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Thread: Radiator fan not going on

  1. #1
    Join Date
    Apr 2013
    Posts
    143

    Default Radiator fan not going on

    I did a track day last week - SCCA Track Night in America, at Thompson Speedway (CT). In the Intermediate group I generally was faster than the BMWs, Miatas, lesser Porches, etc., and kept up with some of the 911 Turbos and Corvettes. My car was a bit hit with lots of the folks there. Very fun.

    Only problem was that my engine ran pretty hot, and when I came in after sessions it boiled over when I was running it to cool down. Driving home it ran pretty hot, and I figured out that my radiator fan wasn't going on. That's why it was fine at speed on the track, but boiled over when idling. My engine is a BDA, but I assume this would all be the same on a crossflow.

    I checked the fan fuse - looks fine.

    Basic questions:

    In this picture, there is one sensor on the left, with a black and a yellow wire, and one sensor on the right, with a green wire:



    I assume the one on the left controls the radiator fan, and the one on the right is for my coolant temperature gauge. Correct?

    This picture shows the wiring going to the fan:



    Black and black/green coming from the wiring harness, which is what my wiring diagram shows. These go through a connector to black (grey?) and blue to the fan.

    I assume that black is ground, and black/green should deliver +voltage when the engine heats up. Correct?

    So I can check for no voltage when cold, and voltage when hot.

    Is there a relay somewhere that could be bad?

    Any other advice on what/how to check? I'm sure some of you have been through this before.
    1997 Caterham, BDA
    1991 Miata, supercharged
    2017 VW GTI

  2. #2
    Join Date
    Nov 2010
    Location
    New Jersey
    Posts
    233

    Default

    You are correct with the identification. I had the sender fail so that’s a good place to start by bypassing and see if the fan activates irrespective of whether engine is running or not. Yes there should be a relay. Also if the coolant level went too low, it may not reach the sender so the fan won’t come on. If you don’t have a manual bypass switch for the fan maybe consider adding one for peace of mind.
    1985 Caterham Super Seven
    1952 MG TD
    1991 Lotus Elan
    2017 MX5 RF
    2018 Audi A5 Sportback
    2014 BMW X1

  3. #3
    Join Date
    Apr 2013
    Posts
    143

    Default

    So - If I connect the black wire and the yellow wire attached to the fan switch the fan should go on - right?

    Great idea re wiring a fan switch - thanks. I could use the switch for the heated windscreen, as I don't use that and never would.

    Quote Originally Posted by The Stig View Post
    You are correct with the identification. I had the sender fail so that’s a good place to start by bypassing and see if the fan activates irrespective of whether engine is running or not. Yes there should be a relay. Also if the coolant level went too low, it may not reach the sender so the fan won’t come on. If you don’t have a manual bypass switch for the fan maybe consider adding one for peace of mind.
    1997 Caterham, BDA
    1991 Miata, supercharged
    2017 VW GTI

  4. #4
    Join Date
    Sep 2020
    Location
    Kelowna BC
    Posts
    7

    Default

    I’m curious how this turned out?

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