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Electric fan + 4.0 liter owner question: what temp?

NashvilleTJ

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What? In what situation is your radiator coolant hotter than your engine?

The coolant is heated by the engine so it shouldn't be any hotter than the engine.

I don't think the coolant going in would ever be hotter than what's coming out. On the contrary, I don't think dumping a radiator full of cold coolant into a hot engine is probably very good for it.

Good points all - misstatement on my part. I guess what I should have said is having the coolant come out of the radiator at a temperature higher than the thermostat.

Since the thermostat sets the lower limit and the fan sets the upper limit, setting the fan below the thermostat just makes it so the fan is always on. I'd rather get at least some range where the fan isn't running. I don't think I'd go to 221 though, I'd probably stick with 210. Unless it was variable speed and I could set a proportional band to first turn on at minimum speed in the low 200s and max out at 215-220 or something.

I've never thought the fan sets the upper limit. If that were the case nothing would change if you removed the thermostat, other than it would take longer to reach operating temp. In all my experience if you remove the thermostat from a properly operating cooling system, the engine will run cooler.

But thinking about that - maybe that explains why the 4.0 runs at 210 with a 195 degree thermostat???

A while back on my rig, I had the thermostat fail and it overheated. I removed the thermostat expecting it to run cooler - it did not. I interpreted that as my cooling system not having enough excess capacity. I then swapped in a much more powerful e-fan. Now without a thermostat it runs in the 160 range. With the 180 degree thermostat in there it runs consistently at 183-185.
 
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freedom_in_4low

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Good points all - misstatement on my part. I guess what I should have said is having the coolant come out of the radiator at a temperature higher than the thermostat.



I've never thought the fan sets the upper limit. If that were the case nothing would change if you removed the thermostat, other than it would take longer to reach operating temp. In all my experience if you remove the thermostat from a properly operating cooling system, the engine will run cooler.

But thinking about that - maybe that explains why the 4.0 runs at 210 with a 195 degree thermostat???

A while back on my rig, I had the thermostat fail and it overheated. I removed the thermostat expecting it to run cooler - it did not. I interpreted that as my cooling system not having enough excess capacity. I then swapped in a much more powerful e-fan. Now without a thermostat it runs in the 160 range. With the 180 degree thermostat in there it runs consistently at 183-185.

I should have said the fan attempts to enforce an upper limit, rather than setting it. Or said another way, it applies a decreasing influence on the temperature, while the thermostat applies an increasing influence on it. I make a point in my work to avoid giving two such devices any overlap in the control range, and I have literally perfect analogs to this where I use fans to cool a fluid and a valve to enforce a lower limit. If I let them overlap, then as soon as it gets cold the fan will ramp up to the max and the valve will end up modulating to control the temperature.

Ultimately, the cooling system has a load, which is the actual BTU/h or watts of heat being put into the coolant in the engine water jacket. A radiator at a given air and coolant flow rate rejects heat with a (close enough to) linear relationship to the temperature difference between the coolant and the air. In steady state operation, heat in = heat out, so the ECT will "find" and stabilize at whatever temperature difference above ambient results in the radiator rejecting the same amount of heat that the engine is putting out. If it's cool outside, the engine is at low load, that temperature will be below the thermostat setting; the thermostat closes to reduce flow through the radiator to make the heat balance at the larger temperature difference.
 

Blackjack

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Someone please educate me on this one, as I‘ve never understood the logic of having the fan come on a a higher temp than the engine thermostat. Although I have read of custom radiator companies making this very recommendation.

I don’t want the radiator dumping coolant into the engine that is hotter than the engine - that make no sense to me. I run a 180 degree thermostat (easy fellers, remember I’m not running a 4.0🙂) and a 170 fan controller - which works very well for me.

I run a variable speed fan which does usually run at low speed, but rarely at full speed. But it’s certainly not a daily driver, so I’m not worried about fan life.

So help a guy out: What am I missing here?

The fan is there to provide air movement when vehicle speed is low enough to not push an adequate amount through the radiator. Since most fan controls measure the water temp if you set it too low it will be trying to engage the fan when it may not be necessary.
 
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Blackjack

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I've never thought the fan sets the upper limit. If that were the case nothing would change if you removed the thermostat, other than it would take longer to reach operating temp. In all my experience if you remove the thermostat from a properly operating cooling system, the engine will run cooler.

But thinking about that - maybe that explains why the 4.0 runs at 210 with a 195 degree thermostat???

A while back on my rig, I had the thermostat fail and it overheated. I removed the thermostat expecting it to run cooler - it did not. I interpreted that as my cooling system not having enough excess capacity. I then swapped in a much more powerful e-fan. Now without a thermostat it runs in the 160 range. With the 180 degree thermostat in there it runs consistently at 183-185.
In older vehicles they built with more than adequate cooling capacity but with more stringent emission standards they found that running the engines at higher operating temps combined with leaner air fuel ratios helped with some combustion gas control. You can see this in the difference between the 4.0 in a YJ vs one in an 2004 TJ. YJ runs a old fashioned copper radiator and richer A/F ratios and rarely see overheating and the TJ runs much leaner and at the upper most limit of the cooling systems capability. This is an oversimplification of course but you get the idea.
 

Mikee024

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Yes as above a 195 degree thermostat is correct. You definitely don't want the electric fan running 100% of the time so I'd be looking for it to turn on above 210, one post I read said 221 degrees which sounds reasonable to me.

There's a balance to the dance, and I'd rather not wait for the fan to kick on when my engine is already at 221*. There might be days where the engine peaks around 221* even if my e-fan kicks on at 210 or so.

The goal is to maintain a happy engine temp., but also not overstrain the E-fan components (to Jerry's point).

A decent E-fan will handle cycling on at let's say 210-215 and then shutting off around 195 to 200 only to be kicked back on again minutes later. The world is packed with modern vehicles running E-fans that way (many idling or in high-dense traffic while running A/C on a hot summer day). You hear the fan kick on, then it kicks off (only to come back on again seconds/minutes later).

I simply went with Mopar parts because I wanted a no-fuss proven setup that would handle offroading in the desert.
 

Apparition

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In older vehicles they built with more than adequate cooling capacity but with more stringent emission standards they found that running the engines at higher operating temps combined with leaner air fuel ratios helped with some combustion gas control. You can see this in the difference between the 4.0 in a YJ vs one in an 2004 TJ. YJ runs a old fashioned copper radiator and richer A/F ratios and rarely see overheating and the TJ runs much leaner and at the upper most limit of the cooling systems capability. This is an oversimplification of course but you get the idea.

This is also what I’ve been reading. I know my LS comes factory set to turn on the fan at 207° F coolant temp. 187° F thermostat.
 

Apparition

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This is all quite interesting. Smarter Every Day.

1664237888830.gif
 
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imactj2004

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Most definitely stick with a 195 thermostat. For a non adjustable switch I would try a 205 degree on and see how that works. I run an adjustable fan control with a cutoff so I can adjust for seasons or conditions.

Mind sharing the model unit for the adjustible control?
 
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imactj2004

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The stock viscous fan engages with a radiator leaving air temp of about 170, so I would want a switch that switched at an ECT that corresponded with that. Previous posters suggesting in the 210 range are probably right on the money.

Yeah, thats the crux of what I’m try to figure out: what ECT temp corresponds to the OEM air temp. It is sounding more and more that the answer from others is 210.

I dont know why, but that seems odd to me. For example, lets take the e-fan out of the equation for a moment and focus on the OEM fan. If we assume that 170 radiator temp corresponds to 210 ECT temp, then that would mean that the OEM fan turns on as soon as the vehicle reaches operating temperature. But Is this true? Is this how the oem fan behaves? Or is that clutch engaging when the ECT hits a higher threshold, say of 215 or 220, to bring the ECT back to 210? I have never owned or ridden in another jeep so Im genuinely curious and I’d like to try to match whatever range the oem setup is doing.

Side note for those who may not have read the backstory in another thread: I inherited this vehicle from my father n law, who liked to “do things his way”. He installed the efan, had a165 t-stat (!) and a fan sensor switch set to engage at 185. With that setup, the jeep ran at a consistently cool185-190…BUT…threw a code for “vehicle running cold too long” which is a barrier to passing a smog test here in California. I’ve now replaced that t-stat with the recommended 195 and a fan switch set to engage at 210 to bring it down to 195. I was skeptical of these numbers at first but sure enough, that t-stat opens up at 195 and the fan turns on at around 212-215 on the gauge before turning back off at 205-210. It doesnt ever really get back down to 195 but that’s okay, it also doesnt creep over 215. The observations from these two t-stat and fan switch settings is that the gauge runs at approx 20 degrees over the t-stat and the fan engages at approximately 5-10 over the stated threshold for the switch. I’m assuming that the delay in fan engagement is a result of sensor timing which is fine. I can live with that 5 degree variance in the current setup.

However, this brings me back to the question of corresponding ECT temps and behavior. If the oem fan turns on when ECT reaches 220 at the gauge then I do get nervous with the idea of getting a fan switch that is set to engage at 220 and off at 205. Based on observations, that would result in the fan not coming on until ECT hits 225 (or maybe higher) and probably not be capable of actually dropping back down to the targeted 205. Those ranges are outside my comfort zone.

All of the above are why a variable control unit is sounding more and more appealing to me.

And yes, I know that I go back to factory setup. That’s just not on the table at this point. Maybe in the future. For now, I need to pass emissions while not blowing a gasket.
 
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Blackjack

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Blackjack

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Yeah, thats the crux of what I’m try to figure out: what ECT temp corresponds to the OEM air temp. It is sounding more and more that the answer from others is 210.

I dont know why, but that seems odd to me. For example, lets take the e-fan out of the equation for a moment and focus on the OEM fan. If we assume that 170 radiator temp corresponds to 210 ECT temp, then that would mean that the OEM fan turns on as soon as the vehicle reaches operating temperature. But Is this true? Is this how the oem fan behaves? Or is that clutch engaging when the ECT hits a higher threshold, say of 215 or 220, to bring the ECT back to 210? I have never owned or ridden in another jeep so Im genuinely curious and I’d like to try to match whatever range the oem setup is doing.

Side note for those who may not have read the backstory in another thread: I inherited this vehicle from my father n law, who liked to “do things his way”. He installed the efan, had a165 t-stat (!) and a fan sensor switch set to engage at 185. With that setup, the jeep ran at a consistently cool185-190…BUT…threw a code for “vehicle running cold too long” which is a barrier to passing a smog test here in California. I’ve now replaced that t-stat with the recommended 195 and a fan switch set to engage at 210 to bring it down to 195. I was skeptical of these numbers at first but sure enough, that t-stat opens up at 195 and the fan turns on at around 212-215 on the gauge before turning back off at 205-210. It doesnt ever really get back down to 195 but that’s okay, it also doesnt creep over 215. The observations from these two t-stat and fan switch settings is that the gauge runs at approx 20 degrees over the t-stat and the fan engages at approximately 5-10 over the stated threshold for the switch. I’m assuming that the delay in fan engagement is a result of sensor timing which is fine. I can live with that 5 degree variance in the current setup.

However, this brings me back to the question of corresponding ECT temps and behavior. If the oem fan turns on when ECT reaches 220 at the gauge then I do get nervous with the idea of getting a fan switch that is set to engage at 220 and off at 205. Based on observations, that would result in the fan not coming on until ECT hits 225 (or maybe higher) and probably not be capable of actually dropping back down to the targeted 205. Those ranges are outside my comfort zone.

All of the above are why a variable control unit is sounding more and more appealing to me.

And yes, I know that I go back to factory setup. That’s just not on the table at this point. Maybe in the future. For now, I need to pass emissions while not blowing a gasket.

Like I mentioned earlier try a 205 degree switch.
 

freedom_in_4low

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Yeah, thats the crux of what I’m try to figure out: what ECT temp corresponds to the OEM air temp. It is sounding more and more that the answer from others is 210.

I dont know why, but that seems odd to me. For example, lets take the e-fan out of the equation for a moment and focus on the OEM fan. If we assume that 170 radiator temp corresponds to 210 ECT temp, then that would mean that the OEM fan turns on as soon as the vehicle reaches operating temperature. But Is this true? Is this how the oem fan behaves? Or is that clutch engaging when the ECT hits a higher threshold, say of 215 or 220, to bring the ECT back to 210? I have never owned or ridden in another jeep so Im genuinely curious and I’d like to try to match whatever range the oem setup is doing.

Side note for those who may not have read the backstory in another thread: I inherited this vehicle from my father n law, who liked to “do things his way”. He installed the efan, had a165 t-stat (!) and a fan sensor switch set to engage at 185. With that setup, the jeep ran at a consistently cool185-190…BUT…threw a code for “vehicle running cold too long” which is a barrier to passing a smog test here in California. I’ve now replaced that t-stat with the recommended 195 and a fan switch set to engage at 210 to bring it down to 195. I was skeptical of these numbers at first but sure enough, that t-stat opens up at 195 and the fan turns on at around 212-215 on the gauge before turning back off at 205-210. It doesnt ever really get back down to 195 but that’s okay, it also doesnt creep over 215. The observations from these two t-stat and fan switch settings is that the gauge runs at approx 20 degrees over the t-stat and the fan engages at approximately 5-10 over the stated threshold for the switch. I’m assuming that the delay in fan engagement is a result of sensor timing which is fine. I can live with that 5 degree variance in the current setup.

However, this brings me back to the question of corresponding ECT temps and behavior. If the oem fan turns on when ECT reaches 220 at the gauge then I do get nervous with the idea of getting a fan switch that is set to engage at 220 and off at 205. Based on observations, that would result in the fan not coming on until ECT hits 225 (or maybe higher) and probably not be capable of actually dropping back down to the targeted 205. Those ranges are outside my comfort zone.

All of the above are why a variable control unit is sounding more and more appealing to me.

And yes, I know that I go back to factory setup. That’s just not on the table at this point. Maybe in the future. For now, I need to pass emissions while not blowing a gasket.

Well, it's not technically possible to truly duplicate a viscous fan drive with ECT. Unlike with temperature difference, the radiator heat transfer capacity is not linear with airflow, and the "air off" temperature (air coming out of the radiator) is going to be a function of the ECT, ambient, and airflow...it ends up being a system of equations to solve with linear algebra to find where everything lands.

Where that manifests itself is when you consider that ECT doesn't respond as directly to airflow as air off temp does, you can be cruising down the hwy with high engine load and be running the fan because the ECT is high, even though there's so much air moving that the fan isn't accomplishing anything, and the air off the radiator is cool enough that a viscous clutch would be disengaged. Conversely, you'll be sitting in a drive through on moderate temperatures that a fan clutch would partially engage and hold you right at the thermostat setting but the e fan will let it go to 210, pull it down and then cycle repeatedly.

I kinda lost track of where I was going with that but I'm leaving it because I think it's worth pointing out that there is no ECT that's always analogous to a viscous fan clutch reaching 170.

Back to your question though, yes if I wanted the engine to stay at 210 or below, I would turn an on/off fan on at 210 and off at something like 200, and if I had a variable speed fan, I would probably start it at 200-205 and reach max speed at 210-215 and play with the settings until I found a point where I liked it.
 
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JustDandee

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A couple of thoughts :Fan clutch has a thermostatic spring on the front allowing it to more or less free wheel and tighten up as it gets hotter. A very old and reliable design but the do wear out. that mechanical fan is always turning its load may vary but it’s always moving something

When using a radiator probe fan controller(stuck through the radiator fins) you install at the top of the radiator near the water inlet. So you are wanting to be using the coolants exit temperature to activate the switch. If you are using a fixed setting switch then Ideally it is up in the head near the exit to capture the exit temp. Something to consider.

Personally I like a good electric system- the payoff here is when winter temps turn to single digits that engine gets up to temp a little quicker- .
 

Wildman

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I know you have a new sensor coming but the other option is to use a PWM fan controller like this Spal unit that I was using on mine. I have a V-8 swap and went with electric fans. This controller allows you to set the temp you want the fan to come on at 50% and then it slowly increases to 100% when it reaches the next set temp. This unit isn't made anymore but Dakota Digital offers one.

1664394914908.png


It uses the stock temp sensor and takes a reading from it.

https://www.amazon.com/dp/B07W3PCXZK/?tag=wranglerorg-20

Or this one from Derale

https://www.amazon.com/dp/B00N0N75TI/?tag=wranglerorg-20

They aren't inexpensive but do give you more control over your fan.