Hey everyone so today is the first significant rain of the season so quick story i used my climate control to prevent fogging on my drive to work and when i parked i saw a huge steam cloud coming from the driver side of the engine. I pop the hood and coolant is leaking out from the expansion tank. The car didnt over heat but i want to know why its boiling over like it did. I didnt use the ac or heater just hit the econ button directed air to the windshield. Its the first time that happens and prior to this i hadn't used the climate control ina while.

Help.

2001 Audi A6 Avant quattro 2.8 V6 177,150 miles

 

Get the coolant system pressure tested. That will tell you where the leak is occurring to allow it to boil like you're describing. Assuming the cap itself isn't defective, that is.

 

If someone changed the fluid recently and did not bleed the system properly and this is the first time the heat was on you could have had a lot of air in the system which expanded when it got into the hot engine.

 

@ Nebuchadnezzar and ManyAudis: ok before anything the other day I went to a shop that works with Audi and other euro cars and I was ready to get it pressure tested when the guy told me that if I do it I run the risk of blowing out an o ring or coolant hose that might be bad since its "forcing" the system. Was he right? I replaced the cap back in may of this year so the cap can be removed from the list. About a week and a half ago I did an inspection and did find some dried coolant around the CTS so i am suspecting that and I also have a feeling that the coolant flange is leaking because my level drops over night only during the day the coolant stays level. In the morning when I start it up but don't move it I then see coolant dripping from the back and if I jack the car up from one side up front what ever coolant is pooled somewhere drips onto the ground. Up front no visible leaks of coolant. Sorry for the long post guys

 

Update I drove home from work without using the climate control and it did not boil over. When it boiled over on the way to work used the Econ button and set it at 68 degrees with the air directed to the windshield. The oil temp gauge and the coolant gauge stayed at normal temp.