mojo1

If a thermostat is stuck open it will cause the "bubbling". The thermostat opens and closes giving your coolant time to cool off in the radiator. When stuck open the coolant will keep circulating and just get hotter and hotter until overheating occurs. You should change it right away. I hope this will help you.

TEXHAWK0

Antifreeze not only lowers the freezing point, it RAISES the boiling point. Without antifreeze, the boiling point would be at 212 deg. F, with antifreeze, I think it raises the boiling point to up around 265 deg. F. at 15 psig.
You might want to check to make sure you have at least a 50/50 Dexcool/water mixture. If the radiator cap is not holding the right pressure on the system, it can also cause boiling at a lower temperature.
Why haven't you already changed the reservoir cap just to eliminate that as a possibility?

The thermostat change is simple. I would let the engine cool down before working on it. Then it is just removing the two bolts that hold the thermostat housing in place, and removing and replacing the thermostat. Reinstall the two housing bolts. Refill with coolant.

ptindall

Yes the cap could be the problem. The system needs to pressurize to work. There may not be a write up because it's too easy for one. "Open hood, replace thermostat, close hood" It's in that little housing below the belt tensioner. Just remove the two 8mm headed bolts and swap it out. You may not even have to disconnect the radiator hose from the housing if you don't want to. Just make sure you put the new one in the correct direction and refill the coolant as you will loose some. You can test your old thermostat by putting it in a pot in the stove. Cold, it should be closed. Turn the stove on and when the water hits 190, you should see the inside part start to open up. As the water gets to boiling, it should be wide open. It is possible for them to fail at any time.

97C5driver

well because i just seent the suggestion of the cap this morning. so i have someone picking up the cap for me right now. I will try that and i ordered the t-stat which will be in tomorrow morning. How many gallons of dex cool will i need after changing the t-stat?

I went up the street just now to get some oil and p/s fluid and the car never passed 210 degrees but sure enough was spitting out coolant when i came to a stop at my house.

im just praying that it is not a head gasket or warped head because my warranty just ran out!!!

TEXHAWK0

You should not need more than a gallon of Dexcool to replace the coolant lost when you change the thermostat. I would still check the mixture to make sure you have at least 50/50. If you do not have a coolant tester, it would not hurt to drain as much coolant out as you can (probably about 2 gallons), and mix up 2 gallons of 50/50 Dexcool and distilled water. If you put at least 2 gallons of 50/50 mix back in the system, it should not be too far off. ( the total cooling system capacity is about 3 gallons)

ptindall

When it is cold outside, this cycling happens, and when you first start the car this cycling happens, but when you are driving around in 110 degrees for hours you better believe the thermostat is not closing. The coolant on the engine side has to get down to like 180 for the thermostat to close. That means you would have to see 180 or less on your gauge as the coolant has been in contact with the engine longer when it gets to the thermostat than your gauge sensor. That does not happen. Same thing when racing. Let's say your temp is hanging around 200 while racing. The thermostat does not have a computer in it to tell it to close. The coolant contacting the thermostat will never be cold enouph to make it close. Any yet, it does not get hotter and hotter and overheat. If this cylcing was ALWAYS happening, you would see your coolant temp constantly rising and falling on your gauge. But you don't, do you?

97C5driver

Well i put a new resovoir cap on, drove about 10 minutes, temp got to about 220 max. stopped at my office and there was no coolant spewing out of the tank like before but there was small amounts trying to escape out of the small hose that connects to the top of the resovoir right above the cap.

So the hose was leaking out a little coolant and making some noise.

So there is obviously still some sort of problem. Any diff. ideas now after this ???


Thanks.

ptindall

You might just be low on coolant now, but I'd still put in the new thermostat ASAP and test the old one and go from there.

04cad

Did you mean to say a new "radiator" cap? The reservoir cap wouldn't probably affect this problem much. You did say you checked under the front of the car where the air intake for the radiator is and it was clear, correct? Also be very careful with the thermostat bolts, I am not clear if they are screwed into aluminum or not on these cars, but if they are, they very well may snap off when being removed, due to the steel galling to the aluminum. Hope you get this figured out soon.

Cole

KISS - Check the radiator cap then the fluid when you have the cap off. Then the thermostat. Run the system cold with cap off and await the theromstat opening - you can see the flow change when it opens.

ptindall

Like most all modern cars, the C5's resevoir is a connected part of the cooling system. The resevior is pressurized with the system. so the resevoir cap must seal. I think you are thinking about an old overflow tank. The C5 does not even have a separate radiator cap. (90% sure about the lack of rad cap) (100% sure about the rest) The bolts do go into aluminum, but I betcha $1000 they come out just fine.

97C5driver

well the cap definately reduced the spewing of coolant. i put a proper level of coolant/water in the tank before putting the new cap on.

so when the coolant tries to escape now its through the hose on the resovoir and it bubbles up and makes a hissing noise.

this cooling system stuff is some weird crap.

So I will have the new t-stat on tomorrow, along with a new resovoir tank (because my sensor is bad on mine), and some fresh dex cool/clean water.

im still confused as to why the cap would reduce the spewing, but the coolant is still trying to escape through the hose.

TEXHAWK0

Did you check the coolant to determine if you had at least a 50/50 mixture? If the boiling point is too low, you could still be trying to create steam at 220 deg or less.

One reason the coolant may still be trying to escape through the small return hose is the cheap clamps they put on at the factory. If it is still one of the spring type clamps, the clamp may have lost some of its clamping force. You might try replacing the clamp with a new factory type, or just go to a small screw type clamp.
The hose may also have lost some resiliency and cannot form a good seal.
When you buy GM replacement hoses, you also get new clamps.
OR...check the fitting on the tank that the hose slides onto. It may have developed a crack. If it is seeping at the fitting on the tank, the new reservoir should fix that.

97C5driver

good point ^^^^. i'll get a new hose as well with a screw type clamp. i didn't even mess with the mixture ratios yet. i figured i would deal with that tomorrow when i swap out the resovoir and t-stat.

thanks to everyone for their help on this situation. it's been a great relief having some support here......

UKXPAT

Sorry that you have this problem but this is THE BEST resource that you could have! There are so many cool people on here with expert knowledge who are willing to share it!

I'm sure that you'll get it sorted out with the help of these guys

ptdrummer54

I want to see the answer to the questions on whether or not the fan was working? I know you're replacing the tank due to a sensor failure, is that what is supposed to control the fan? If you turn on the AC it will force the fan on, so you could at least verify that it works. I would assume the fan should be coming on at or before 220, but I don't know what triggers it.

97C5driver

well i can hear it on when i turn the a/c on but i don't think they come on up to 220 degrees. I cant see the fans or really determine if they working.

At what temp. are they supposed to turn on? (assuming they are at the stock settings)

mojo1

point taken , thanks.I am not an engineer , just a goober.

BLOWNBLUEZ06

If I'm not mistaken, my fans come on at around 180. They may have changed the factory programmed temp when they put the motor and supercharger in and tuned it. You don't have to listen for fans if you're careful, you can reach your hand behind the fans and check for airflow. It seems that you have an airflow problem though, because you seem to be fine until you stop and that is where it is the fan's responsibility to move air across your radiator and condensor. If you were overheating while driving too, I would have a greater suspicion of the thermostat. It is very easy to replace, so you might as well replace it, but don't get too disappointed if you have more investigating and work to do.
I haven't read that anyone mentioned that you should not put tap water in your cooling system. Filtered water may work but the absolute best and proper thing to put in is distilled water and I would not put any other type of water in. Distilled water has all of the minerals removed. The minerals will stick to everything in your cooling system and before you know it you will have your own personal coral reef inside which will cause overheating. After you install the thermostat, monitor your temps while driving on the highway, then cruising and then at idle. If you are only having this problem when at a stand still and your coolant level is full, then reach down behind the fans and make sure air is moving through both of them. If not, time to focus on that. If you find that air is not moving through both fans, let us know and we'll try and help you work through it.

gpracer1

Um, not quite.
Im gonna have to do the long version.

Your radiator is designed to outcool any amount of heat your stock engine can put out. Of course this means load = engine speed = vehicle speed (as in airflow). In other words no holding at full load at 6k rpm and only going 50 mph in first pulling a trailer up a hill with a tail wind. There wont be enough air flow for the amount of heat generated and the high volume of coolant going through the radiator.....we all agree it would overheat.

One might think that a bigger thermostat should cool even better?
No.

A thermostat does not control the heat of the cooling system. It is controlled by the heat of the system. The radiators airflow and coolant flow are what control the temp of the engine (Obviously so does the go pedal since it generates the heat).

You have a cold engine, the thermo is closed untill it heats up to 195 or so. Then it slowly opens (yes it has variable opening capabilities) and when the cold rush of the radiator hits it , it closes almost all the way, but still circulates. If you sit at idle for 1 hour: the temp keeps going up since there is no *air flow* <---temp regulating factor, so the thermostat opens up more which gives more flow. No air flow and the whole system gets hotter. No fans and it over heats. But the fans come on and the fans can remove more heat than is made by the motor at idle so it overcools the coolant (not the mteal motor where the temp sensor is located). The thermostat now starts to sense 160 water and starts to close slightly. (its like driving on a hilly road and holding 60 mph. You dont stab and let go of the throtle). The fans are still on for a moment and the coolant in the motor cirulates a little slower and holds to around 195-200 (how my fans are programmed).

Now you are doing 70mph with the cruise on. Tons of airflow, way more than needed. The radiator can waaaaay outcool the engine at this speed and load. (if you sat at your desk at work doing nothing and breathed pure oxygen, your mouth *thermostat* would only open 5 times a minute for air instead of 20)
When you are cruising down the road at anytime, it DOES NOT mean your thermostat is ever open all the way. It is a metering device, not and open and shut door.
So at 70mph your system is at 198 degrees. Now you open your thermostat wide open more than normal operation because its stuck. You will probably get a motor that starts to get hotter and hotter since it would flow past the radiator too fast to cool down the water in the radiator. Depending factors are speed , load, rpms and what kind of car you have (as in cooling system capacity.) Driving at higher rpms could aggravate the problem, since now your stuck open thermo is not metering and your rpms are dictating the flow.
Some cars overheat, some cars overcool with a stuck thermo. Depends on driving conditions, airflow and cooling system capacity.


Im not the resident expert, but I did go to school to work on cars and been an ASE master tech since '90.
Any of this make any sense?