Weird, Overheat AC controls thermostat

[jjcuff1]

94 S del sol manual with AC

 

but a new radiator cap on it and during city driving and bumper to bumper car thermostat sits at 40% on temp gage. maybe 50% with AC on.

 

once I drive on the highway, seems like specific amount, like 20-30 minutes at 70mph the thermo rises quickly to 90%.

 

I tried with and without AC on it does the same thing.

 

As soon as I switch the AC control over to the red/hot side (this is with no vent selector pushed)

 

the temp gage drops down to below 50% again.

 

seems like on the highway the engine bay is starving for air flow or the sensor is in a hot spot and when I turn the heat on more air is exchanged from the cabin? Where when it is on cold side that vent is blocked off?

 

 

as soon as I get off highway even in TRAFFIC the temp drops back down...

[mustang_eater12]

it sounds like your thermastat is gettin stuck. most of the time when your drivin at a contant speed the temp of your engine will be cooler before you bring it up to speed. as soon as you bring the temp up the thermastat will get stuck in the closed position. when your drivin through town your engine temp is goin up and down. thus the thermastat has more coolent passin by it to heat it up slowly. if changin your thermastat doesnt change anything check you temp sensor.

[TS John]

You're a pretty knowledgable dude. Stick around, Kegan's brother.

 

Also, tell us your name so we can call you something besides that.

[90IntegraC1]

your thermostat is stuck closed on the highway...replace it.

 

check if your cooling fan is going on as well, your fan switch may have gone bad on the back of the block.

[jjcuff1]

ok brand new cap, so thats not it and it did work better since in the city with the new cap it stays around 30%-40% with AC.

 

Fan runs at idle in driveway, I was wodering if it shuts off on highway.

 

All signs point to temp sensor.