Ok i have had an issue with my car and figured the result would be getting a new radiator cap from the dealer because after reading many posts saying the aftermarket ones are not the right ones. So i bought 2, 1 for each car. Now they are both doing the same thing. They are running hotter than normal and the thermostat seems not to open all of the hoses get real hard with pressure. But if you back off the radiator cap 1 notch, ya know how it has 2 notches/locks, well if you just turn it back one then everything seems to circulate fine. So what is with these dealer caps????

Justin

What is the part number on the caps that the dealer sold you ?

The radiator cap I have found on on Fieros from the factory is p/n RC27.
The part number from GM is p/n 10409635.

I use a Stant cap, p/n 11330, which is a non-vented cap with the Lev-R-Vent lever to vent coolant pressure before opening.

Yes that is the part number that i have in there now, why would these GM parts be doing this to my cars?

When you replace the cap did you purge all the air out of the system again?
If your getting pressure then it is working right if it is building pressure. The wrong cap just allows coolant to run out when the system is cool since the disk drops and allows the coolant to run out since the rad. is lower.
Sounds more like you have air left in the system.

But it is doing it to both of my cars and one of them all i did was change the rad cap, the other is the one that may have air in it but the other deff does not.