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Fan cut-off


kevindawes
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Apologies as this this isn't really a megasquirt question.

I've just fitted an electric fan to my 3.9 defender (engine came from a disco) and I was wondering what temperature most of you have set for the fan to kick in?. Currenty I have mine coming on a 87c and then switching off a relative 10c lower which isn't adjustable.

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The standard v8 thermostat is set for 82c so no point having it lower, they usually recommend to be at least 5C about thermostat temp.
The data on the Viscus fan suggest that it's control range is 85 to 100 deg C

I run the standard X-eng switch which is 88 degrees C and off at 83 and then 92 and off at 87 for second fan

I think that a cutoff of 77C would be too low as is would cause the thermostat to start to close before the fan goes off.
Not sure why you have such a large range.

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RAVE manual describes stat operation, an 88deg stat isn't even fully open till somewhere around 92deg+ so no need for the fan to kick in until after that. There's a lot of over-cooling goes on based on what people did in the old days.

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Indeed... No point having the fan cut off below thermostat temp!

Think I have mine, with an 82C stat, set at 85 on 83 off, works fine, cycles fairly quickly at that (so could put the upper temp up a touch I think?), but that's OK with me, running twin mondeo fans in an RRC though :)

74C is really cold for a road-use engine, you will likely get condensation build up and milky oil, only really suitable for full-race applications IMO, where oil is changed every event.

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If you cut in too soon the fan & stat will get into a loop and be constantly on/off in/out thermal cycling the block which isn't great for it. A mate has a theory that electric fans kill TDI's this way as the head & block are dissimilar metals & expand/contract at different rates.

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There's a lot of over-cooling goes on based on what people did in the old days.

Figures quoted above certainly seem low, but I wondered what 'the old days' approach may refer to?

Just cooling as much as possible was 'old tech' I guess?

Do you agree or disagree with what Ramon describes about [sD1] RV8 cooling issues here?

http://www.vintagemodelairplane.com/pages/Snippets/EngineTemp01.html

He has a lot more theory (and fact) here, which can make for interesting reading.

http://www.vintagemodelairplane.com/pages/Downloads/Rover_PDFs/RV8EfiCooling01.pdf

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  • 1 month later...

I've set mine to come on at 92deg (measured by MS and about 97 on my dash gauge) and it automatically turns off around 85deg. Green laning last week in france it seemed about right as when the car was running away from the wind the temp rose quickly and the fan caught it and brought it down reliably. When I drive off-road in spain the ambient temperature is much higher so when driving up long slow rocky hill and gravel riverbeds (engine working hard) I think I'll have a bit of a safety margin.

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