which will control overheating better? ive always thought the cooler the thermostat the cooler it will run, but ive heard the oppostie too. something about the coolant being in the rad longer with a slightly warmer one (such as 180 over 160) which would give the water more time to disperse heat. can somebody clear this up? thanks alot

Sure, I'll give you my take on that. Thermostats do serve another purpose besides just regulating when to open and close the valve, it also restricts the flow of the fluid allowing it more time to cool in the radiator instead of letting it circulate too fast without allowing it the proper time to have its heat dispersed in the radiator. It really depends on how hot you want your engine to run and also, the cooling capabilites of your setup. Say you want to run around 180-190 and your setup can keep the fluid cool at 170, no problem, just get a 180, maybe even a 190 therm. Whenever it hits that key temp, it will open up and allow the hot coolant to flow to the radiator to give it a chance to cool while at the same time, taking in the cool coolant that was in the radiator causing the therm to close. Your temp will rise about 5 degrees more than what the therm was intended for and then start to drop below that, closing it again until it once again, gets to that temp, opens up, lets cooler coolant in, hotter coolant out, again and again and again. If your setup is not great (like mine ) It will help to go to a higher therm like a 190 and let it cool down a little longer but if your setup won't keep it below that therm rating, it'll just stay open and won't cool as well BUTTT, it will help the coolant stay longer in the radiator since it does restrict the flow of the coolant as well. Even if your cooling setup does allow it to keep the temp down to an amazing 150 degrees, it would probably be better for you to have a 180 therm for a better operating temp since you don't want it to run too cool. Anyway, hope this helps you out and I apologize for those who don't want to read all this . Gl with whatever you choose.

If your cooling system is operating properly and sized correctly a 160 thermostat will maintain 160 and a 180 will maintain 180, period (within the deadband of the thermostat of course, which can be 5 degrees or so for a few seconds either side of setpoint). Simple as that.

To answer your question directly, run a 180, 160 is to cold. If you have cooling problems with that in there something else is wrong.

Basically what I said except muchhhhh shorter and not so freaken confusing lol. Do what he says if you don't feel like interpreting what I've said.

so a 180 would keep the coolant in the rad longer than a 160 (thus giving it more time to cool off) even if both thermostats are wide open?

A thermostat is not designed to keep the water in the radiator longer, its designed to keep the water in the block until it reaches a certain temp. Once that temp is reached, the thermostat opens slowly allowing the hot engine coolant to go to the radiator to be (hopefully) cooled down. Once the cooling system reaches the point where it cannot keep up with the engine temp, it will continue to rise. If it goes too high, it will over heat.
It is rare that any engine will run right at the advertised temp of the thermostat, unless you live where its cold year around. Usually, engines will fluxuate (sp?LOL) 30 or 40 or more degrees depending on load, outside temp and accessories that are being used like air conditioning.

Like was said previously, try a 180 and see how it goes. If it does in fact overheat and boil over, you have other problems.

If your car is a later model with any thermostatic vacuum switches, you will need to run a 195 to allow them to operate properly.

J-Mark has it right! Most of the newer stuff runs 195 to 205 thermostats. My 99 Z-71 came from the factory with a 205 in it and it runs at 210 degrees. They claim that running at the higher temp allows the engine to burn the fuel more effeciently.

The hotter engine is the more efficient engine because less energy of the combustion is given off as heat. But there's a happy medium, as in everything else. You don't want to be running at 160. 190 to 210 is safe and efficient. Anything over 220 and I would loook into troubleshooting the problem.

Just think about our internal combustion engines. When the spark ignites the mixture, there's an explosion. Energy is released in many forms: heat, expansion, sound. To minimize the use of one (heat in this case) is to maximize another, expansion/power/pressure.

The engine oil needs to be higher than 180 to burn off condensation. Thankfully, the oil is usually about 25 to 35 degrees warmer than the coolant, when everything is at operating temperature.

A quality thermostat, when working properly, will keep the engine at the rating..( plus or minus 5 degrees ).........IF the cooling system is in good condition and sufficient to cool the engine.........even here in the Southland ( over 100 degrees today ) My 32 ran right on the thermostat (180 ). A 180 degree thermostat is the General Motors recommendation for ZZ430 engines....

Nascar engine builders have proven that engine make more power at 200 degrees plus than at 160 degrees.

If you run a 160 thermostat and the engine runs over that......you have NO thermostat, in effect. The coolant is circulating back and forth between the engine and the radiator and does NOT have time enough in the radiator to cool down. A 180 would (could) change that. The coolant could stay in the radiator longer.

Most GM vehicles have had 195 degree thermostats from the factory for 20 years or more.

Auto manufactures spent millions designing cooling systems and a back yard rodder.... always TRIES to improve it....

__________________
Rat Rods are for those who cannot build a real Hotrod ...

Deuce hit the nail on the head with another topic that is touchy. A lot of people think that if they pull their car out of winter storage and run it until the coolant sensor reads 190 degrees, then that's good enough and they shut off the engine. Wrong! That's the worst possible thing you can do. The sludge and the condensation, as well as the acids don't have time to boil off in the oil because the oil is heated at a different rate and requires more load and time. That's why on a nice spring or winter day when you are storage, take the car out on the highway for some good driving to get all of the fluids at operating temperature.

Deuce, agree with 99% of what you said. A couple of variations I have read and heard at various seminars.

NASCAR runs at 200 or better due to restrictions of airflow not for increased power. If they could route additional air through the radiator, without increasing drag, they would. The most power is/can be made with the coolant cold and the oil hot. The major downside to this is increased wear to the bores.

Auto manufacturers have raised the setpoint on the thermostats for emissions purposes.

Auto manufacturers for sure spend tons of dollars on the cooling system design. They do the job they are intended to do. Stock pumps and radiators though can be replaced with aftermaket units to significantly improve the head capacity of the cooling system.

Italy's Finest, You'll have to help me understand how the Delta T between combustion at or above 2000 degrees is affected by a thermostat temp differential of 180, 190 or even 210. Remember as well that the total heat loss of the engine is not only to the water but also through the exhaust as well as the 33% that goes into moving the piston as useable work. Any power difference is going to be microscopic and usually is offset by an increase in intake air temp.

Nooo, that's not what I meant. I said you should go for a 180 (possibly higher) in order to have a better operating temp like some of these other guys are suggesting and a therm also slowwss down the flow of the fluid in the radiator, no matter which one you go with, giving it a little more time (not much) to cool off in the radiator. Whatever therm you choose, it'll do what Deuce is saying, fluctuate 5 degrees up and down from that particular rating which will be your operating temp, that is if your cooling system is up to date . Also, interesting info Deuce and Rick.

The temperature at the thermostat is relative. Do you think it's the same on the walls of the cylinders? I don't think so.

True........but who monitors it on a street car.....? I always try to install my sending unit as close to the thermostat. I have had one in the head and another in the intake as close to the thermostat as possible. Had them hooked to a rotary switch and checked them both....back to back.......the head was usually 10 to 15 degrees warmer....

The oil is warmer too than the coolant at the thermostat....but does run cooler with synthetic ....

And it is true that the NASCAR guys want their cars as aerodynamic as possible......but on short tracks they tear the noses off and look like a modified ( due to racing & rubbing ) and they still want the engine at 210 or better...

__________________
Rat Rods are for those who cannot build a real Hotrod ...

Thermostats have gone higher for better emissions control to a degree, but less emissions usually means the charge is being burned more efficiently, so six of one/half dozen of the other IMHO.

Ramblers have used 190-195 degree thermostats since the 1950s, when everyone else was using 180 degree. Fuel efficiency was one of the reasons, made for one heck of a great heater too!

A hotter thermostat does let the engine get up to operating temp faster. I'ts not uncommon for today's engines to run at 250 degrees on a hot day under load, even 260 in the worst conditions. Many new cars aren't considered to be running hot until they go over 280. This is usually with a 16 pound pressure cap.

The cap is often over looked in overheating situations. If it won't hold the rated pressure the system will boil over. Another thing -- the higher the pressure, the more heat the system will take before boiling over. I wouldn't go slapping a 16# cap on a system designed for a 7# cap (were the old systems 6# or 8#? been so long I forget... maybe 5#?) without checking everything else first, but if you have a newer replacement radiator it should be up to 13# of pressure. The extra pressure will make a tremendous difference! I run a 16# cap on my Rambler (has a 1987 Jeep 4.0L in it) with the original radiator. The radiator has been recored though, but everything takes the extra pressure with no problems (originally had a 5-7# cap). The original engine had a 195 degree thermostat like the 4.0L, but the engine sure does like the extra pressure much better! Runs around 210-230 degrees even on the hottest days with AC running.