Noisy Viscous Coupling?

[Neil Thompson]

I've just given my 280 a good, long, fairly hard run to clear the cobwebs out prior to some long overdue UK Autumn/Winter weather arriving forcing it to be tucked up in my garage!.

The question I have, no doubt asked before, is that when the engine was hot there was a metallic noise coming from the bonnet (hood in the US!) area. It sounded like, say, a loose exhaust heatshield or a pipe or cable resonating against the body etc. I found nothing loose except that there is some play in the cooling fan viscous coupling. Holding the fan blades and moving them forward and backwards I can not only feel the play I can also see it!, another sympton is that when I accelerate fairly hard from standstill I momentarily get a high pitched scream like a loose alternator belt under load.

Dear knowledgable members, am I assuming correct? and if so is the part still available from Merc or are there other suppliers recommended (UK pref) or have any members got a good one for sale?

Thanks in advance

Neil

[Larry & Norma]

When I had a noise like that it turned out to be a loose power steering pump.
It was held in place by the belt as the rear bolt and spacer were missing!

[Neil Thompson]

Thanks Gnuface but the play is forward of the pump and the pump isn't falling off! but would like to hear from members if the viscous coupllng would produce the noises as described.

[DaveB]

I checked the viscous clutch on my 250S parts car and it also has visible, and audible, play. However the car has never run since I've had it so I can't confirm whether it's functional. Can you run the car awhile without the belt to see what happens? I don't know whether there are any serious risks doing that. I've done it before with no apparent ill effects, on other cars though.
Replacements are available. The genuine Behr from MB will be expensive but I think there's a cheaper option from the other suppliers listed on this site.

[hands_aus]

Dave,

John Green in Canberra could be able to supply the Behr without the Star logo.

http://www.mbspares.com.au/

[tel76]

Hello Neil,
If i had that problem i would remove the viscous/fan and run it ,if you moniter the temp: gauge you will be ok ,i personally do not think that is your problem,when i got this project i drove the car about 20 miles,there was no strange noises,when i removed the fan assy: as part of the strip down i found that the viscous unit had excess (dangerously) free play and was leaking its fluid.
Name corrected

[DaveB]

Not really a problem for me, I don't intend to do anything with the 250S, I was just checking the fan clutch to see if it shared the symptoms Neil described. If you say yours was silent despite being worn out then you're probably right that is not the problem with Neil's car.

[Neil Thompson]

Thanks all, if we get another decent day I'll isolate the coupling and run it up until warm and then re assess

Neil