12-10-07, 10:39 AM
I drive a 99 deville, and when I check the coolant level, there's a release of pressure, like, you're opening a bottle- not a huge release, but just a quick escape of air. Is that the exhaust from the head gaskets causing that? The coolant level hasn't dropped at all, and temp stays steady. This may sound like a stupid question, but the Eldorado I had before never did this.
12-10-07, 12:29 PM
Pressure in the surge tank is completely normal as it is the top of a sealed pressurized system. Look at the cap and it will say "16 lb." That's the pressure it will take to open the cap vent. The system is pressurized in order to increase the heat transfer between metal and coolant as well as, in conjunction with the coolant properties, raise the boiling point of the system. (The coolant normally operates at around 206 - 215 deg.F) Never release pressure while the engine is hot or warm. You may get an instant boilover and incur severe burns. On the other hand, there should be NO pressure in the tank with the engine cold. Everything cools down and contracts, so no pressure. (Maybe even a little vacuum if the cap check valves are a touch "sticky". Not to worry.)