Tech Tips
Thermostat Theories
82 - 92 F Body Series

 

There seems to be much discussion about:

Which thermostat do I use?
Will running my fans all the time hurt anything?
What is normal operating temp?
I put in a 160° thermostat and my car still overheats.

 
I have some theories that may put some of these issues to rest and help us all understand how our cooling systems work and bring some "myths" to light.
 
The Basic Theory - of cooling operations regarding thermostats is as follows. With the radiator, engine block, and overflow tank we have app. 17.2 quarts of a 50/50 mixture of antifreeze and water to cool our engines. A few quarts reside in the engine block the rest outside the engine. A thermostat, by closing, separates these two circulation areas whereas the block will heat it's own water first until it reaches the thermostat opening temperature. Then the stat will open thereby increasing the volume of coolant that is being circulated by the water pump. This "dual" system allows us to reach operating temps faster to heat the oil, fluids, and to render the interior heater usuable in a quicker timeframe.
 
The Stock Thermostat - in our cars is a 195° thermostat. This is by GM design (although a poor one) as GM decided the cheapest way to reduce emissions to meet EPA standards was to increase the heat range our cars operate in. Good for them - bad for us. For us this results in a loss of power, overheating cars, and increased wear to our engines, not counting our nerves.
 
Normal Operating Temp - on our cars is in fact 195°. Every calibration in the GM tech manual that calls for normal temp at 1000 RPM idle is set to 90° C which converted is 194° F. Exactly why we have a 195° thermostat.
 
Thermostat Myth - Many assume a 195° thermostat is open at 195°. This is not correct. This is when the thermostat is calibrated to "begin" to open. It will be totally open at approximately 206° and close at 188° in order to try and maintain a 195° "middle of the road" temp. This is known as the operating range.
 
Ideal Situation - would be for our engines to be cooled totally by the opening and closing of the thermostat. But when this doesn't happen because of increased load (towing, A/C use), underhood mods, or an intense environment our cooling fan kicks in at 234°.
 
Cooling Fans - on an electric fanned car should not be considered "normal operation". As I said the "ideal" would be totally controlled by the thermostat. Our cooling fan is our "danger zone" or "early warning" or "last resort" or "safety measure". Our fan is saying "your engine is about to overheat I'm going to cool it down for you". Please keep in mind, before anyone gets in a great debate on this issue with me the purpose of this bold and brash statement is to later explain why some cooling mods don't work. Of course our cooling fans ARE a part of our "normal operation" because we DON'T live in an ideal world....... see where I'm going with this?
 
Be Sure - that if your car is running 260° - don't think that since your fans don't even come on until 234° that you are OK. Antifreeze will boil at 262° at sea level with 15 PSI radiator pressure. You are about to cook something. That is what I mean, your fans kick on at a very late stage.....almost too late.
 
Running the Fans - all of the time is not a great crime. Yes your warmup time will be slightly increase...... big deal. A belt driven fan runs all the time. What will be the most affected is that your electric fan motor is good for X number of hours. By design your fans don't run all the time. In some situations they are OFF most of the time. So running the fans all the time will consume your X number of hours of fan life at a more rapid rate. If you can live with that then there is really no problem......unless of course that last hour of life is in the middle of the Arizona desert 100 miles from nowhere.
 
Environmental Theory - A 195° thermostatically controlled engine will act differently in Phoenix, Arizona on a 120° day in rush hour traffic, with the A/C on, than say a cold blistery day up North somewhere. In traffic driving will have a different effect than a highway cruise. A/C On vs. A/C Off. Underhood modifications which increase horsepower usually also increase the heat for example headers. Which leads us to the conclusion that the 195° stock thermostat is a "one size fits all". One part - every car. This is where the problems begin and the misunderstandings start. This is why a 160 works better for one person while another gets better results with a 180. But for all practical purposes most owners I have encountered agree - "We have to lower operating temps".
 
Temperature Momentum - is the last theory I have before getting down to solutions. If you point an airplane nose down at 200 MPH and pull the nose up right before you hit the ground - you will still smash into the ground - belly up. If your boat is headed to shore at 50MPH and you make a sharp left turn, right before the shore, you're still going to hit the shore - you'll just do it pointing left. AND if your temperature has an upward momentum, especially due to abnormal conditions, it is going to peak REGARDLESS of what thermostat you have installed. This is a very important theory to answer questions like "I put in a 160° thermostat and my car still overheats" or someone who says "160 is too cold, your car won't run right"...... not necessarily true.
 
Which is Why - there is such a great debate on which stat is right for you. The installation of a lower thermostat and an adjustable fan switch that lowers the temps that your fans come on is an "attempt" to lower the operating range of your car. Just because you put in a 160° stat doesn't mean your car will operate at 160°, but what's important is that it will try to. It will "attack" a temperature momentum rise at an earlier stage and in many cases that is enough to solve serious overheating problems. Temperature Momentum at it's late stage is sometimes impossible to overcome. It just has "too much" momentum, and dealing with it early or before it happens is the key to success. And this is exactly why a 160° thermostat may be too cold for the rest of the world but it may be just right for you. There are those that recommend a 160° for summer and a 180° for winter which is why I run a 170° year round.
 
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 "hotter than hell" climate.
 

Acceptable operating temps are the result of:

1. The tuning of your engine.
2. Your driving habits.
3. The increased loads you have implemented. (towing, A/C, headers, etc.)
4. The thermostatic and fan turn on temps you have selected.

 

What do we do?

 
You may be here because you have:
1. Added mods or increased the strain on your cars cooling system.
2. Gone through the basic troubleshooting of your cooling system and still overheat.
3. Are just generally concerned about your cars operating temp.
4. Live in a harsh temperature environment whereas the stock system just doesn't cut it.
 
Overheating Car
Lower Operating Temps ~ Cooling System Mods
 

Related Articles:

A/C Sealing Strips
Derale Fan Switch Install
Single Fan Schematic
GM Cooling Systems
Coolant Temp Sensor 
Cooling System Mods
Dual Fan Conversion


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