When should electric fans come on?

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merrill77
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When should electric fans come on?

Postby merrill77 » Thu May 03, 2018 7:57 am

My 77 has aftermarket radiator with dual electric fans. The 401 has electronic FI and ignition and likely a more aggressive cam. It also had a thermostat that was locked wide-open when I got it. The thermostat has been replaced with a stock open-temp (205F?). When observe it warming up, I can feel when the thermostat opens - first I can feel the flow in the hose and then the aluminum radiator warms almost immediately where the coolant enters the radiator. The electric fans came on a minute or two before the thermostat opened. This implies to me that they are set to come on a lower temp than the thermostat. Also implies that they will always run - including at highway speed and even if the thermostat were to close partially - such as getting on the highway with colder air temps. I think they would only ever stop if the ambient was so cold that the engine could not reach operating temperature?

I would have thought that the fans should not come on until the coolant temp is a little above the thermostat open temp.
Am I off-base?

TIA!
Chris

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77 Wagoneer and 97 TJ.

cmaje72
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Location: Western NY

Re: When should electric fans come on?

Postby cmaje72 » Thu May 03, 2018 8:49 am

What turns on the fans the EFI ECU/fan controller or temp switches? It its a temp swtich in the block somewhere they are static and only work in whatever range they were designed for. If its controlled by your EFI ecu or a fan controller then you should be able to modify the settings.
So as an example mine are controlled by the ECU so I can set them to turn on/off at specific temps and also turn off when the vehicle hits a specific speed.
79 Cherokee 5.3/4l65E/NP241C
79 CJ7

RamJetFSJ
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Re: When should electric fans come on?

Postby RamJetFSJ » Thu May 03, 2018 9:08 am

Depending on where the sensor is (if its in the intake manifold near the thermostat), they should come on a bit above your thermostat temp, and turn off a bit below. If you dont have a mechanical fan, they yes, they are going to be running quite a bit, but at freeway speeds, if you motor is running correctly, the water coming out of the radiator should be cold enough to shut off the fans. You can change the fan controller to one that gets its temperature from the radiator fins instead, and that may make it so it doesnt run all the time, and is better for a secondary fan (in addition to a mechanical fan) IMO.
80 Wag in 73 attire, Ram Jet 350 power

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merrill77
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Re: When should electric fans come on?

Postby merrill77 » Fri May 04, 2018 5:01 am

cmaje72 wrote:What turns on the fans the EFI ECU/fan controller or temp switches? It its a temp swtich in the block somewhere they are static and only work in whatever range they were designed for. If its controlled by your EFI ecu or a fan controller then you should be able to modify the settings.
So as an example mine are controlled by the ECU so I can set them to turn on/off at specific temps and also turn off when the vehicle hits a specific speed.


Good question...I will investigate that. It has an Edelbrock Pro Flow 2, which I have not yet learned much about. I am sure there is plenty of info available for it, so that should not be too hard. I'd guess I will also need to follow the wiring to see what the fans are connected to.

Thanks!
77 Wagoneer and 97 TJ.

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merrill77
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Re: When should electric fans come on?

Postby merrill77 » Fri May 04, 2018 5:10 am

RamJetFSJ wrote:Depending on where the sensor is (if its in the intake manifold near the thermostat), they should come on a bit above your thermostat temp, and turn off a bit below.


Thanks...that is what I was expecting.

RamJetFSJ wrote:If you dont have a mechanical fan, they yes, they are going to be running quite a bit, but at freeway speeds, if you motor is running correctly, the water coming out of the radiator should be cold enough to shut off the fans. You can change the fan controller to one that gets its temperature from the radiator fins instead, and that may make it so it doesnt run all the time, and is better for a secondary fan (in addition to a mechanical fan) IMO.


Yeah, I expect they'll be running pretty much full time when I'm running around town this time of year (70-90F ambient temps).

I find myself wondering: Do modern cars have variable-speed fans? Do any dual fan setups use staggered cut-on/off temps?

Anyways...thanks again!
Chris
77 Wagoneer and 97 TJ.

cmaje72
Posts: 179
Joined: Thu Jul 07, 2011 6:33 am
Location: Western NY

Re: When should electric fans come on?

Postby cmaje72 » Fri May 04, 2018 7:46 am

If you follow the power wires from the fan back to (hopefully) the relay that powers it you should be able to determine what turns the fan on and off from there.
79 Cherokee 5.3/4l65E/NP241C
79 CJ7

RamJetFSJ
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Re: When should electric fans come on?

Postby RamJetFSJ » Fri May 04, 2018 9:04 am

merrill77 wrote:I find myself wondering: Do modern cars have variable-speed fans? Do any dual fan setups use staggered cut-on/off temps?
Chris


Variable speed? Yes, they do. Makes the fan much quieter/takes much less power.

This Dakota digital unit is fully tunable, and has a high and low fan control. Although its designed to piggy back off the Dakota digital's temp sensor. https://www.summitracing.com/parts/dak-pac-2750

Ive got a pretty loud primary electric fan on my rig, but the engine and exhaust are loud enough I don't hear it turn on or off. Would be interesting to have a temporary light come on to monitor when its kicking on/off. I bet it will burn out pretty fast if its running ALL the time. I have sat in pretty bad traffic without overheating, and am fine cruising down the freeway for extended periods, but I havent done any wheeling yet to know if my cooling system is sufficient for that.
80 Wag in 73 attire, Ram Jet 350 power


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