Mercedes 410D OM602 viscous fan problem - fan on all the time after new fitting.

[funkyronster]

My 1993 410D was overheating on long hills, and I could no longer hear the fan cutting in.

After having a new viscous fan coupling fitted, my fan is now on all the time and noisy as hell, and the engine is running super cool, even on the same long hill. The fan noise is like a jet engine and louder than the engine - it's driving me nuts.

I took it back to the garage and they fitted another brand new unit - sourced from Mercedes - same result. The garage says no fault - they are all like that.

I disagree - I have had this 410D for 20 years and it has never sounded like this.

My question is - is it possible to wrongly fit a new coupling in such a way as to cause the fan to be permanently engaged? Perhaps by over tightening?

My online research indicates that it should be tightened to 32 ft lb - I didn't see the mechanic use a torque wrench and I am wondering if he over tightened it.

It is too much of a coincidence for 2 brand new visco couplings to be faulty.

Many thanks

 

[Doug1234]

If it’s like a jet engine when you start up on a cold engine then it’s faulty.
If it isn’t I would be getting a cheap digital hand held temperature gun circa £15 off eBay and checking all the frontal area of the radiator.
I have read countless posts over the years ( on the Peach parts diesel discussion forum ) of overheating troubles on the 410D’s and others in the models range and it’s always been 60% radiator has cold spots where it’s getting blocked up.

 

[funkyronster]

If it’s like a jet engine when you start up on a cold engine then it’s faulty.
If it isn’t I would be getting a cheap digital hand held temperature gun circa £15 off eBay and checking all the frontal area of the radiator.
I have read countless posts over the years ( on the Peach parts diesel discussion forum ) of overheating troubles on the 410D’s and others in the models range and it’s always been 60% radiator has cold spots where it’s getting blocked up.

Thanks, the radiator was replaced a couple of years ago. Do you know if over tightening could cause 2 brand new visco couplings to fail? As in fail fully engaged. The fan is on all the time - it's obvious from the noise and from the temp gauge being much lower than normal.

 

[Doug1234]

I do not think over tightening them can cause them to jam.