Viscous fan problem.

[jam172]

Can anyone explain to me in simple terms how these work?

My I.S. engine is getting very hot in traffic, i have done the rolled up newspaper test and even when the engine is hot, i.e. 3/4 of the way up the gauge, i can still stop the fan easily. I have tried 3 other 2nd hand one's and they are all the same

help please.

[Ziggy]

Basically, there's some stuff inside them that solidifies & locks the coupling when it gets hot, so that the fan gets driven. If you can stop the fan when it's hot, then the coupling's not locked & the fan's not doing its job.

[jam172]

That's what i thought, but i have tried 2 other 2nd hand one's, this must be a very common fault for both those to be knackered as well?

[Ziggy]

Yup... Also storing them flat (rather than oriented as they would be on a car) supposedly ruins them, & I reckon a lot of second hand ones have suffered from that.

[jam172]

Thanks Ziggy, looks like a new one is needed then.