I have an 07 V6. I first noticed my heater was not working. I checked the coolant and it was almost empty. I filled it up, heater worked again, but then later that day on my way home from work the heater stopped working again. I pulled over and it was empty again.

I noticed a small gap in the t-stat housing. I replaced the whole housing, t-stat and o-ring, and filled it back up with coolant. Drove around for 30-45 min and it was running just fine, couldn't smell the coolant, heater was working good... I get back home and over half of the coolant was gone.

The housing is dry, the block that the housing sits on is dry, I don't see any wet spots on the engine or any hoses. But if I look under the car at the engine, there is a long metal piece (not sure what it is called) that runs under the engine almost from the driver wheel to the passanger wheel. I will attach a pic later today or over the weekend. Anyways, that metal piece is soaked. Is there a hose that runs right above that piece that might have a leak? What else could it be? Thanks everyone!

 

It could be a small leak that doesn't drip but comes out as steam. Or it could be a blown head gasket and the coolant is going into your engine. Is white smoke coming from our exhaust?

 

There was some white smoke when I first started it, but then didn't notice any later. I figured it was because of the cold weather. I will check when I get home. If there is white smoke, does that mean there is a blown head gasket?

 

White smoke means the coolant is burning in your engine. Could be blown gasket or cracked head or block.

 

Well it isn't blowing white smoke, so that's good!

These two pics are the only parts I see under the hood that looks wet. I couldn't find anything else. When I started the car and let it warm up, I didn't see any leaking fluid, so I'm thinking it only leaks when I'n driving, or maybe I didn't let the car warm up long enough.

 

Rent a radiator pressure tester from your local auto parts store and run a pressure test on your cooling system. Set the pressure to match the radiator caps pressure rating. With everything working properly, the pressure should hold longer then 15 minutes. If pressure drops, then you have a leak. If the leak is external (which is most common) you should be able to see the leak pretty easily and possibly even hear it hissing. Good luck...

 

the water pump has a small weep hole you should look at, and it might just be a hose or even just the cap. the pressure tester should find it like said