I had a customer call me last week with 15 LS460 Heater blowing cold air. I picked up car and sure enough when the car is warmed up to operating temp vehicle would blow cold air. Confussing a bit, I drove car home but I noticed when I took off and get to around 40 mph vehicle the heater would come on. There is a small bleeder valve on the top radiator hose that is a bleed valve for the coolant system. We bleed it out and bingo, we are aware of bleeding coolant system allthough I had never seen it happen on vehicle with no repairs being done before. Customer claimed car never worked on but by me. I hope this can help someone down the line.

 

Thanks for sharing this info. Any idea what caused this issue?

 

It’s 2020 isn’t it time for a coolant flush and change anyways?

 

Low coolant , or low coolant due to the valley plate leaking.

 

Apex this thread is almost 3 years old.

 

do you know if it ever needed the valley plate resealed?!

 

had the same exact issue- found out had a valley pan gasket leak. Got that done and heat works perfectly fine. Btw I did check the bleeder and the coolant cap first before inspecting for the leak.