Hi we have a 2002 cadillac DTS. My husband has put in a new rad, and temp gage. I will be driving the car for sometimes 20 min sometimes an hour then it will say engine hot turn off a/c. My heat will stop blowing hot and blow cold. Can anyone please help.

 

i dont understand this part "My heat will stop blowing hot and blow cold"
a/c is off correct

 

The A/C is off we will have the heat on and then all of a sudden it starts to blow cold. We are thinking there is air in the coolant system due to a blow head gasket.

 

well there is a leak in the system meaning no coolant in the heater core
either u have an air bubble in the system or there is another leak

 

While this condition makes us quickly turn to head gasket problem there are many areas to investigate for leaks in a Northstar of this age.

Radiator tanks are plastic and are prone to cracking as they age so rule that out.

Coolant overflow bottle is another plastic piece, prone to deteriorating over time and I have seen the tube fitting that runs from the bottle to the radiator crack and leak.

Water pump could be leaking and due to heat and driving the coolant evaporates away from view.

If all these areas check out only then I would be suspecting the head gasket.

 

heater blowing cold air often signifies low coolant .. so .. when all this is going on, what happens to the coolant level?

that is really important to know.

another other thing is the driving conditions, weather temp, speed, etc..
there isa detailed thread in our FAQ section .. please take a look at it for other symptoms