Have a 3.8 Litre, automatic -- Problem started with loss of heat and the heat guage going high. Have replaced Thermostat, and there was a leak in the rad. and that has been replaced.

Problem continues - seems fine for about 30 - 40 minutes and then I loose heat and the Temp Guage goes up . It , sometimes remedies itself and other times the antifreeze gathers in the overflow tank - have also replaced the rad cap.

Heater core or Head Gasket comes to mind, but both are expensive to have done.

Does anyone have any ideas that may solve my problem?

Thanks in advance for any help

 

Make sure there is no air in the cooling system. Follow the coolant R&R procedure in autolibrary.org below.

Failing that, and knowing the 3.8's history, a head gasket probem is likely