: Doesn't seem to be the head gasket but still overheats

10-20-11, 09:33 PM
I have a 99 Cadillac Eldorado. The first time the car overheated was because tension pulley for the water pump broke. I replaced it and continue to drive the car as normal but always put coolant in it before I left the house. Normally only drive about 30 min and every thing was fine. Drove it about an hour and it got hot.Let it cool put in more coolant drove home. Started looking for leaks and replaced the thermostat, the radiator and both hoses, the water pump and the gasket. After reading many posts on here I took out the spark plugs and put 120 lb pressure in each cylinder. Did not see any air bubbles in the surge tank. Gave up and took it to a trusted mechanic. He replace the surge tank cap and the thermostat. Put 12 lbs pressure in the coolant system. It held that pressure all day (8 hours). He thinks it is strange how the car runs at normal temperature and then quickly overheats. It is not a slow progression (only seconds). He thinks it may have air in the system causing it not to circulate. Any ideas on burping the system or what other problem it might be?

10-20-11, 09:53 PM
The system is self purging. Do a search for "purge line" and read up on it. Clear the obstruction at the hollow bolt at the water pump end if you find one. If not, then get a block test kit and check for exhaust gases in the surge tank.

10-21-11, 11:36 AM
What is the indication for this "overheat" ? Gauge position, coolant blowing out the reservoir cap relief.............? Several seconds from normal to overheat is pretty fast for that much temp change. If there's no physical indication present, then electrical (gauge wiring/sending unit) is suspect.

10-21-11, 05:47 PM
When the head gasket was bad in my 98 Deville, I put 120 psi air into each cylinder, and I actually had to do it twice. I had expected to find a good amount of bubbles, due to the fact the car would not make it over a large hill without overheating. First time, nothing, so I did it again. All I got was a very, very, slight gurgling noise when air was put into no.1 cylinder. Upon teardown, I could see just a tiny spot between no. 1 cylinder and the water jacket where the gasket was shiny. Remember, we are talking combustion chamber pressures here. It doesn't take much of a breech with that much pressure to displace the coolant. My point here is that sometimes the leakage is such a small amount, it is easy to miss.

10-21-11, 09:01 PM

10-23-11, 07:39 PM
The only indication is the gauge position. I will check the electrical (gauge wiring/sending unit).

10-25-11, 05:40 PM
We hear time and time again from people that have overheating problems, and when they can't pinpoint the problem, they start to replace everything they can easily replace - I actually don't really blame them, but on a N*, it is almost invariably the good old pulled threads/head gasket problem. The only thing I would say is, keep driving it when it starts to overheat - if it is the HG, it will puke out all the coolant in short order and go into limp mode.

10-25-11, 09:45 PM