I have a 1997 f150 4.6l. The truck overheats if it does not warm up at idle for
20 minutes before driving. The first sign is loss of heat - temp gauge spikes and then blows antifreeze out of the overflow. If warmed up first, the truck seems to run fine. Changed tstat and pressure tested the system - no loss or gain in pressure while at idle. Why would the truck only overheat if not allowed to warm up? We live in New York and this problem only started after winter arrived. Any ideas....
