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Air in the cooling system


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For anybody who follwed my problem with loss of coolant on my 97 aurora I have a question. I just read a post by "rrdrerup115" about the sound of liquid running through the system. To really quickly summurize my problem I have a coolant leak through my surge tank cap. For now as the level dropped a little (not enough to make the message flash - yet anyways) the coolant seems to be very very slowly dripping from the cap. The thing is that I also can hear the liquid running especially when I'm stopped at a light and then when it comes time to go and i step on the gas i can hear as if the liquid was running. Someone suggested that it might be air trapped in the system. Is this at all possible? How would I go about checkin if that is what may be causing my problem? How would I go about fixing it? I think if it is possible that it would make sense because my problem started after I had a hose blow up and most of my coolant was lost. I simply replaced the lower rad hose and filled up the system with fresh coolant. Could that cause air in the system? Anyways I was just thinking outloud...any thoughts on this are really appreciated. Thanks

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take the cap off of the resivor when the engine is cold start the car and bring it to running temperture. As the air is purged from the engine you may see bubbling in the resivor and the collant level will fall. Top it off. If the it continues to boil/bubble air or probably exhaust is entering the system and there will be a residue in the resivior. If you know that is not the problem because you're not leaving smoke screens when accelertaing from idle then change the radiator cap its probably not holding the pressure. Those are the first things to look at if its not overheating or running above normal its probably not the termastat or pump.


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If I recall correctly, there is no water valve to control the flow like that found on older cars. The water circulation through the heater coil occurs at all times when the engine is running.

It sounds like you do have air in the system, though it's a concern that it won't move to the surge tank and stay there.

Best options are to remove the cap, start the car and let it run until the thermostat starts to open. Run the thottle up a little to circulate the water (expell air to the expansion tank). Don't do this too long so you can avoid boiling off of your coolant.

On the dark side, you may have a more serious problem. If you popped a hose and have high miles (e.g. over 75K) on the car, you might want to have the engine checked for a blown head gasket.

Basic tell-tale stuff is a pressure (water) release at the surge tank or leak at the water pump shaft seal, a strange smell when you take the cap off the surge tank (smells like wet exhaust) or a continuous loss of coolant. In some cases the cooling system will stay pressurized even after the engine has cooled off overnight. Take the cap off in the morning and see if it gives a short "sprishhh".

Good luck.

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It would seem that the cooling system would purge the air at normal operating temperature and normal operating speed. Maybe not, but it would seem that way.

Let's not even go down the dark road that jhall mentions.

The thing that jumped out at me as I was reading and before I read any other replies was you comment about coolant leaking from the surge cap. If the cap isn't holding pressure, the coolant has a lower boiling point. For instance, h20 at 14.7 psi of air pressures boils @ 212' or @ 100' in countries that use more logical measureing systems. If you bump the air pressure up an additional 15 pounds, the boling point increases--I don't know 240'/260'. If you are located at an a high elevation, lower air pressure than 14.7 psi, water's boiling point is lower than 212.

The fist rule of coolant system troubleshooting is to verify that the system holds the required pressure. If the system doesn't hold the required pressure, the next step is to correct whatever is responsible for the system not holding pressure. If you don't verify and/or correct this first step, you're pissing in the wind if you are addressing anything else.

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I had a real experience with a plugged vapor vent line on my 94 SLS.

I had the expansion tank off and left it outside while I changed the engine. While it was off some critter decided to make her nest in the vapor hose. I didn't notice it when I put it back on the car. (I usually check for stuff like that out, but I was in a hurry.) ;)

Needless to say, it didn't vent and I could get about 5 miles before the temp started getting above 230. I' would stop & let her cool down & then turned around and went back home. Got hot again. I then took the vapor hose off at the engine connection and it was a couple of seconds before any antifreeze showed up. But nothing was comming out of the hose fromt the expansion tank even though it was topped off! (for checking purposes) I removed the hose and It was plugged tight enough that it took 120 psi to blow the remains of the nest out of the hose. The anti freeze drained out of the connection as soon as I removed the hose from the tank. After clearing the hose, I put it all back togeather, refilled the system and have put about 15,000 miles on it since with no problems. The reason that it got hot in my case, was because the system was completely drained. As a result, there was a very large airpocket in the engine. I'm just glad that I didn't overheat it enough to cause more problems.

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