Viscous Coupling

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tonyc280

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Joined
May 22, 2010
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Location
Leicestershire
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1997 C280 V6 Elegance Auto Facelift. 1992 Kawasaki ZZR1100 C3
I understand that a "Viscous Coupling" works on the principal that when the oil inside gets thicker it spins quicker but surely that's not the case as fluids get thinner when hotter. Forgive my ignorance if in missing something. T.:doh::dk:
 
I think the fluid in a viscous fan actually thickens as it gets warmer. Some kind of silicon I think .
 
I never knew how complex the "Viscous Fan" was and what an important part it plays. Thanks chappies. Would be good if everyone read the topics highlighted by Grober. Little things please little minds ha. Well it pleased mine anyway. T.
 
Dear all my viscous coupling has been under my workbench for three years now. Without the fan the engine is quieter and no doubt uses less fuel. However I do rely on the electric fans but they have only been on three times and the coolant temperature rarely exceeds 100C. Frankly in my opinion, in the UK an E 300 does not need the belt driven fan. (for heavy towing it might be advisable). The electric coolant pump is i am sure very important for a very hot and stopped engine. I reguarly listen out for mine.
 
The electrical fan/s are normally only fitted to cars with airconditioning as a supplement to the viscous coupled engine fan. You must remember these systems are designed to be used in far hotter climates than the UK. As it is you may well get by with the electric fan/s in the temperate climate of the UK. I think it would mean the engine would be running a few degrees hotter before the electric fans cut in compared to a correctly calibrated viscous fan.
 
I remember a post by Dieselman telling us that he had removed the belt-driven fan from his E300TD.
He assured us that the engine would NOT overheat.
I've never quite had the courage to do this to mine.
 
I have been in London in summer heat in traffic with no viscous fan, the electric fans come on at around 103 deg C but only for a few seconds probably once a year. Mine is ready to go back in service. A great advantage is better access at the front of the engine and it really is so much quieter. I am sure it is well over cooled compared to most other vehicles. I agree with Grobers comment that best not to remove it unless you have electric fans as back up.
 
Careful with keeping the viscous coupling on the work bench - if it's face-down, the fluid will move into the wrong compartment and the coupling may never work properly again. Apparently that's why the boxed originals should always be stored vertically, so the coupling is kept the same way up as it is when mounted on the engine!
But I think you're probably right, the cooling on a lot of the older MB engines is impressively over-specced!
 
Dear all my viscous coupling has been under my workbench for three years now.

I'll raise you three.

I remember a post by Dieselman telling us that he had removed the belt-driven fan from his E300TD.
He assured us that the engine would NOT overheat.
I've never quite had the courage to do this to mine.

Never got near 100C yet. The hottest I have seen is about 97c, but even when stuck in a motorway jam after a decent drive it never goes past 95c or less normally.

Normal cruising temp is ~80c, just as it always was, but the engine definitely warms up more quickly from cold, especially in Winter.
 
On my W202, the viscous coupling went - I ignored it for a few days, then found myself stuck in traffic (in east London) in summer.

My radiator sump (plastic bit on top) exploded with a very loud bang. Steam came out of the air vents inside the car, and generally felt like a small bomb went off in the engine bay.

On the W202 C180; I can assure you the viscous coupling pays a very important role ;)

M.
 
I wouldn't remove the fan on any petrol engined car, they just waste too much energy as heat.

The "header" tank (sumps are at the bottom) on your car was just a weak part, the cap should vent off excess pressure.
 
I wouldn't remove the fan on any petrol engined car, they just waste too much energy as heat.

The "header" tank (sumps are at the bottom) on your car was just a weak part, the cap should vent off excess pressure.

Should... unless weeks of slow venting/evaporating has caused the little pin/spring assembly to fill with dry gunk and seize up ;)

Quite spectacular tbh - was my first car in the UK and had 3 ladies in the car (ah, the joys of university....)

M.
 
Ah ---viscous coupling with 3 girls in a car--- those were the days! ;)
 
funny how a thread can start over again after four months.
 

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