View Full Version : Thermostats

05-20-03, 12:05 PM
Seems to be a lot of confusion about exactly what the thermostat does.

The basics: the thermostat is a temperature-controlled valve that keeps the coolant from leaving the engine block when the coolant is below a certain temperature. When the coolant goes above that temperature, the termostat diverts it out to the radiator.

In operation, the termostat regulates warm-up, and sets the lowest operating temperature of the engine. It goes something like this:

*Start the engine.
*The coolant is forced to remain circulating in the block.
*Heat from combustion heats the coolant quickly.
*Soon, the coolant reaches the thermostat temperature, and the thermostat diverts it to the radiator.
*Now, the coolant is transferring heat to the air and losing temperature.
*If the radiator is efficient enough (say, a really cold day), the coolant may drop below the thermostat temperature, which causes the thermostat to limit it to flow inside the block again, until it warms up.

What it all means is that the lower the thermostat temperature, the longer it takes the engine to warm up (since it only gets an "assist" until the termostat temp - after that it has to fight the radiator to warm itself), and the lower the engine might go, if conditions permit.

What it also means is that lowering the thermostat has no affect on the upper temperature limit.

Now, some people may not care about a quick warm-up, but remember that you shouldn't start pushing the car hard until it is warm, so a long warm-up means delayed fun. More importantly, though, is the limit the thermostat places on the minimum operating temperature. Too hot is bad for you engine. But so is too cold. Dropping in an extremely low-temp thermostat can allow your engine to run colder than it should, increasing wear and leading to a shorter life.

So, what's a 'Vette-lover to do?

Well, I'd say that we should take a lesson from the General. Current tehrmostats are generally 195. This makes the engine run a little bit hotter, which lowers emissions. Pre-emissions, the thermostat temp was 180.

If emissions is not a big worry, I'd say that 180 is best. That keeps the engine from getting too cold, warms it up quick enough, and won't push it hotter than it needs to be, either.

I can't think of any time when a 160-degree thermostat came from the factory, and I can't imagine why anyone would want a street car to run that cold, since the engine wear would be increased dramatically, warm-up would take longer, and any gain in performance due to lower operating temp would be small, when compared to the shorter performance life of the engine.


05-20-03, 12:46 PM

05-20-03, 12:55 PM
good points in there,but i disagree about engine wear.with a 160*t-stat my oil would still reach 195 to 200*,and with pure synthetic oils out there,i just cant see the wear,i can see extra carbon build up to decrease plug life,thats ok to me,make sure you decarbonize about every year.anyway have a good day,Todd.

05-20-03, 05:44 PM
Although it takes a long time, our carefully-documented and controlled OEM testing at both GM and Chrysler showed very clearly that the rate of bore and ring wear at 160* engine temperature was double the wear rate at 180*. One of the reasons for the move up to 195* thermostats was reduced bore and ring wear, for reduced hydrocarbon emissions and reduced blow-by contaminants. A 160* thermostat usually won't allow sump oil temperatures to get high enough to boil off moisture condensate and blow-by contaminants, which dramatically accelerates the formation of acidic sludge; this doesn't mean much in a race engine, but it means a lot for long-term reliability, durability, and emission system operation (50,000-mile emission system warranty) in a normal street engine.

BTW, good post on thermostat operation - most people don't understand that thermostats only control the MINIMUM operating temperature (where the cooling system is efficient enough to cool to that level), and have nothing to do with the maximum operating temperature.

160* thermostats were specified back in the 30's, in the days of alcohol-based anti-freezes, which would boil off at engine temperatures of 185* or more.