Overheating Issue and purging the radiator

2004 3.4

I've had a problem with the car overheating first thing after i start it and drive a few miles. the car would overheat, coolant would bubble out of the overflow, then the car temp guage would suddenly drop and the car would run at varying temps between 180-210, spiking then suddenly dropping.
I changed the thermostat thinking it was sticking.
it was fine for 2 days then the car overheated again yesterday on the way to work and went back to normal. I topped it off before driving home (and get this) The temp ran at a steady 140-150. I commuted for an hour at that operating temp.. I believed the guage was lying to me, I could touch any part of the engine except the exhaust manifold and the engine was cool... I don't get that.

second symptom: sometimes i hear liqid flush when i step on the gas, same sound you hear downstairs when someone flushes a toilet and the water runs down the pipes..

I can't find any evidence of a leak. the water pump is less than 3 years old, the thermostat is only days old.

What else do I need to look at, and how do i purge air from the coolant system?

This sounds like a head gasket problem to me. I have a van with the 3.4 and what had happened was the head gasket starts to go. When you first start the car, the compression leaks into your coolant system as air and blows out some coolant to make room. No you have an air pocket in the coolant system. The leaky head gasket seals when the engine warms up and your fine, except for the air pocket. This may resolve itself with enough driving. The problem is, the next time you start it when cold, you repeat the process. Does it ever run rough when you first stat it cold? I would have a compression test done on it.

Tend to agree with rkvons on this........an air pocket is being created by a leak.......since it doesn't seem to be external(checked the usual places? W/p, condensate drain, radiator hoses, radiator, heater hoses, etc.,......and ESPECIALLY, the lower intake, looking closely under the throttle body and the P/S pump with a light), then it's internal.....

It could be a head gasket or lower intake gasket.......one way to check for external leaks and a head gasket leak, is rent a coolant pressure tester......pressurize the system with the engine warm, not hot.......leave it pressurized overnight.........next day remove all spark plugs, disable fuel(disconnect injector harness) and spark(2 wire connector on ICM, passenger side)......have someone crank the vehicle.......if you see any coolant come out of the spark plug holes while someone cranks the vehicle, then you have a head gasket problem......if nothing comes out, double check for an external leak, especially at the lower intake....

That's not good news guys. You were supposed to give me good news.

Yes sometimes it does run rough when first started. It only take a small Rev of the engine and it idles normal. Guess I'll find myself a pressure tester.

If you are losing coolant, have a rough idle initially on start up, then like rkvons said, could have coolant in a cylinder......more often than not, it will be cylinder #1, rear of engine, passenger side...

That's not good news guys. You were supposed to give me good news.

Yes sometimes it does run rough when first started. It only take a small Rev of the engine and it idles normal. Guess I'll find myself a pressure tester.

what coolant is in there ? how did you maintain the coolant system ?

if you have the proper coolant and have properly added the correct amount of antifreeze , you can add some bars stop leak....that is IF you have a properly maintained //// clean coolant system....

If this fails you may have a bad/large head gasket leak or a cracked head... if the bars stop leak works no big problem if the stop leak does nothing after a few hundred you will need serious work to fix this...

sounds like your coolant system is not pressurizing. if there is no pressure the coolant will turn to steam and the temp guage will drop. might have a blown head gasket, look for other leaks that might be masked by the boil over out of the bottle.

I haven't run the car since reading about the head gasket. I had it towed off to a mechanic today since this is not a job i feel like taking on.

the car is a 3.4 with 130,000 miles on it. I've replaced the transmission in the last few weeks, and now the head gasket. I plan to have the timing belt done while it's in the shop.

is there anything else i should consider doing as maintenance at this milage? I'd rather take the hit now than be surprised later.