C180 Whine

[joneseythedog]

Dear All

I have a 1995 C180 Auto. I have recently noticed a dull whine coming from the engine area (as far as I can tell when driving), at engine speeds of around 2500 - 3000RPM. Can't hear it at higher speeds, but that doesn't mean it is not still there.

It doesn't seem to matter which gear I am in, so I don't think it is the diff.

It seems to get a little quieter when taking my foot off the accelerator.

I've tried revving the engine while stationary, but the engine seems much louder then and I have been unable to hear anything much.

Have thought of listening to various parts using a screwdriver or other similar stick between my teeth when it is running (but not when driving!), but am worried about the proximity to moving belts etc.

Any suggestions as to how to narrow it down would be appreciated - I don't want to look like a neurotic owner at the local MB dealer, as my wife can't hear anything, and I am now wondering if I am imagining things

Thanks,

Andrew

 

[C220GJS]

Check whether your engine fan coupling is able to freewheel when cold, as if it locks up it will run at full speed constantly and cause a roaring noise at anything over tickover.
If it has locked up it needs to be replaced as the fan is not designed to run at such high speeds.

 

[joneseythedog]

That sounds interesting. Do I check this by attempting to stop the fan with something when the engine is running? 'The carrot test' rings a bell - if it gets sliced there's a problem, if it stops the fan all is ok, if I remember correctly.

Andrew

 

[C220GJS]

You should be able to turn the fan by hand when the engine is cold with only a slight resistance to turning,if it is locked as I said it is faulty.
On the other hand if you can stop the fan when the engine is hot (the carrot test)it is also faulty.
In either case it is the viscous coupling which needs to be replaced not the fan itself

 

[joneseythedog]

Carrot test passed!

Took car to MB dealer nr. Hull today. Looks like the alternator is on the way out.

Any recommendations as to good parts suppliers?

Andrew