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Thread: Electric fan delay, so it runs after shutoff

  1. #1
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    Electric fan delay, so it runs after shutoff

    I am installing an in-line temp sensor in the return hose to run my aftermarket puller fan. I've done the fan-delete. I'd like to wire in the relay to have un-switched power so it could run after shutoff, until the temp in the return hose drops to 165 deg. (I'm using the 180-on, 165-off switch) But, I live in Phoenix, so I'm afraid that, in the summer, the fan would run for an hour after shutoff. So... I'd like to put an adjustable time-delay to set the time it runs after shutoff to be, for example, 10 minutes. Has anyone done this, and/or know of the right delay to use? ..... as always, thanks for any responses...

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    When I was autocrossing the gray car ('01 M Rdstr) I had a timer to run the cooling fan after I'd pull back in staging. I built it from one of those electric kits and stashed it inside the fuse box (where ALL the connections I needed were already).

    I later put it to use to run the four (4) LED lights mounted to the bottom of the hood (Daniel persuaded me on that idea...). I think with dip-switches, you could set it for 4, 8, 16, 32 minutes, etc., of on time.

    Edit: Oh look, a picture...

    Last edited by Randy Forbes; 03-14-2018 at 11:58 AM.

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    If the engine is shut off, there is no circulation from the water pump so won't it just cool the hose and front of the thermostat housing while leaving hot coolant trapped in the block once the thermostat is closed? Is the main goal just to evacuate hot ambient air and get some flow around the hot block? If so I almost wonder if the polarity on the fan can be reversed, to then take the hot air from the engine bay and push it out the front bumper... maybe that is over-thinking it

    I'm also curious to see your setup once it's all finished, I am still tieing up some loose ends on my S52 and plan on installing this kind of system once its back on the road.
    Last edited by BimmerBreaker; 03-14-2018 at 12:09 PM.

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    In my case, just to remove as much heat from the engine compartment as possible, doing anything to combat heat-soak.

    Newer cars with an electric waterpump could do what you say more easily.

  5. #5
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    Quote Originally Posted by BimmerBreaker View Post
    If the engine is shut off, there is no circulation from the water pump so won't it just cool the hose and front of the thermostat housing while leaving hot coolant trapped in the block once the thermostat is closed? Is the main goal just to evacuate hot ambient air and get some flow around the hot block? If so I almost wonder if the polarity on the fan can be reversed, to then take the hot air from the engine bay and push it out the front bumper... maybe that is over-thinking it

    I'm also curious to see your setup once it's all finished, I am still tieing up some loose ends on my S52 and plan on installing this kind of system once its back on the road.
    Yes, evacuating the engine bay is the main goal. We all know the engine temp goes up after shutoff, so any help seems good. That's an interesting idea to reverse the fan. I'm not sure that would be better. It seems to me that as a "puller", it will blow more air across the engine than if it were reversed.

  6. #6
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    You could always attach heat sinks to the block, in conjunction with a fan. Kidding of course
    Tony
    2000 Estoril Blue M Roadster
    2004 BMW R1150R

  7. #7
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    Quote Originally Posted by zellamay View Post
    Yes, evacuating the engine bay is the main goal. We all know the engine temp goes up after shutoff, so any help seems good. That's an interesting idea to reverse the fan. I'm not sure that would be better. It seems to me that as a "puller", it will blow more air across the engine than if it were reversed.
    The engine block may pick up some radiant heat from the system once the engine is shut off, but the total heat in the entire system begins decreasing as soon as the engine is shut off. No combustion means no more heat is being generated The S52 is an iron block so personally I would not be too worried about it sucking up a little heat after being shut off. The BMW engines that had the electric water pumps circulating after shutoff were the aluminum block/aluminum head M54's.

    Whether the fan is pulling or pushing I think there will be airflow issues and the front of the block will receive the vast majority of the cooling. At that point I worry more about thermal stress by constantly cooling only the front of the block while the rear is still hot. Thats sort of why I was thinking reversing the fan might be good, so it is evacuating the hot air radiating from the engine, as opposed to blowing cool air on the engine (which would more directly cool it, but would mostly cool the front of the engine where the airflow reaches). I don't really think it'd be bad long-term, but I'm willing to bet that cylinder 6 will remain almost the same temperature with or without a fan running after shutoff.

  8. #8
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    Quote Originally Posted by BimmerBreaker View Post
    The engine block may pick up some radiant heat from the system once the engine is shut off, but the total heat in the entire system begins decreasing as soon as the engine is shut off. No combustion means no more heat is being generated The S52 is an iron block so personally I would not be too worried about it sucking up a little heat after being shut off. The BMW engines that had the electric water pumps circulating after shutoff were the aluminum block/aluminum head M54's.

    Whether the fan is pulling or pushing I think there will be airflow issues and the front of the block will receive the vast majority of the cooling. At that point I worry more about thermal stress by constantly cooling only the front of the block while the rear is still hot. Thats sort of why I was thinking reversing the fan might be good, so it is evacuating the hot air radiating from the engine, as opposed to blowing cool air on the engine (which would more directly cool it, but would mostly cool the front of the engine where the airflow reaches). I don't really think it'd be bad long-term, but I'm willing to bet that cylinder 6 will remain almost the same temperature with or without a fan running after shutoff.
    I hear you. Of course, I don't want to stress the block. You are right, reversing would create a more even air flow over the engine. And if you're right, that it won't make any diff anyway, I can save the hassle. I'll think about it............ Also, I'll take pics of the inline switch install.......

  9. #9
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    it would be interesting to take a thermal image with something like this:

    FLIR-ONE-Thermal-Imager

    71XBh2d6qPL._SL1000_.jpg
    Last edited by ZGator; 03-14-2018 at 07:16 PM.

    “Great wisdom is generous; petty wisdom is contentious.” 无为

  10. #10
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    You could always open the hood...

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    [QUOTE=Mr Bingley;29976090]You could always open the hood...[/QUOTE
    Or take it off completely. Decades ago I was rebuilding a 68 Mustang, had the hood off all summer. Ran cool.

  12. #12
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    I have the Zionsville radiator, with a Spal fan, and its is wired to run after shutdown until the temperature is reached. On a hot day, it sure does pull heat out from under the hood. It's a bit weird walking away from your car, and the fan kicks on, but it definitely does pull heat out after shutdown.Yes, there is no water flow during this time, but there are definitely a lot of BTU's being drawn away.

  13. #13
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    Quote Originally Posted by Mark Bielick View Post
    I have the Zionsville radiator, with a Spal fan, and its is wired to run after shutdown until the temperature is reached. On a hot day, it sure does pull heat out from under the hood. It's a bit weird walking away from your car, and the fan kicks on, but it definitely does pull heat out after shutdown.Yes, there is no water flow during this time, but there are definitely a lot of BTU's being drawn away.
    So, to help with BB's idea; after shutoff, does your fan continue to blow towards the motor, or reversed to push the air out through the radiator? Also, what is the range of the temp switch controlling the fan, and where is that switch (in the radiator or in-line)?

    - - - Updated - - -

    Quote Originally Posted by Mark Bielick View Post
    I have the Zionsville radiator, with a Spal fan, and its is wired to run after shutdown until the temperature is reached. On a hot day, it sure does pull heat out from under the hood. It's a bit weird walking away from your car, and the fan kicks on, but it definitely does pull heat out after shutdown.Yes, there is no water flow during this time, but there are definitely a lot of BTU's being drawn away.
    Good, you can be a wealth of information. So, to help with BB's idea; after shutoff, does your fan continue to blow towards the motor, or reversed to push the air out through the radiator? Also, what is the range of the temp switch controlling the fan, and where is that switch (in the radiator or in-line)? Last question: how long does it run when ambient temp is 100 degrees?

  14. #14
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    I think cooling the coolant in radiator helps in case if you have to drive soon after shutdown. I remember my stock aux fan was still working a few minutes after shutdown on hot days.

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    Quote Originally Posted by Mark Bielick View Post
    I have the Zionsville radiator, with a Spal fan, and its is wired to run after shutdown until the temperature is reached. On a hot day, it sure does pull heat out from under the hood. It's a bit weird walking away from your car, and the fan kicks on, but it definitely does pull heat out after shutdown.Yes, there is no water flow during this time, but there are definitely a lot of BTU's being drawn away.
    Is that the way I wired it, or did you/someone else alter it?

    I don't remember, slept since then...

  16. #16
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    The fan runs normal direction. All it does is pull heat out of the radiator, which eventually lowers the under hood temperatures. The temperature switch I use is the 80/88 DegC. It is in the radiator. It runs as long as 5 minutes after the car is shut off on a hot day.

  17. #17
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    Randy, I added the Spal after you did the radiator install. My aux fan connector failed in traffic on a hot day, and I almost overheated the car. After that, I wasn't going to take any more chances. I went back to Dwight at Zionsville, and he helped me get the Spal system added. Haven't had a problem since.

  18. #18
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    Quote Originally Posted by Mark Bielick View Post
    My aux fan connector failed in traffic on a hot day, and I almost overheated the car.
    Somehow recently I read a lot about aux fan failures, despite someone on this forum saying it's very reliable.

  19. #19
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    My fan did not fail. The wiring connector at the fan input failed. It is a snap fit connector, and somehow it had worked itself loose to the point where the electrical connection was lost. I have since fixed the connector, so all should be OK. Still, fans, like anything else, can fail over time.

  20. #20
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    Quote Originally Posted by Mark Bielick View Post
    Randy, I added the Spal after you did the radiator install. My aux fan connector failed in traffic on a hot day, and I almost overheated the car. After that, I wasn't going to take any more chances. I went back to Dwight at Zionsville, and he helped me get the Spal system added. Haven't had a problem since.
    Thanks for clarifying that, as I didn't recall ever wiring one to stay on after the engine had shut off.

    One of the weirdest installs I did was wiring in a Turbo-Timer; it let the engine continue to run for a predetermined amount of time after you took the key out, locked the doors and walked away.


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    Quote Originally Posted by Randy Forbes View Post
    Thanks for clarifying that, as I didn't recall ever wiring one to stay on after the engine had shut off.

    One of the weirdest installs I did was wiring in a Turbo-Timer; it let the engine continue to run for a predetermined amount of time after you took the key out, locked the doors and walked away.



    I'm surprised to hear you say "weird". .......... I installed a turbo-timer on my 3000ZX TT. We all know one should not shut off the engine just after running at any speed because the turbos will spin for a long time without oil feed. Before the turbo-timer, one would sit with the engine idling for a while before shutting off. There are alternatives, but the turbo timer is easy. So I am not an expert, but they make sense to me for a turbo car.

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    Quote Originally Posted by zellamay View Post
    I'm surprised to hear you say "weird". .......... I installed a turbo-timer on my 3000ZX TT. We all know one should not shut off the engine just after running at any speed because the turbos will spin for a long time without oil feed. Before the turbo-timer, one would sit with the engine idling for a while before shutting off. There are alternatives, but the turbo timer is easy. So I am not an expert, but they make sense to me for a turbo car.
    Redirect Your Honor...

    Not weird for the application, but for the act of walking away from your parked car after switching it off.

    I rest my case.

  23. #23
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    Quote Originally Posted by Randy Forbes View Post
    Redirect Your Honor...

    Not weird for the application, but for the act of walking away from your parked car after switching it off.

    I rest my case.
    Whew. I thought I might learn that another long-held belief of mine was all wrong...............

  24. #24
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    I've also had a failed aux connector. It worked its way loose and the electric arcs melted the ends together. Had to replace it. Body shop insisted on replacing it for me and ruined a perfectly good Deutsch connector set.

  25. #25
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    I finally installed the inline temp switch to run only the aftermarket puller fan yesterday (before I figured out I have a rod knock, separate thread). It was easy to install and works as expected. The fan came on after stopping for a minute or two, and turned off almost immediately after moving again. It's a 180/165 switch. It is wired un-switched, so it can run with engine off. (So far, regarding the possible block stress discussed above, I think heat transfer would be too slow for that to happen.) After shutoff, it ran about 90 seconds, about right for 75 deg ambient temp. The aux fan, still wired stock with the 81 deg switch in the radiator, never came on. ...... So, I would recommend this mod to anyone with a fan delete and 2 fans. ... For your convenience, here's where I got the parts: https://www.amazon.com/Upgr8-Aluminu.../dp/B00FY2LWII & https://www.amazon.com/dp/B079633F11...ing=UTF8&psc=1
    Last edited by zellamay; 03-19-2018 at 08:51 PM. Reason: add parts refs

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