Should I replace the thermostat?

I am going to drain the radiator and put in new coolant and fluids. I was just wondering, Should I replace the thermostat also? And why? Also what are the differences in the thermostats? I see that alot of people say they have a 180* thermostat? Why do most people seem to choose that one? I am really just looking for any advice. Thanks.

Also If someone has a "how to" on draining the coolant that would be very helpful. I read in my manual that I can pull out sensors on the block. I thought it was just the radiator? But I guess not.

Unless you are having problems with the cooling system like overheating it is not necessary to replace the thermostat. However, if you have any doubts about it then replace it. Thermostats are either 195 (stock), 180 or 160 degrees. The 180 is a good all around thermostat and will not trigger a ECT error code while the engine is warming up to operating temperature whereas a 160 may without a reprogramed PCM module. GM recommends the 195 due to emissions control. For L67 GTPs a lower temp. thermostat may help keep the engine cooler and reduce knock retard.

What thermostat to use depends on where you live and the climate. You would not want a 160 degree thermostat up North in the winter. A 180 should be OK but the heater may not feel as warm until the engine gets up to full operating temperature.

I would not mess with the two engine drain plugs. Too hard to get to for a routine cooling system flush.


For a suggested general cooling system flush procedure click on View Answer.


Use Prestone Super Flush which is an additive you pour into the cooling system before doing the actual flush. For antifreeze/coolant I use Prestone Extended Life. It is in a yellow container and will appear green in color.

Here is a basic coolant flush procedure:

Install the flush T from the Prestone Flush Kit in the heater return line hose.

1. With engine cool, remove radiator cap and drain the radiator.
a. Turn drain plug (lower left engine-side of radiator) counter clockwise about 1/8 of a turn (may require a little force if it's not been opened in awhile--be careful because it's plastic). Use the end of a 1/4" drive handle. Plug will extend slightly as it loosens. Be sure to have a container in-place to collect the antifreeze.
2. Let all the antifreeze drain into a container.
3. Remove, drain and clean the antifreeze overflow bottle. Reinstall bottle.
4. Hook up a garden hose to the flush T and turn water on (not too high or you can damage seals/gaskets with the pressure). When water starts to run from the drain plug, start the engine and turn the heater on (make sure you leave the water running during this process).
5. When water runs clear (about 5 - 10 minutes), turn off car, then turn off water, and remove hose from T and cap it. Let remaining water run from drain plug. (Note: Not all of water will be drained out of system mainly the engine block. What I do is hook up a drain hose to the T connector, start engine and let the water pump push water out of the system. As soon as you see no water coming out turn engine off, remove drain hose and cap off T connector).
6. Close radiator drain plug and fill radiator with a 50-50 mix of antifreeze/distilled water (or buy premixed).
7. Start vehicle and bring to operating temperature to make sure thermostat opens. Add additional mixture as necessary until full.
8. Reinstall radiator cap.
9. Release any trapped air in cooling system by turning the plug on the top of the thermostat housing (be careful not to burn yourself). When only coolant (no air) flows from the plug, close it. You may have to repeat this several times to get all of the trapped air. Raising the front end of the car where the radiator is higher than the engine helps bleeding.
10. Add additional coolant as necessary. Also, fill overflow bottle to recommended level. Be careful not to open radiator cap if hot. You may have to do this several times.
11. Check for leaks.
12. Properly dispose of old antifreeze.

Well I have recently been losing coolant from somewhere. I am not sure where though. I filled up the cooling system about a 1 1/2 weeks ago and I had to put 2 gallons in today. When I start the car and look for water I cannot find any dripping from anywhere.

I'll probably go with the 180 then. I live in Phoenix, AZ so It is always hot. our low in the winter time is about high 40's. So I am sure that one will be fine. Can I get them at any auto parts store like Checker/pep boys/auto zone???

I will just drain from the radiator then. I really didnt want to mess with the block.

If you are losing coolant internally, you probably have a bad intake manifold and/or intake manifold gasket.

If you are losing coolant internally, you probably have a bad intake manifold and/or intake manifold gasket.

If that is the case, Woulnt I see water coming from the block and the gasket area.?

Not necessarily. If you have a SE/GT with the NA SII 3800 then the UIM and LIM gaskets can go bad causing internal coolant consumption where it is burned in combustion. Also, a bad throttle body gasket can cause a similar problem.

For now do a cooling system flush and cooling system replenishment as per the procedure provided. Sometimes a flaky thermostat will give erroneous coolant level readings leading you to believe there is coolant loss. I would replace it to be sure but try to stay with an AC Delco brand versus the aftermarkets like Stant. After that monitor coolant usage. If still consuming coolant then the intake gaskets would be suspect. Good luck.

Change your thermostat! When coolant level runs low the thermostat is no longer surounded by water, causing the thermostat to become overheated and damaged usually causing it to stick open unnoticed. Eventually the disc and actuator pin will slip again and the thermostat will stick closed unable to open.

Fix your coolant leak first.

Draining and refilling your cooling system will not neutralize the acid that builds up in every cooling system. $3 fast flush will do that, it isn't about unplugging restrictions. Acidic coolant will cause LIM leaks sooner than if the coolant is maintained. If you flush your cooling system there will only be clean water in the block.

There is no need to re-engineer the standard of the automotive industry by useing a t-stat other than 195. So many engineers conducting extensive testing have determined that 195 is the best temp for efficient combustion; EEC, motor oil, and the engine, are built around 195 operating temp. You can't change the temp of your fans. Your engine is going to run 210 regardless of your choice of thermostat temp, when every t-stat will be wide open.

If lower temp thermostats are not a benefit in Phoenix, where in the world are they a benefit? Just an emissions thing? Hardly the case!

Lower temp thermostats will not extend engine life. Engines with coolant leaks regardless of T-stat will have shorter life.

I have to agree with the fleet rep engineer from GM visiting in Phoenix while conducting training, "One thing that is certain, There is no such thing as a regional thermostat."

Hot climate testing is conducted by several auto manufactures in Arizona. GM can't afford to mow the weeds let alone maintain their test track surface. They have determined that driving between East Mesa and Flagstaff on roads maintained with federal funds makes a lot more sense with more realistic conditions. The most severe test conditions on any engine and cooling system has to be the 20,000lb loaded UPS trucks powered by a 4.3 GM that race stop and go all day long under Phoenix temperature conditions. They all use 195 degree thermostats and are changed every year. They do not have overheat problems.

Are you assuming that "most people' have 180 degree t-stats. They do not. 180 just seems like a better idea to a lot of people whom continue to recommend to others without solid reasoning or support that could justify any benefit.

There is no need to re-engineer the standard of the automotive industry by useing a t-stat other than 195. So many engineers conducting extensive testing have determined that 195 is the best temp for efficient combustion; EEC, motor oil, and the engine, are built around 195 operating temp. You can't change the temp of your fans. Your engine is going to run 210 regardless of your choice of thermostat temp, when every t-stat will be wide open.

Oh really?? I don't know about that but I disagree. Grand Prix owners re-engineer and/or modify their cars in the quest of more performance every day in this country. I use a 160 degree drilled thermostat in my GTP with no problems and I'm in the Southwest. I have a re-programmed PCM module with fan turn on point at 185 degrees. My temperature has never exceeded 180 - 190 degrees. Your statement regarding the engine running at 210 is either erroneous or not applicable depending on the poster's circumstances or as general advice to a wide audience in this forum. I seriously doubt I am getting less than satisfactory efficient combustion as proven by Autotap diagnostics and my 1/4 mile ETs. Also, it passes Texas emissions testing every year.

I recall this member may have a re-programmed PCM module, therefore not stock either.

A re-programmed PCM from DHP, ZZP or Intense basically does the following and highly recommended if you live in hot climates which will also allow using less than a 195 degree thermostat.

* Speed limiter removed
* Raised rev limiter
* Raised shift points
* 3-1 and 4-2 skip shifts
* Transmission line pressure increased
* 185F fan turn on
* 90 second fan on at key-off (this feature activates when engine coolant is 180 degrees or greater)
* MAF calibration is year specific
* WOT fueling richen to reduce KR
* Removes lag by changing downshift tables
* Correct VIN number programmed in
* Part throttle KR issue fixed
* Torque abuse modes are modified to eliminate bog at launch
* Shift KR is remapped for modified vehicles
* Power enrichment tables modified for cars running increased boost
* P0128 code removed for running drilled or 160 Tstats on newer cars
* Torque converter lockup tables modified to improve transmission life and eliminate ‘converter lockup hunting’


The most severe test conditions on any engine and cooling system has to be the 20,000lb loaded UPS trucks powered by a 4.3 GM that race stop and go all day long under Phoenix temperature conditions. They all use 195 degree thermostats and are changed every year. They do not have overheat problems.

What does a UPS truck test have to do with a Grand Prix? If you are going to put possibly bogus and irrelevant tests in a post then be prepared to take criticism and have it deemed as a non-contributory post. IMO the most severe test is a modified GTP running at the drag strip.

BTW - What year and model Grand Prix do you own?

Are you assuming that "most people' have 180 degree t-stats. They do not. 180 just seems like a better idea to a lot of people whom continue to recommend to others without solid reasoning or support that could justify any benefit.


Yes I am just assuming that "most people" have 180 degree t-stats. I have looked at several peoples GP's on forums and thats what most people have.

I recall this member may have a re-programmed PCM module, therefore not stock either.




And Yes I do have a re-programmed PCM from ZZP. just to clarify.

Yes I am just assuming that "most people" have 180 degree t-stats. I have looked at several peoples GP's on forums and thats what most people have.

Then that is a valid assumption. The 180 is the most popular thermostat of GT owners. 160 for GTP due to the supercharger and running higher than stock boost. This helps control knock retard a few degrees by letting the engine run cooler. And I know for a fact it does.

And Yes I do have a re-programmed PCM from ZZP. just to clarify.

Thats what I thought. It stuck in my mind because you had referred to it as a chip. :lol:

Then the 180 TS with a fan turn on point of 185 degrees programmed into the DHP PCM will be ideal.

If your decision is to use the 180 then go for it. :thumbsup:

Thats what I am going to do. Thanks for all the advice you have given me soooooooooooooo many times

Yes my information is for most people as were referred to in the post. No need to become so defensive. I am very much aware of what a lot of people think about thermostates and able to accept critisism. Maybe you guys refer to most people as being those individuals on the forums you read. Counting a limited group of people does not provide accurate measurement, constitute a majority, or have any effect on the validity of their words. Do you think your engine performance would suffer if air intake temps were the same, and your engine temp were 195-210 rather than 185? I am interested in learning why you might loose HP in any range. I am not suggesting that your combustion is less than satisfactory. If you believe it to be optimum, you would not continue tuning. The information I share about thermostats and cooling systems is accurate for every automotive thermostat in every vehicle. Benefit from my contribution or wait until after you have a problem. I suspect you do see the relavance of testing and performance. Every vehicle has a cooling system. The example I used is accurate for on road vehicles and basic fundementals deffinatly carry over to performance situations. From what you report that you know about you car's reprogramming, you must agree that high coolant opperating temp in vehicles is ultimatly controlled by air flow through the radiator rather than by an open T-stat. I can agree that your cooling system is tested at the track under more severe conditions, and yet does not begin to compare with many other high performance situations. Do you know who manufactures the thermostats that go into an AC Delco box? What A/F is to me, is the many opportunities provided for me to learn each day, as well as teach, and there is often the entertainment factor. I would never have guessed that jbizels water injection experiment, and adding 2 gallons of coolant at one time in less than two weeks was in some way connected with someone whom is seeking to improve performance.

One good way of flushing a cooling system is to drain the coolant, remove the t-stat and replace the same housing. Then remove the upper radiator hose from the radiator. Add water to the radator so that a trickle of water continues to pour from the radiator while you run the engine at idle. After the water is flowing clean put the hose back on and add the fast flush to neutralize the system. After running the recommended amount of time of the fast flush instructions, remove the radiator hose and flush again. Then put a new t-stat of your choice in and add anti-freeze to reach a 50/50 mix.

Careful JustSayGo. :nono:

This not a general automotive forum. It is a forum dealing with Grand Prixs and it is my job as one of the forum Moderators and leaders of the forum to ensure information is relevant to the issue at hand and specifcally addressed to the needs of Grand Prix members. We have other areas like Engineering/Technical and Cars in General to share general knowledge you can post in, however, based on your responses it would be open to debate there too.

You failed to answer my question about year and model Grand Prix you own so therefore we must assume nada which says alot about your ill-advice.

BTW - It was undertermined as to whether he actually has a coolant loss. He could have been shortchanged on the prior cooling system service or it was not checked properly at the radiator. I'm quite sure he did not want to hear he may be looking at a UIM/LIM job before pursuing other inexpensive and reasonable courses af action. Never assume in this forum as you have. You did not realize he had a reprogrammed PCM module which changes the equation and your so called theory about thermostats. The issue was he wanted to use a 180 degree thermostat and received the proper response based on his specific situation.

Also, your cooling system service leaves alot to be desired. He was provided with the proper and proven procedure we all use at Post #2 at the "View Answer" button. Open your mind and maybe you will learn from us. And yes, you were very entertaining and downright laughable. In the future, if I see any of your posts as non-contributory they will either be deleted or sent to our spam file. This thread is closed!

Use Prestone Super Flush which is an additive you pour into the cooling system before doing the actual flush. For antifreeze/coolant I use Prestone Extended Life. It is in a yellow container and will appear green in color.

Here is a basic coolant flush procedure:

Install the flush T from the Prestone Flush Kit in the heater return line hose.

1. With engine cool, remove radiator cap and drain the radiator.
a. Turn drain plug (lower left engine-side of radiator) counter clockwise about 1/8 of a turn (may require a little force if it's not been opened in awhile--be careful because it's plastic). Use the end of a 1/4" drive handle. Plug will extend slightly as it loosens. Be sure to have a container in-place to collect the antifreeze.
2. Let all the antifreeze drain into a container.
3. Remove, drain and clean the antifreeze overflow bottle. Reinstall bottle.
4. Hook up a garden hose to the flush T and turn water on (not too high or you can damage seals/gaskets with the pressure). When water starts to run from the drain plug, start the engine and turn the heater on (make sure you leave the water running during this process).
5. When water runs clear (about 5 - 10 minutes), turn off car, then turn off water, and remove hose from T and cap it. Let remaining water run from drain plug. (Note: Not all of water will be drained out of system mainly the engine block. What I do is hook up a drain hose to the T connector, start engine and let the water pump push water out of the system. As soon as you see no water coming out turn engine off, remove drain hose and cap off T connector).
6. Close radiator drain plug and fill radiator with a 50-50 mix of antifreeze/distilled water (or buy premixed).
7. Start vehicle and bring to operating temperature to make sure thermostat opens. Add additional mixture as necessary until full.
8. Reinstall radiator cap.
9. Release any trapped air in cooling system by turning the plug on the top of the thermostat housing (be careful not to burn yourself). When only coolant (no air) flows from the plug, close it. You may have to repeat this several times to get all of the trapped air. Raising the front end of the car where the radiator is higher than the engine helps bleeding.
10. Add additional coolant as necessary. Also, fill overflow bottle to recommended level. Be careful not to open radiator cap if hot. You may have to do this several times.
11. Check for leaks.
12. Properly dispose of old antifreeze.