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Discussion Starter #1
I bit the bullet and ordered a 180F thermostat to install with my new water pump, but before I could get it in (giggity), I had second thoughts and ended up buying a 190F thermostat to try 1st.

After a couple thousand miles, I’m surprised by some odd behavior which seems impossible but obviously it isnt - my cooling fans mounted to the back of the radiator have stopped coming on.

I dropped all the fan settings by 10F using my tuner, so I honestly thought the fans’ behavior wouldn’t change. However, I seem to have found some kind of weird equilibrium with engine temp and ambient temp that combine to make it so there is little to no need for the fans anymore...at least until summer. (But I’ll be installing the 180F then, so this is only going to be temporary at best.)

Anyone else tried a 190F in their Hemi and observed similar fan behavior?
 

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You should be ok with the 190 unit, but its not good to run the car under normal op temp for long durations of time and its actually good on the entire car to get it nice and warm.
160-180 for example can be too cold for most street applications. engine makes poor fuel economy, doesnt burn off residuals both in the oil & fuel, can effect heater/defrost function and I have heard of guys popping all sorts of "out of range/below range" trouble codes ( #1281, #0125 & #0126 for example), as well as eventual cat & evap issues. You also may have emission testing issues if applicable. You want the car to run & maintain a consistant temp, optimal for efficientcy, fans, thermo, rad collant, etc all work to do that collectively.
 

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Discussion Starter #3
You should be ok with the 190 unit, but its not good to run the car under normal op temp for long durations of time and its actually good on the entire car to get it nice and warm.
160-180 for example can be too cold for most street applications. engine makes poor fuel economy, doesnt burn off residuals both in the oil & fuel, can effect heater/defrost function and I have heard of guys popping all sorts of "out of range/below range" trouble codes ( #1281, #0125 & #0126 for example), as well as eventual cat & evap issues. You also may have emission testing issues if applicable. You want the car to run & maintain a consistant temp, optimal for efficientcy, fans, thermo, rad collant, etc all work to do that collectively.
Yeah, that’s why I hesitated with installing the 180F, I didn’t think the cooler weather would allow for it to get up to 100C and stay there long enough to burn off all the moisture and gasoline that polluted it over time.

However, I think with the summer time temps here will allow it to even with the 180F in and I plan on testing that, but I will definitely keep my eye on the oil temps to verify they are getting to 100C and staying there long enough.
 

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Im pretty sure my fans kick on about 207-209. (may vary by model)
I agree, winter temps may not be the best time to test things out to get a real good base.
Like you, I prefer a cooler running car. 200-203 seems ideal for me.
 

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I bit the bullet and ordered a 180F thermostat to install with my new water pump, but before I could get it in (giggity), I had second thoughts and ended up buying a 190F thermostat to try 1st.

After a couple thousand miles, I’m surprised by some odd behavior which seems impossible but obviously it isnt - my cooling fans mounted to the back of the radiator have stopped coming on.

I dropped all the fan settings by 10F using my tuner, so I honestly thought the fans’ behavior wouldn’t change. However, I seem to have found some kind of weird equilibrium with engine temp and ambient temp that combine to make it so there is little to no need for the fans anymore...at least until summer. (But I’ll be installing the 180F then, so this is only going to be temporary at best.)

Anyone else tried a 190F in their Hemi and observed similar fan behavior?
My observation with my Hellcat is with the factory T-stat the coolant temperature remains quite low when driving on the highway. The oil temperature likewise.

Around town the coolant temperature climbs and on hot days can climb to 216F at which point I believe the radiator fan comes on. (However, on "really" hot days I have the A/C on which runs the radiator fan all the time and this works to keep the coolant way below 216F, down around the 200F to 203F range.)

I just can't see any benefit to a lower temperature T-stat given how cool these engines run, at least based on my observation of my Hellcat's engine.

If I was to make any change to the cooling system of my Hellcat I'd just lower the temperature at which the radiator fan came on. Say change it from 216F to 212F. I would also lower the temperature at which the fan shut off. For example with my previous cars the fans would come on at 212F and shut off at 205F.

Even so in extremely high ambient temperature -- 116F -- the coolant temperature climbed to 226F. A lower temperature T-stat would not have helped. At that temperature the factory T-stat was wide open.

The "problem" was the amount of cooling capacity. That the coolant temperature reached 226F but stayed there (and another time I tried to get the coolant to get hotter and was unable to) clearly indicated to me to keep the coolant temperature from obtaining that temperature was that more cooling capacity was needed. Now the car was equipped with 2 separate radiators and both backed by a radiator fan.

But another car with a bigger engine (and turbo charged) ran much cooler. It had 2 radiators each backed by a fan and a 3rd radiator mounted between the two other radiators (but with no fan) and much better aerodynamics and even in 119F ambient temperature being driven in the same way ran much much cooler. Just more cooling capacity and better aerodynamics to allow for more air flow through the radiators was the difference. Same T-stat. Same fan on high temperature and shut off temperature thresholds: 212F and 205F.
 

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Discussion Starter #6
Given the fact that your Hellcat’s engine has a MAF, I can see where lowering the operating temperature wouldn’t have much effect - it’s smart enough to realize exactly how much air is coming in regardless of the temperature of said air.

I’m still stuck with the Speed Density system though, so when the IAT tells my PCM the incoming air charge is 150F despite the fact I’m no longer idling in a drive thru line, it’s only gonna spray enough gas to mix with air that’s 150F.

My hope is not that my IAT will suddenly resist heat soak and begin reporting accurate temperatures to the PCM, it is that the lower operating temp of the engine will impart less heat onto that IAT, thereby lowering the delta between reported and true incoming air charge temperature.
 

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Discussion Starter #7
One detrimental side effect of this lowered engine coolant (and therefore engine) temperature is that it’s much more difficult to heat up my meals on long highway trips. While that’s certainly an inconvenience, it’s not enough of one to make me switch back just yet...
 
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