KyMustang

I have a 1991 Mustang. My father and I rebuilt the motor and it is now a 306 We put AFR 165 trick flow intake, 70mm throttle body, 75mm mase air. Start it for the first time last night, however, after 2-3minutes the temp gauge goes past 270degree. But when you turn on the heater it goes back to normal.

KyMustang

If you have any suggest I would welcome them. Thanks

Aussiblue

possibilities include:

Stuck thermostat or thermostat not in correct position.
Cooling system not bled when filled to prevent air lock in system.
Fan connected back to front. Blowing instead of sucking air.

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Regards Blue