Cylinder Head Temp question.

I recently noticed that the average cylinder temp is higher when the A/C is off.
It usually stays 207-210 when the a/c is on, and i ve seen it raising up to 219 when the ac is off while I was parking my car in to the garage. Does a/c cools down the head temp? and is it normal and fine to have 219 temp? Because it raises up high when I park, I tend to wait till it goes down to 208 and shut the car.
Thanks in advance!

Turning the AC on turns on a radiator cooling fan which in turn may lower head temps. Changing the thermostat to a 170 deg will help. My temps are usually 190 with the 170 thermostat.

Turning the AC on means there's energy exchange happening in the condenser, which is right in front of the radiator. This will usually raise coolant temps slightly.

What you're seeing is the engine being fully up to temp, slowing down (which reduces airflow across the radiator and condenser), and thus getting a mild heat soak. The fan will kick on at that point and bring it back down to 207-208 F. I would look at your coolant levels. Mine was running about where yours was till I added a bit more coolant (sits nearly at Max line when hot, drops to a bit above Min when cold). This dropped temps about 5-7 deg.

rollingshi59 said:

I recently noticed that the average cylinder temp is higher when the A/C is off.
It usually stays 207-210 when the a/c is on, and i ve seen it raising up to 219 when the ac is off while I was parking my car in to the garage. Does a/c cools down the head temp? and is it normal and fine to have 219 temp? Because it raises up high when I park, I tend to wait till it goes down to 208 and shut the car.
Thanks in advance!

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normal. My CHT can climb to 225F when parked.

raycer said:

Turning the AC on turns on a radiator cooling fan which in turn may lower head temps. Changing the thermostat to a 170 deg will help. My temps are usually 190 with the 170 thermostat.

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I doubt 170 themostat will do anything. I think stock thermostat is 180, and CHT are above that, so the thermostat should be wide open.

Stock cars don't overheat on the street. That's why they're tested in death valley and work fine in AZ, Vegas, TX, FL, etc... They don't "need" lower thermostats. If they were needed, Ford would have installed them.

mustang1 said:

normal. My CHT can climb to 225F when parked.



I doubt 170 themostat will do anything. I think stock thermostat is 180, and CHT are above that, so the thermostat should be wide open.

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CHT is normally 9-11 degrees above the coolant temp.


The 170 thermostat with a tune to match will keep your head temps around 190-200 always. I've seen 201 a few times since putting in the 170 and that's only in traffic on a super hot day. Normally when driving it's around 190-194 CHT.

My car isn't even a PP with the larger radiator so that helps even more.

Dr. Norts said:

The 170 thermostat with a tune to match will keep your head temps around 190-200 always. I've seen 201 a few times since putting in the 170 and that's only in traffic on a super hot day. Normally when driving it's around 190-194 CHT.

My car isn't even a PP with the larger radiator so that helps even more.

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My CHT are around 195F on the freeway, 205-215F in stop & go. And 225F after its parked. At least when its hot outside. Can't imagine changing thermostat from 180->170 will somehow drop these temps.

mustang1 said:

My CHT are around 195F on the freeway, 205-215F in stop & go. And 225F after its parked. At least when its hot outside. Can't imagine changing thermostat from 180->170 will somehow drop these temps.

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You don't have to imagine. There are tons of members here that can validate that for you with real life results.

A 170 stat with a tune and supporting fan settings will get you sub 200 CHTs all day.

Dr. Norts said:

You don't have to imagine. There are tons of members here that can validate that for you with real life results.

A 170 stat with a tune and supporting fan settings will get you sub 200 CHTs all day.

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What's the point? Other than to be below some arbitrary temperature that you "feel" is too hot?

The car is designed to work at the temps people are "worried" about. There's a reason the fans come on at the temps they do, and the thermostat is fully open at the temp it does. Since the car cools back down when the OEM fan kicks on mean the system is cycling and working as designed.

Lower thermostats don't prevent (or have any impact on) the car overheating when pushing the car hard at the track on a hot day.

Eritas said:

What's the point? Other than to be below some arbitrary temperature that you "feel" is too hot?

The car is designed to work at the temps people are "worried" about. There's a reason the fans come on at the temps they do, and the thermostat is fully open at the temp it does. Since the car cools back down when the OEM fan kicks on mean the system is cycling and working as designed.

Lower thermostats don't prevent (or have any impact on) the car overheating when pushing the car hard at the track on a hot day.

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You're completely right, stock.

For a tuned car, lowering the CHTs will net a little more power. Too much, though, and you'll reduce. It's a fine balance.

Livernois tell you that?

Eritas said:

Livernois tell you that?

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The timing / ect table tells you that.

Lower engine coolant temp = more timing advance

Dr. Norts said:

The timing / ect table tells you that.

Lower engine coolant temp = more timing advance

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So what is the temp range where you can add more timing than at 200-210*F CHT?

ideal engine temperature probably starts at 190F.

205-225F may not be ideal, but that's the domain of the stop & go, and parking. Where it doesn't matter.

Being in S Florida I changed mine to the 170* stat... Head temps went down like 20* which is what I wanted them to, though some say its not needed I feel its a plus.

Computer controlled cars usually will retard timing as temps increase, S Florida is ALWAYS Hot so any little bit of cooling help is welcomed and thus will keep power where it should be. Ford builds their cars to satisfy ALL environments and the perfect balance for them maybe 190* as it helps them achieve the emissions standard they have to meet, doesn't mean that is what is best for performance.

I'm NO engineer but I believe in keeping things simple and being a bit proactive.


L8R