When you aren't getting heat, are both heater core inlet and outlet lines hot? IF the outlet is not hot but inlet is, the heater core is plugged.
There was a redesign of the heater core hoses that ford came out with and also a rediesigned water pump.
If you replace the water pump use a new one. Is this a gaurentee. No. But I have come across this and pump looked fine, but it took care of the problem.
Friday, October 12th, 2007 AT 6:18 AM