Hypothetical Question

[shorty]

170 thermostat, proper coolant mixture, underdrive pulley and no air in the system. Sitting in traffic with the outside temp at 100 the heat goes to 205. I turn off the AC and turn on the heater and the temp starts down almost immediately. Temp goes to 195ish and turning off heater and on the AC, shortly it goes back up to the 205-210 range. Just turning off the AC does not help.

Same temp problem as above happens at 80 mph and I can drop the speed to 65 or repeat the heater scenario as above to lower temp. All this in 100 degree weather. Yes, we do have 80 mph speed zones in Texas.

Seems to this feeble mind that all I am doing is adding additional cooling coils via the heater.

Thoughts????

 

[rottenronnie]

I'm experiencing déjà vu.

YES, that's exactly what is going on.

• Your heater core is acting as an additional radiator and removing heat when you turn it on.
• Your AC is adding additional heat to the cooling system and causing the temperature to rise when it is on.

Both perfectly normal.

 

[VIPR PWR]

I agree the fan blowing across the heater core adds to cooling of the engine but heats you up more lol. ...

The problem happening again at 80 mph ,,,, I’m not to sure about .. it would or should push more air through the radiator as speeds increase improving the cooling .. even in 100 degrees ... my thinking is either the setup restricts air flow through the radiator cooling fins some how at higher speeds .... all in all most modern autos tend to run in the 210 range anyway ... I don’t see it as a problem on the truck ...

Is there any damage to the radiator fins or the a/c condersor fins ?
I still think the underdrive pulleys are the wrong way to go on a street driven auto ... they slow down the accessories including the water pump .. which is possibly slowing the circulation of the coolant at the all speeds .

Thermostats can also cause a slower circulation of coolant if they don’t open fully.

Corrosion inside the cooling system slows down the circulation and can cause hot spots in the system ... Have you tried flushing the cooling system and does it have clean fresh antifreeze with the proper mixture of distilled water ?

 

[Silver05]

Air bubble ? Also doesn’t the fan have to be reprogrammed it tuned to turn on sooner ?

 

[CaptnCrash]

Some computer tuning doesn't manage the fans properly, been there done it. Of course the fans aren't really necessary at highway speeds.

Too much coolant in the system is also bad. More water less coolant is better. Be very careful with additives like water wetter. It doesn't play well with some formulations of coolant and makes jello.

In general under drive pulleys are bad for the street. In fact you should be using something more like 5% overdrive if the engine is built or heavily modified.

 

[Silver05]

When I was going to change my thermostat to a lower one , guys were telling me, the fan had to be tuned to turn on sooner, it would make no sense to install a 170 t stat and have the fans turn on @205, on my srt8 Jeep I installed a 180 and I tuned my fan to turn on at 195 178 and 185

 

[viperhauler]

Check your thermostat. It could be sticking.
My truck never sees over 200 and I’m blocking all my cooling system with a giant intercooler.

 

[Final GTS]

I dont see anything out of the ordinary here. A/C pumps heat in front of the radiator, heater core removes heat from the cooling system. Of course, you are going to see lower engine temps when the A/C is off and the heat is on.

Both A/C on and off have the same fan target temp, which is 200, so the only thing of consequence really changing is the additional heat added, or removed.

 

[Psycho1122]

I ran a stock thermostat on my 05' RC, underdrive pulley, 70% de-ionized h2O / 30% dexcool with water wetter. I also kept the grill block off panels for ALL the performance reasons. With Arizona temperatures, I had NO ISSUES with engine cooling. 190-200 degrees was consistent and normal. The stock Diesel radiator had MORE THAN enough volume and surface area to cool the engine. The underdrive pulley actually SLOWS down the flow through the radiator promoting heat transfer.

ALOT of misinformation within this thread drivers.

Cheers!