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Thread: Thermo switch for cooling fan

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  1. #1 Thermo switch for cooling fan 
    frequent forum contributor Club Member element's Avatar
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    Ever since I have had this Marlin, every time I have driven it more than 1/2 a mile, the fan has switched on when I turn the engine off. Not such a bad thing and it certainly attracts attention when the fan is whirring away. There was probably a central top dial knob to adjust the thermo switch setting but it's long gone now. I just lived with it.
    However, a few weeks ago, on a sunny day I thought I'd go for a drive and when I turned the key there was nothing, no battery power whatsoever. Eventually I traced the problem to the fan switching on when I put it away in the garage & closed the door - but it had stayed on and flattened the battery. Since then this extended fan running time seems to have become more and more of a problem - so much so that I am now forced to unplug one of the wire leads at the back of the switch to manually disconnect it. Problem then is - I have to remember to reconnect the wire as otherwise the engine can overheat when going up big hills around here on hot days - unless I happen to see the water temp gauge!

    So basically I'm looking for a means of fixing the problem - or modifying the current thermo switch to switch on at a fixed temperature and switch off after either an adequately cooler one or else after a maximum time of maybe 10 minutes..

    What have you used / done to achieve a balanced system? This one looks to be set off by the fine copper pipe with an expanding tip that switches the electrical contact to on.. but it really needs replacing.
    2002 Marina based LWB Roadster with Fiat 2.0 TC engine & box
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  2. #2 Re: Thermo switch for cooling fan 
    frequent forum contributor Club Member element's Avatar
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    https://rimmerbros.com/Item--i-KLM1416

    This looks very similar to mine.
    2002 Marina based LWB Roadster with Fiat 2.0 TC engine & box
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  3. #3 Re: Thermo switch for cooling fan 
    Club Member dcunn's Avatar
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    Might be worth a while with mole grip onto the "knob" and see if turning it into different positions has any different results?

    If the switch is working, shame to replace it, sourcing a knob should not be a problem
    Last edited by dcunn; 29-05-2019 at 06:44 PM.
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  4. #4 Re: Thermo switch for cooling fan 
    regular forum contributor Club Member nigel_cordrey's Avatar
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    why can't you just rewire the switch to a ignition switch live. I've drilled and tapped a hole in the thermostat housing and fitted a radiator fan switch cambiare part number VE709047
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  5. #5 Re: Thermo switch for cooling fan 
    frequent forum contributor Club Member
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    I used to have that setup but when the switch gave up I replaced it with this in the top hose. Been fine since. Switch was 95/85 one.
    Usually if the fan's running when I stop, which isn't very often, I let it tick over for a min. or two before shutting down.
    I also fitted an over ride switch so that when in traffic on a hot day I can cut it in. Also helps to keep the temp. under the bonnet down.

    https://www.ebay.co.uk/itm/Stoney-Ra...tvdGmZ7G4jozFQ
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  6. #6 Re: Thermo switch for cooling fan 
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    Thanks Hugh, that link will be helpful for me too as I am at that stage with the radiator.
    1275 Marina/Ital based LWB Roadster in the process of a ground up rebuild.
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  7. #7 Re: Thermo switch for cooling fan 
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    Quote Originally Posted by h_m_cumming View Post
    I used to have that setup but when the switch gave up I replaced it with this in the top hose. Been fine since. Switch was 95/85 one.
    Usually if the fan's running when I stop, which isn't very often, I let it tick over for a min. or two before shutting down.
    I also fitted an over ride switch so that when in traffic on a hot day I can cut it in. Also helps to keep the temp. under the bonnet down.

    https://www.ebay.co.uk/itm/Stoney-Ra...tvdGmZ7G4jozFQ
    Car builder solutions have a similar in hose adapter which I used. The adjustable switches are too tempting to fiddle with all the time!

    Wire the fan through a relay with the earth going through the thermo switch. You can add a manual switch in an additional earth, so if either switch provides an earth then the fan will run.
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