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Bubbles in cooling system

My 1999 Venture van was losing cooling fluid. The dealer siad it was reaparable if they replaced the water pump and cylinder gasket for $1500 dollars. The van has 120,000 miles on it, but my wife and I have had a lot of fun with it nad did not want to buy a new car at this time, so I had it done,

It seemed to be OK, but a few weeks later it overheated (the temperature dial went over to the red and the temperature alert light came on. I could stop not stop quickly on the freeway, but within a few second the temerature dial went back and the alert light went out. I went back to the dealer and he said I have a bubble in thge cooling system, this sometimes happens with this type of repare but they can not fix it. Is this true?

It is possible. When refilling the system sometimes a little air gets caught in the system. Usually it works its way out safely. If there was much then you would have needed some additional coolant.

An airlock is possible if they didn’t refill the cooling system correctly, air can locked up in the heater matrix. But they should have done the job properly and purged the air as part of the repair. It shouldn’t happen again though, if more vapor (air or otherwise) is getting into the cooling system then you either have a cylinder head or inlet manifold leak.

As for “it can’t be fixed”, that’s pure nonsense. You’ve already paid for it to be fixed “fit for purpose” i.e. not leak and not overheat.

If the intake manifold gasket hasn’t been replaced with the new revised one you may have a leaking one in the future if not now.

It’s a notoriously common fault with GMs 3.4L engines (1997 to 2003). Been there.

Keep an eye on the coolant level in the coolant reservoir.

sounds like it was probably air in the system but i will say had i worked on it you would not have gotten it back until the air was completely purged from the system. i will let it sit in the stall next to me and run while i start the next job and keep an eye on it until heater blows warm and thermostat has opened and I am sure all air is gone I dont want a customer coming back in to ask me questions about stuff like that when im in the middle of something else or to worry that some wasnt right.