I have a 2005 mc with the 3.4. been having problems with the coolent overflowing from the over flow bottle.water pump is new.took out thermostate and boiled it and it opens.flushed the coolent several times.no smoke from exust.head gasket and top/lower intake gaskets replaced about 30,000 miles ago.no puddles in drive way.no coolent in oil.
what happens is i drive the car only half a mile then "hot coolent temp" light comes on in the message center.(temp gauge is pegged)ill pull over and pop the hood and coolent is pouring from the overflow bottle.i can feel pressure in the upper and lower hoses.lower is cool to the touch and top is hotter then heck.if i open the bleeders,ill get air out of the right side and coolent from the left.the fans are also coming on.and the weird thing is i can drive around all day and have no problems and another day drive just a half mile then have the problem.thank you for your advice in advance!!

 

sounds like you air bubble stuck in your channels, just leave the bleeder open till your getting nothing but coolant coming out

 

If you have so much pressure in the system it's causing the coolant bottle to overflow, this is NOT good. Yes, you can get the temp gauge issues with an air pocket in the coolant system, but if the car has the appropriate amount of coolant (radiator is filled AND the bottle is at the appropriate line), even with the expansion of air/coolant due to rising temps, it should not be backing up so much in the overflow bottle that it's coming out. That's an indication that you have too much volume in the coolant system (can be air, can be coolant).

Before going crazy, first, make sure all the air is bled out of the system. If after a day or two you are STILL bleeding air, then you probably have bigger problems. A head gasket failure (despite being a new gasket) could be the issue. You may be getting compression gases forcing an air pocket into the coolant system.

My 3100 (same basic engine as your 3400) in my '94 Grand Am did that in '08 (at 180,000 miles). It began with a little rough idle for a couple of seconds on a cold start, then odd temp readings and constant air pockets. about a month later, the tell tale sign, big CLOUDS of white smoke from the exhaust. Changed the gaskets (they did crack) and the car runs great (drove it today over 214,000 on it).

FYI - If it IS compression gases, it can cause further problems. My Grand Am issue eventually blew the side tank gasket on the radiator when I finally found the problem. The compression gases are causing the system to hold beyond the 13-15lbs of pressure it was designed to manage. The weakest part will fail first adding more cost to the repair.

 

thank you all!havent drove it since the last time it "threw up"so im going to bleed it tomorrow then drive it.also going to get the strips to test the coolent for gases.thinking of pressure testing the cooling system and compression test.btw,when i stated the temp gauge is pegged its couse the gauge doesnt work.

 

sounds like air to me too. had a problem similar in my 91 lumina 3.1