Tech Tips
Cooling System Mods

Because GM theorized that a car operating at higher temps would render more efficient emissions and more complete combustion burn off, they blessed us with a car that has a stock 195° thermostat and fans that don't turn on until 234°. Guess what.......that's way too hot, and while their emissions scenario does hold water, at what expense? Robbed power, overheating cars, and increased engine wear.

First Step in an overheating car is to inspect the air dam assembly underneath the front of the car. If you have air dam damage you will experience a strange overheating problem. As you drive the car on the highway it will gradually overheat and go redline. In most normal autos when you hit highway speed increased airflow will cool things off. With the Trans Am, we have no grille. 80% of the cooling comes from underneath the car. The critical piece is the plastic piece that attaches to the radiator and diverts airflow into the radiator. This is called a Center Air Panel Deflector, GM P/N 10020322, $ 29.14. This piece is critical for proper airflow, as is the spoiler strip that attaches to it and runs the width of the car called Radiator Lower Air Deflector, GM P/N 10017673, $ 23.05. If these are damaged, as they frequently are on curbs, speed bumps, etc., don't think their repair can wait.

Second Step would be to install a lower degree thermostat. Many enthusiasts, magazines, and manufacturers suggest a 160° thermostat. There is evidence that the 160° stat is too cold for these engines, aside from the fact that your heater and defrost will be much less effective, should you need them. With this in mind, in the past, there are many that utilized a "winter" and "summer" thermostats being a 180° and 160° respectively. But a few diehards through research discovered that even though GM doesn't list it in their application charts there is an AC Delco 170° thermostat available through any GM Dealer by ordering part number 10220957. There are some pricey ones through after market suppliers also.

When you get the thermostat drill 4 small holes in the body to allow a minimal constant flow. This will prevent "hot pockets" from building in your engine block and will help eliminate air from the cooling system.

Third Step
would be to install an adjustable fan relay. I used an awesome unit from Derale. Part # DER-16759 $ 39.75, from Summit Racing. It comes preset at 170° but may be adjusted by a wide range ±. It also has provisions for dual fan units. Article on Derale Adjustable Fan Switch.

By following these 3 steps to a cooler engine you will reap the benefits of the horsepower that cooler temps bring, without sacrificing the use of your heater or defrost, or the hassle of changing thermostats twice a year.

Along with your new mods you should check timing, fuel system operation, O2 sensor, to eliminate any "lean" conditions which will also contribute to overheating. Double check and/or flush radiator and provide the proper water/anti-freeze mixture. Do Not run pure anti-freeze, use just enough A/F to protect to your lowest anticipated temp, plus a few degrees. For lack of a statistical calculator to figure this just go 50/50. Check for damaged fins and leaves, paper, and other obstructions that could block airflow. Check lower hoses for soft feel which could cause hose collapsing under pressure.

If you have severe conditions (as I do: 120° temps, mid day traffic, A/C on, here in the Phoenix summers) and you have the single cooling fan, you can do a dual fan conversion with GM parts for about $ 275.00. I will cover this in more detail in another article.

Your new adjustable fan relay can be wired in conjunction with the original GM configuration to give you a switchable setup that would allow you to revert to stock at the flip of a switch for emission testing.

Third Generation member "
Willie" has a very informative article about GM Cooling Systems that everyone should read and Third Gen member "Desert86Roc" offers an informative article on Dual Fan Conversion for single fan cars.

I am coming to the conclusion that this would be the best guideline I could offer for which thermostat to use:
195° ~ If you live in the Artic Circle
180° ~ If you live in a predominantly cool climate.
170° ~ If you live in a predominantly warm climate.
160° ~ If you live in a hot climate.

Related Articles:

Overheating Car
A/C Sealing Strips
Thermostatic Theories

Derale Fan Switch Install
Single Fan Schematic
Coolant Temp Sensor 


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