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Thread: Cooling fans question Diablo Roadster!Need Help!!

  1. #1
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    Cooling fans question Diablo Roadster!Need Help!!

    This morning i noticed the fog light wire and electric choke wire were disconnected from the fuse box(normally they are plugged in directly into the fuse box) I plugged them back in in two empthy spots and drove off. Drove the car for about 5 minutes, made a quick stop of about 10 minutes and drove it back home about 5 minutes. Never had overheating issues before so before I realized the temp gauge was at 250. Shut the engine off and noticed foul smell as some coolant leaking. After quick inspection I realized the rear radiator fans didn't work. They are otherwise connected with a thermostat dial on the coolant hose and automatically kick in when the car reaches 180. But for some reason they didn't turn on. What would cause the cooling fans to stop working? I checked the fuses(I thought maybe I plugged the fog lighs and chocke wires wrong and cause a short somewhere but all fuses checked out fine).
    I restarted the car again when it cooled down to 180 and put some coolant in it but it was idling little different. What would I should look for and what are the chances of me damaging the motor. This motor has high performance internals and its not a stock GM 350.
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    Last edited by redhammer; 07-22-2013 at 06:49 PM.

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    I don't know much about engines, but I guess these two were shorting with some wire related to the fans somewhere, causing them not to work.
    Did you try removing them and checking whether the fans work or not?

  3. #3
    The adjustable thermostat you have pictured can not control the fans directly. It needs to run through a relay. Make sure you have power at the relay like this;
    Terminal #87A - not used
    Terminal #30 - 12Volt+ (25amp fused) OR to the fan
    Terminal #87 - Fan OR 12Volt+ (25amp fused)
    (You can mix up the 30 and 87 as long as one goes to the fan and one gets a solid 12+.)

    Terminal #85 and #86 can also be mixed up.
    You need to determine if the thermostat wires control the ground circuit or the positive circuit.
    If the thermostat controls the ground circuit it will look like this;
    Chassis ground - thermostat in - thermostat out - #85 or #86
    #85 or #86 - ACC or IGN fused - 5 amp fuse.
    If it controls the positive circuit then the 12V+ goes - thermostat in - thermostat out - #85 or #86
    and #85 or #86 goes direct to ground.
    Either way is fine.
    HOWEVER, if it were me I would join both thermostat wires together and make sure everything is working before my next trip.
    Run it joined together for a few days before reconnecting the thermostat switch, it could be defective.

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    If your engine idles different after overheating you've blown the engine

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    cutlass422....Oh man, I hope it's not the case, today I will restart it again and see. What should I look for to know if I damaged the motor.
    Xengs, I did try to unplug those too, but it didn't change anything.
    Jim. thank you for the detailed explanation but, I wish I can understand it better. Connect the wires of the thermostat in the motor together? Or the adj.thermostat that controls the fans?
    Should I look for a blown fuse somewhere or a relay? I looked around and checked both batteries and could not find a separate fuse box or separate wire with a fuse leading to the fans.

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    I joined both wires together on the thermostat dial pictured above, fans turned on for a second and pooped a fuse. Which was 20amp fuse and I replaced it. So I assume that was the fuse for the the fans.
    Turns one wire that says chock also says water pump on it(couldnt read what it says first) and when I saw it disconnected I plugged it into a non-working terminal, which explains why the motor sounded different on start up. Fans were not turning on because the rear thermostat was not reading high temperature since there was no coolant flow in the radiators.
    I started the car up and test drove it, sound it much better , temp right at 180 and rear fans working now. Thanks for all the help, I still gotta figure out where to plug in the fog lights now.
    Last edited by redhammer; 07-23-2013 at 10:56 AM.

  7. #7
    A 20amp fuse running your fans is probably too weak. An initial start up of the fans will pull (2 fans) about 30amps.
    I would install a 30amp circuit breaker instead of a fuse. A breaker is a metal box looking fuse.

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    Thanks Jim,
    I test drove it again and after a while it started to overheat again, My friend thinks it sucked air and created an air lock when it overheated the day before and it needs to be burped. How do I properly burp the system with electric water pump. I have 3 radiators, 2 in the rear, one in the front, coolant filler is in the engine compartment, overflow bottle is in the front compartment. I was reading online for cars with electric water pumps you can just run the water pump independently without starting the car to bleed the air out.
    Last edited by redhammer; 07-24-2013 at 08:57 AM.

  9. #9
    Senior Member satinta's Avatar
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    I get air bubbles in my LT1s when I work on them so I fill the coolant as the engine runs through the radiator cap. When it starts to get warm the coolant starts overflowing and I real quick put the cap back on and turn off the engine.
    Let it cool down a couple of hours and do it again. Repeat the process maybe 4 or 5 times until there is no more room in the radiator to add coolant
    I suppose you don't have to run the engine since you have the electric pump but I'm told the proper way is to come up with a valve on the radiator hose or heater hose that is higher then any other point of the cooling system and fill it from there.

  10. #10
    Senior Member satinta's Avatar
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    BTW
    If you start the engine with the radiator cap off and suddenly lots of bubbly foam or brown oil sludge starts coming out of the radiator you do have a blown gasket or crack in the engine.

    I really don't believe it's damaged if you only ran it for 5 minutes at 250 or less...
    Last edited by satinta; 07-24-2013 at 11:00 AM.

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