it was coming from the front of the engine bay, the areas of the vac pump, water pump, pulleys.

Can a failing vacuum pump or water pump make such a weird sound??

The belts are in top shape and the fan isn't touching the shroud (first thing I looked for). AC was off.

Tks

Check around the battery wires ,with that much popping its gotta a be a main wire hitting something metal.

Yes I suppose that and the alternator would make sense.

It can be hard to pinpoint a noise over a running diesel, but I could have sworn it was coming from the driver's side.

As stupid as it may sound, with the hood closed it sounded clearly like it was coming from behind the driver's headlight (which makes no sense as it's just empty space).

If it's electrical it'll probably happen whether the engine's running or not. Try doing a 'wiggle test' on the wiring.

Another option is to wait until it's dark out and watch the engine run -- any arcing should be pretty easy to spot then.

I must have been half asleep when I listened to the noise Friday. It doesn't sound like arcing.

Today I started the car from cold with the hood open and a neighbor listening with me.

It's an intermittent scraping sound, he says it sounds like loose ball bearings. It is coming from the area of the clutch fan and water pump.

I checked the clutch fan and it stops turning immediately on shutdown, so I guess it's shot. I had noticed over the last few days that my temp gauge was a touch higher than usual.

Questions: will a seized up fan clutch make such noises when cold?

Or is it more likely the water pump, and the clutch fan is just a coincidental failure?

It is only occurring on morning startup. Rest of the day it isn't there as far as I can tell.

Remove belts to isolate the sound.

Sixto
87 300D