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Testing a viscous fan

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I'm sure this has been covered before but i cant find it anywhere!

How can i test if my viscous fan on my 200tdi defender is working? I get an increase in temp above the normal position of the gauge when i am stuck in traffic and climbing inclines on the motorway. The temp rises more in traffic than when moving on the motorway, but i still notice it in the latter situation.

When the engine is hot (and off) after a good long run the fan spins freely, no resistance at all - does this sound like a fan that has failed or am i assessing it incorrectly?

I'm not really bothered about fitting a leccy fan and have read all the threads on that, so no need to go over that again! I will replace the viscous unit if it is shot.

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No hurry because the ambient temperature won't be high enough to bother you for the 8 months.

Definately! Even this summer in the hottest weather, the engine only got hotter on a couple of occassions, never into the red on the standard gauge, but it was enough for me to notice as it was toward the far right of the white section. Had to turn the heater on full to try and get rid of some of the heat - the cab got very hot!

Have a viscous unit on my old TD engine that i might try on it first (i think they are compatible?). I'm pretty sure that was working when that engine was removed.

I also keep meaning to get a gauge that reads in C so i can be more accurate with problems like this!

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I suppose the best indication that it's working is if you can hear it "roaring" when you rev the engine after being stationary for a long time with the engine ticking over (usually once the temp gauge starts to rise.)

The other way is to stick your hand in there and see how many fingers it takes off before stopping. :blink:

My Td5 used to do this quite regularly when stuck in traffic jams. When on the move though, there is usually enough airflow over the coupling to prevent this.

Even if it doesn't get to the fully locked up (roaring) stage, there's usually enough coupling across the viscous unit to provide a fair degree of cooling. If you're not getting it actually overheating, I wouldn't worry too much.

I've had one seize up altogether once, but then you get the roaring all the time so its pretty obvious then.

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