Water Boiling in coolant system

robbylance · 04-07-2012, 08:44 PM

I just replaced the heater core in our A6 as it had blown and water went all over the floor boards. It is now all fixed and works great. But...now the coolant keeps boiling out of the expansions tank. The heat works...the car temp does not go up...and the car is running fine. I just replaced the over flow bottle with a used one. Does anyone have any ideas???....Am I just not getting all the air out of the system???.....help!!!!

scarman · 04-08-2012, 07:31 AM

The V6 cooling system is more sensitive to air in the system than the I5 engine on vehicles on this forum. The thermostat and temperature sensors cannot perform well since air doesn't transmit heat as well as the coolant. This can result in hot spots around the cylinders and blow a headgasket or two, so this is not an issue to wait and see what happens.

I also tend to want to look at the last thing I touched for my problems. I haven't heard of anyone using a used expansion tank since new dealer parts are not that expensive from the many Audi dealers selling parts online at a significant discount. There have been many issues with new aftermarket tanks developing cracks, and so they are avoided by most owners here.

"Boiling out of the expansion tank" doesn't explain what is going on very well. Look over the new tank, and explain where the coolant is going. Maybe your "new" coolant tank has a faulty pressure relief in the cap.

robbylance · 04-09-2012, 07:45 AM

There was steam coming out of the expansion tank and water was boiling in the upper hose. But after 4 times bleeding the coolant system it stopped. Everything is working correctly and thank your for the responce.

04-08-2012, 07:31 AM	#2
scarman AudiWorld Senior Member Garage is empty, add now Join Date: Sep 2009 Location: Knoxville, TN Posts: 612	The V6 cooling system is more sensitive to air in the system than the I5 engine on vehicles on this forum. The thermostat and temperature sensors cannot perform well since air doesn't transmit heat as well as the coolant. This can result in hot spots around the cylinders and blow a headgasket or two, so this is not an issue to wait and see what happens. I also tend to want to look at the last thing I touched for my problems. I haven't heard of anyone using a used expansion tank since new dealer parts are not that expensive from the many Audi dealers selling parts online at a significant discount. There have been many issues with new aftermarket tanks developing cracks, and so they are avoided by most owners here. "Boiling out of the expansion tank" doesn't explain what is going on very well. Look over the new tank, and explain where the coolant is going. Maybe your "new" coolant tank has a faulty pressure relief in the cap. __________________ Tom '95 S6 '95.5 S6 avant

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04-09-2012, 07:45 AM	#3
robbylance AudiWorld Newcomer 1995 Audi A6 Join Date: Oct 2011 Posts: 9	There was steam coming out of the expansion tank and water was boiling in the upper hose. But after 4 times bleeding the coolant system it stopped. Everything is working correctly and thank your for the responce.