Electric fan thermostat question

[Money_pit]

Just installed new champion 3 row aluminium rafiator and their dual fan and shroud combo. I also put in a painless dual fan controller, with the threaded temp switch. The heads I have do not have ports to thread in temp switch. So I bought a thermostat spacer and put my electric fan switch below the thermostat. Should have worked I thought I put in a 190 thermostat. Fan switch cycles 200 on and 175 I think off. Problem is is the truck sits and idles fans will not shut off temps just sit right at 195 no more no less. Am I missing something or over look something I assumed the fans would cycle. Thanks in advance

[Andy4639]

The fans coming on and staying on means the temp isn't going down much are there is a problem with the cutoff temp senor wire. Can you verify the water temp and see if it cools down enough to shut the fans off?

By the way why do you have 2 separate post on this?

[Money_pit]

Sorry must have doubled back and it reposted. For some reason the temp doesn't seem to be coming down with both fans running. The temp gauge will come up to about 205 then fans kick on and will not come back down below 195. This is my first go round with electric fans. So I didn't know if the fan switch and thermostat combo were right or not. I originally had a spacer with the fan switch above the thermostat and same results.

[davepl]

If you have a fan controller is it possible it's running the fans just enough to keep it at your 195 set point? Rather than cutting in and out, it's running at a slower constant rate perhaps?

[Money_pit]

It's just one of those threaded sensors that I thought was supposed to run the fans then they would run long enough then cycle on and off. But that's not my case once they're on they just stay on I've let it idle for a solid 20 minutes and they never shut down. And this is all new everything

[Money_pit]

Just confirmed again truck hits *210 then comes back down once thermostat opens up. Takes about 15 minutes to warm up its only *55 today. Then the fans just don't shut off. Just noticed water pump pulley looks nearly same size as crankshaft pulley. Could that have the affects I'm having by the pulleys being same size?

[Mrturner1]

I just went through the same headache and finally got it figured out, here are some things that I had to check and fix.

Alternator - is it producing enough amperage at an idle speed to power the fans? Dual electric's usually want about 50 to 60 AMPs, and most alternators (aside from high end aftermarket obviously) only make 40 amps at idle speed. The rating on your alternator for amperage output is much different at idle than the one they advertise. Even if you have 100 amp aftermarket alternator, those typically make 60 amps at idle, and that is all shared by your ignition, lights and starter, electric choke, radio or anything else that requires power. This one was hard for me to spot because the fans were still running, but they weren't pushing as much air as they were supposed to. Once you hear the fans at full power you'll know the difference. It's like a house fan on low compared to high.

Another thing to check for like Davepl was saying is that your thermal switch or fan controller isn't limiting the amperage to your fans so that they move slower or less CFM. This would make it get much hotter at idle. You want 2500cfm minimum with these trucks.

On my set up I found that the radiator probe works best for the fan controller switch, but the threaded type might work just as well. I would measure the diameter of your water pump pulley and compare that to factory. And make sure that the power wire for the alternator and the fans is a large enough gauge to carry sufficient amperage. I tried a bunch of different thermostats and found that the 160 made things worse and the 180 was just right. When my truck is idling the fan kick on for about 45 seconds and the truck was down to 180 and runs there for another 10 minutes, slow heats back up after a while and fans kick on again for 45 seconds, cools it down and it's fine for another 10 minutes. That's with an old brass factory radiator and a big lopey cam with tons of initial timing, a set up that is sure to run hot at stoplights lol

Is alternator producing enough IDLE amperage?
Are power wires large enough gauge to carry amperage?
Is fan controller limiting amperage?
Check water pump pulley diameter vs stock pulley
Try 180 t-stat (worked best for me, worth a try)
Verify if fans are pulling or pushing
"Burp" new cooling system of any air (park nose uphill)


Let me know how it goes. Electric fans are awesome, and they work great. Some are going to say the ONLY thing that works is stock shroud with clutch fan, not true. You'll figure this out, it's just picky, and frustrating (trust me I know) because it's all new parts too. Even the peak 210* that your reaching isn't that bad, but you can make it run cooler and have your fans only kick on periodically.

[Money_pit]

Thanks for all the input I have confirmed they are both pulling. Also the alternator is 105 amp I got new. When the fans run at idle I'm showing 13.4-13.6 with a fluke meter. I just wish I remember foresure which thermostat I had in there it must be a 195 I'm gonna drain it down and go grab a 180 see if it will change anything. Thanks again

[kingstrider]

When idling or in stop and go traffic my fan stays on too. Not sure if it cycles when driving or not, cannot hear it over the exhaust.

[Mrturner1]

Originally Posted by Money_pit

Thanks for all the input I have confirmed they are both pulling. Also the alternator is 105 amp I got new. When the fans run at idle I'm showing 13.4-13.6 with a fluke meter. I just wish I remember foresure which thermostat I had in there it must be a 195 I'm gonna drain it down and go grab a 180 see if it will change anything. Thanks again

Is the 105 alternator a Powermaster? You'll want to check the idle speed amperage on it, that's the important info. I just looked at your dog and remembered you from my post about stall converters a while back. Is this the same truck that was in peices not to long ago? If so glad to see you have it together

The 180* thermostat should keep you out of fan operating temp most of the time while idling, but they will always kick on and off.

[Money_pit]

Yep almost road worthy now just to all the odd and ends that are time consuming. Thanks for the help guys putting in a *180 as we speak

[davepl]

If your "OFF" point is at or below the thermostat closing point, and if its based on a sender in the block or head, that temp will never get below the thermostat set point and so they'll never turn off.

In the meantime the fans are performing additional cooling of the water in the rad, but the engine doesn't need/want it until the thermostat opens again.

Consider that the motor (via the thermostat) is doing its best to keep the water in the block over 195F and the fans are trying to cool the rad off to 175, not gonna work. Your off set point still needs to be above the thermostat.

[Money_pit]

Just bought a *180 thermostat and threw it in and I had a load lifted off my shoulders truck sat warmed up fans cycled on and off they run for about 3 minutes and go back off for about 10 minutes. Works awesome thank you guys for your help