: too hot and too cold

12-19-05, 12:59 PM
I've had my car since April and have put 10000 miles on it. It now has 60000. They tell me the car has already been timeserted but it was'nt the heads that were done; it was the halves that were done. In June I took my car to the cadillac dealer and the said my car overheated because I have traces of exhaust in my fluid. I then took the car to my mechanic and he did'nt check that but did pressurize the system and supposedly found my lower rad hose leaking and fixed it. I never add any coolant. The car did warm up in the summer months while climbing hills at slow speed. When I climbed hills quickly though the car did not warm up. Now that winter is here the car cools down when I start traveling down the highway. It warms up while idling. I just think the stat is sticking. The dealer is telling me they need to replave the stat and the housing. I can not understand why they would replace the housing. They also said the housing was leaking. Like I said I never need to add any coolant and the engine was just presure checked in June. They also said they don't know if replacing the stat will fix my problem. Also since my car is running so cool it is wasting gas. I had too also put cardboard in front of the radiator just to get the stat to run between the first and second mark on the guage. Anyhow it seems to me that if I had a head gasket problem I would have no problem warming the engine in the winter. Hopefully someone has some ideas for me. I'm not ruling out a headgasket but it must be a very small leak if there is one and maybe it will not get any worse.

12-19-05, 03:06 PM
I understand there is an updated thermostat housing/water pump cover for the FWD Northstar engines. If the seal on your current housing is leaking, I understand Cadillac recommends to install the updated design, although I don't know what all has changed. You should be able to purchase a new seal for your current housing for minimal cash. The thermostat is also cheap. You can do this job yourself in about an hour in your garage. Let us know if you have any questions.

12-19-05, 03:12 PM
Oh thats probably why they want to replace the housing then. They could have just told me that at the dealer,huh? The dealer called and said they would replace the stat but it would'nt last due to my headgasket problem. They say the pressure change in my engine due to my headgasket failure will probably damage the new stat. I am still interested to find out if anyone has any ideas on my too hot or too cold problem.

12-19-05, 08:32 PM
What year car and more importantly, what engine are we talking about.

12-21-05, 07:22 PM
My car is a 99 deville concours with the code 9 motor which I`m being told isn`t available anymore from the factory. It`s the 4.6 northstar that I believe all the devilles have for that year. I just had the stat replace today at a local garage and the car is warming up just fine for now. The dealership claims since the head gaskets are blown that the pressure is changed in the engine and the new stat will not last.

12-21-05, 10:05 PM
This all sounds a little fishy. First, case half does not need to be "Timserted" when done to my knowledge. Did they do a cylinder leakdown test to determine a head gasket problem? I think a second opinion might be in order.

12-26-05, 05:35 PM
No they did not do a leak down test. I bet I'll find out this summer if the car gets hot again. I have heard from some of the posts here that if they do pressurize the cylinders that it will ruin the head gaskets for sure.

12-26-05, 06:50 PM
That is rediculous. When doing a leak down test, you pump shop air (125-150 psi) into the cylinders. I do not know what the cylinder pressures are when the egine is in operation but I suspect it is well over 1000 psi.

12-27-05, 01:59 AM
Indeed. With 10.3:1 it should be over 150psi just cranking. Then when the mixture's ignited it would be dozens if not hundreds of times higher...

12-27-05, 09:23 AM
I suspect what the dealer service was trying to describe is ruptured H gasket will allow hot ex gas into cooling system creating hot pockets as gas displaces coolant and a pockt of hot exhust does in deed Toast the the thermostat. It fails in a CLOSED position!

There is a suspicion that many N* engines are succesfully drived w slightly low amount of coolant in system and then later problems can and do develop .

Certifiy that you have the proper coolant mix, FULL COOLANT and a GM thermostat. Change thermostats often because housing on the wax motor is
thin ALLOY.

I just had the thermostat housing replaced w updated one METAL w replced the orig factory plastic housing. They failed to supply shorter bolts and it leaked.

I hope you now have a stable cooling system

12-27-05, 05:39 PM
Thanks c170B. Now I know why they have an updated stat housing. I had a local shop replace my stat since the dealer did'nt have the new housing and I don't know if they replaced with a GM stat. Probably not. The car seems fine for now. If I have to replace then next time I will get the new housing.

12-27-05, 05:42 PM
Hey C170B! The stat info was good news. My stat could'nt have been closed because my car cooled down when traveling down the highway. That may mean that i don't have a h gasket problem after all.