Gagestang

Alright, so I start the car up , car idles and runs good, so I drive down the road and shift at 3000rmp and its fine, then if I rev the car over 4000 when I shift the car will start to over heat after about 5 mins after being ran hard and stay hot , it has a 180degree thermostat in it ,

Gagestang

I know it sounds crazy , that's why I'm looking for some help , I have never seen any of my past mustangs do this

dawson1112

How was your head gasket checked?

Gagestang

We used a block tester

Duncan_GT

Are they new head gaskets?

Gagestang

I'm not sure i just got the car about a week ago

dawson1112

So you ran the cylinders up to around 120 psi with the block tester?

Im not so sure I would rule out a head gasket that is starting to fail .
Get a kit from autozone or similar that check for the presence of carbon monixide in the antifreeze.

When the cylinder fires it is pushing far more than any tester can run up to especially at high rpms.

Gagestang

The block tester they gave me was a liitle tube looking thing with some blue liquid , And pumped it and it was supposed to turn yellow if their was a problem , and it turned green I didn't test the psi in the cylinders ,

dawson1112

Ohh I got ya I was thinking of something else then. I think what you did was test for carbon in the coolant. You basically just sucked up the coolant and it mixed with that blue liquid.

Gagestang

Maybe the radiator is clogged somewhere , or maybe a collapsed lower radiator hose