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Thread: Custom electric fan install

  1. 20th October 2020, 04:29 PM #1
    Finnius's Avatar
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    Custom electric fan install

    Hey folks,
    I have installed a 20A electric fan on my 300Tdi.
    I have a 88 degree fan thermostat switch threaded into one of the bungs at the thermostat housing of my 300Tdi.
    There is a fused ignition feed running to one side of this thermostat which when the switch is closed triggers a 30A relay which has fused power supply to the electric fan.

    My problem is a strange fluttering electric motor sound when the engine coolant is at the cut off temperature.
    Everything works beautifully when the engine is working hard but when the engine is running cool, the thermostat fan switch seems to be opening and closing rapidly when the engine coolant is around 88 degrees.
    This fluttering of the thermostat is rapidly turning my relay on and off and subsequently looks like it has burnt the contacts inside the relay. Now the fan cant pull enough amps through the relay to fire up.

    I was under the impression that the thermostat I bought was meant to kick in at 88 and not turn off until 75ish (approx) - the whole point of which is to avoid an oscillation like this! So I am unsure if I have diagnosed what is happening incorrectly or maybe the fan thermostat switch is faulty...

    Any thoughts?
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  2. 20th October 2020, 04:37 PM #2
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    scarry
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    You could be getting low voltage at the relay coil,check with a meter.
    This could be caused by a faulty thermostat.

    Or the thermostat differential is to close.

    Both issues will cause the relay chattering,as long as it’s also wired up correctly.
    Check wiring to make sure load is not going through thermostat,as it may not be rated for those sorts of currents.
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  3. 20th October 2020, 04:54 PM #3
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    Quote Originally Posted by scarry View Post
    You could be getting low voltage at the relay coil,check with a meter.
    This could be caused by a faulty thermostat.

    Or the thermostat differential is to close.

    Both issues will cause the relay chattering,as long as it’s also wired up correctly.
    Check wiring to make sure load is not going through thermostat,as it may not be rated for those sorts of currents.
    Thanks, the fan get's it's power through a 30A fused cable running to the relay. The ignition trigger feed is 10a fused so as it is a 20A fan it would have popped the fuse it if it was pulling through the ignition feed.
    I will double check the trigger voltage making it to the realy again - but I am pretty sure I checked the ins and outs and all were above 12V.

    By 'thermostat differential', I presume you mean the range between the cut in and cut out temperature? Which was meant to be about 10 degrees... It's looking like a faulty thermostat switch - which sucks as I bought it new.
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  4. 21st October 2020, 09:53 AM #4
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    can't you set the differential your self?

    I thought that was always the case with thermo-electric fans.
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  5. 21st October 2020, 10:49 AM #5
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    Quote Originally Posted by ramblingboy42 View Post
    can't you set the differential your self?

    I thought that was always the case with thermo-electric fans.
    Nah, I installed a super simple setup that is basically a threaded thermo fan switch that is the exact thread of the holes on the thermostat housing. The switch is brand new but the part number gets used in an Alfa Romeo apparently.
    Pretty flash for a Landy!

    The fan is a badass Revotec/Comex 20A puller fan from the UK. With a custom 3mm steel shroud I cut out with the plasma cutter. When it works, it works REALLY well. I have a full width front mount intercooler and the fan pulls a lot of air straight through the intercooler as well as the radiator.

    The differential is meant to be something like 10degrees, which is why I chose that thermostat...
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  6. 30th October 2020, 03:06 PM #6
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    88.C is right on the cusp of the thermostat, so the temp will always fluctuate in that range. Perhaps a switch that operates above that range (ON @ 95.C - OFF @ 90.C) might work better.

    Also if you run fused 12V to the relay for power and for switching you can get away with just one wire and one fuse, with a loop to connect the two terminals. Then use the thermostat switch to run earth on the low amp switch circuit of the relay.
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