Joe_5.0L

I have a 1990 mustang gt, I've put a new crate engine in (long block) & have less than 50k miles on it. But I've been blowing radiators & heater cores & the upper intake manifold gets extremely hot. My temp gage reads where it should, right in the middle & it does work... the car runs great, just really hot. I don't have oil in my radiator and no water in my oil... anyone have any idea why it could be running so hot? Intake is stock (it is getting so hot that the paint is baking right behind the egr spacer) I need help/things to try I've got a new radiator in, new water pump, I've bypassed the heater core due to the pressure, what could cause this?
Thanks,
Joe

AzPete

Do you have cylinder compression leaking into the coolant....that would possibly cause the pressure and heat.

88 orangepeel notch

First thing to do is get an infrared thermometer, those kind with the laser, and check actual temp of thermostat housing at operating temperature. Foxbody gauges are notorious for being inaccurate. Don't trust the stock gauges. Let us know what is.

Blowing radiators and heater cores really doesn't have much to do with the hot your coolant gets, but the pressure, so check your radiator cap, or just get a new one with the correct pressure rating.

tw1234

Rad cap as mentioned above; Thermostat stuck closed or installed upside down? 50/50 Antifreeze mix must be used not just plain water or it will boil at 212 F.