When you got the car did it have dexcool or did you switch to it?

 

It has always had Dexcool, I've never mixed with green or switched.

 

It's the system pressure that raises the boiling point. Coolant, or anti-freeze as I like to call it lowers the freezing point of the fluid the 'richer' it is mixed. Do you have pressure on the system after it's been running? The hoses should be hard or rigid but be careful - I'm sure you already know this - they're hot. If you can pinch the hose while it's running and warmed up, you have a non-sealed system and it will boil over at a lower temp than normal. The usual culprit is the cap but could be anything from a loose clamp to cracked and deteriorated hose. Since there are no obvious leaks I'm thinking the cap or it's mating surface on the radiator neck. Make sure it's clean and no damage and try the GM cap. Check the bleeders for damage from overtightening, too. It'll damage the sealing surface and bleed off pressure.

It really sounds like there isn't enough pressure in the system to prevent boil over at operating temp. Good luck with this.

 

When you shut the car off it gets heat soak,from no longer having coolant flow.The heat is equaling out thru the motor.I suggest a different cap.Other possibiltity is a slight head gasket leak.

 

Is it a little rough on start up?
This is what head gaskets that are blown can cause.

 

No it's not rough on startup. The car runs marvelously. I ran it through the rev range on the test drive, once it warmed up. Ran very strong.

 

Fixed. I feel like the dumbest person alive. I had the overflow and TB hoses reversed, system was not able to pressurize.

 

how do you tell the difference between the two?