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Old 07-13-2011, 10:08 AM
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Electric Fans on/off

I've got electric fans hooked up and running fine. They switch on @ ~200* and then off at 180* or so. I've got the switch ignition ran to the ACC fuse under the dash. When the motor is on, the fans stay on constantly no problem when it reaches the temp. Have dual fans running on a single relay.

When I shut the car off on hot days, I turn the key back to the on position for a little while to let the fans cool down the motor some. But when it's in the on position, the fans turn on for about 30-45 sec or so, then shut off. Stay off for a minute or so, then repeats itself. I feel like this should stay on for a longer time to actually get some cooling done.

The sensor is a push in probe-style (which I know aren't the best) located at the top of the radiator right under the radiator hose. Should I move the probe to a different location? Or do these relays auto shut off when seeing just 12v? Thanks!

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Old 07-13-2011, 12:16 PM
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I'll answer your last first. Move the probe to either the radiator bottom tank - you can adapt the petcock fitting - or better, to a temp pickup location near the outlet of the intake manifold. Painless Wiring have a screw in probe with several adapters that works well. SUMMIT has it here.

Now, the cycling - the top tank may not always be totally full - if there is any air, that's where it will end up. Additionally, the thermostat might be cycling as well, allowing spurts of hot water as well as the normal convection flow. That probe to work correctly needs to be flooded at all times
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Old 07-13-2011, 12:54 PM
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Quote:
Originally Posted by Irelands child
I'll answer your last first. Move the probe to either the radiator bottom tank - you can adapt the petcock fitting - or better, to a temp pickup location near the outlet of the intake manifold. Painless Wiring have a screw in probe with several adapters that works well. SUMMIT has it here.

Now, the cycling - the top tank may not always be totally full - if there is any air, that's where it will end up. Additionally, the thermostat might be cycling as well, allowing spurts of hot water as well as the normal convection flow. That probe to work correctly needs to be flooded at all times
I originally was going to buy one that goes on the intake, but it only had 2 open ports and both were going to get used (stock dummy light and temp gauge for sensor). I didn't think that one all the way through to well, so got the easy probe.

I'll try it in a lower position and see if that helps. I thought it may have had to do with the coolant not being there, but figured the fins would still be hot. Thanks.
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Old 07-13-2011, 01:25 PM
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Quote:
Originally Posted by david-b
When I shut the car off on hot days, I turn the key back to the on position for a little while to let the fans cool down the motor some.
i debated this when i first had my truck running. my thoughts are: you won't cool the motor, only the radiator. no circulation, no motor cooling. and: other than those little 4 banger aluminium block cars, oem fans do not cycle on.

as for the sensor location: i had no optional port available. i used a short piece of ss tube in the lower rad hose, welded half a ss pipe coupling in it and placed my sensor there. i figured; let the radiator do it's job. if the coolant coming out is still hot, then turn the fan on.

ironically, i ran hrpt in 100+ heat with the ac running and had no overheating problems. after indy the weather cooled off, i turned the ac off and it spewed coolant at the first stop light. the sensor had come un-plugged.
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Old 07-13-2011, 01:38 PM
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Quote:
Originally Posted by ogre
i debated this when i first had my truck running. my thoughts are: you won't cool the motor, only the radiator. no circulation, no motor cooling. and: other than those little 4 banger aluminium block cars, oem fans do not cycle on.
The fans still cycle the air out of the engine bay though, allowing less heat soak of parts which is why I wanted to keep them on for a little.
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Old 07-13-2011, 02:19 PM
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This is an early photo of mine - the fan sensor is shown, the temp gauge sensor is ~2" directly behind that one and in the manifold:

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Old 07-14-2011, 07:49 AM
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Ogre is right on. You are only cooling the radiator coolant not the engine. I run an electric water pump with an optional switch I can turn on after shutting down to keep circulation going and allowing the fans to do their job. Fans are connected to a circuit that is hot even when the ignition switch is off and a switch that turns on at 190 and off at 175. After shutdown it only takes about 20 seconds for complete cooldown.
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Old 07-14-2011, 10:21 AM
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Sounds like a pretty neat setup. I will try placing the sensor down low to see what happens. I was thinking of wiring it directly to the battery so it can cool down after shut off. Even if it is just coolant the way it is. I feel better. I have a cowl hood on this car and when closed and fans are on (after shutoff) you can feel the heat being pushed out of it.

I imagine since it's a relay and should ideally cut off any power, if I wire it directly to a constant source to stay on after shutdown until it hit 180*, will it have any sort of drain on the battery?
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Old 07-14-2011, 12:22 PM
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Depends on how long it runs. As I said, mine cools down really quick with both the fan & water pump running. The only thing I have to do is manually turn off the WP as it is not hooked to a temp switch. I have no trouble with battery drain.
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Old 07-15-2011, 12:47 PM
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The water in the radiator is not isolated -- even without a pump to circulate the water, convection will effect cooling, albeit, quite a bit slower than with a pump.
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