5.4 2003 f150 coolant issue

just bought 2003 king ranch with a 5.4 it started burping coolant and the heat was comming on then while the engine was at operating temp would blow cold air.then the temp gage would start to rise,once it got to the top the heat would start to come on and the temp gage would then go down to normal.I started by changing the thermostat which didnt help. then i figured it was air in the system I kept burping the truck at idle but it never helped, it kept burping while driving all the coolant out that i put in back out finally i took that cap off the one that clicks when you tighten it and replaced it with a cap that tightens down all the way and dosent click. every morning i check the resivoure fill it up to the proper level and so far so good i hope this helps

just bought 2003 king ranch with a 5.4 it started burping coolant and the heat was comming on then while the engine was at operating temp would blow cold air.then the temp gage would start to rise,once it got to the top the heat would start to come on and the temp gage would then go down to normal.I started by changing the thermostat which didnt help. then i figured it was air in the system I kept burping the truck at idle but it never helped, it kept burping while driving all the coolant out that i put in back out finally i took that cap off the one that clicks when you tighten it and replaced it with a cap that tightens down all the way and dosent click. every morning i check the resivoure fill it up to the proper level and so far so good i hope this helps
I would look at the centrifugal clutch on the fan if leaking oil replace. Are any fan blades broken. Watch if any of the radiator hoses are collapsed. Is the belt for the water pump tight? Is the fan shroud broken? Feel top and bottom radiator hoses hot when up to temperature. A plugged radiator can cause problems.

no more issues after about 3 weeks of driving with new cap took that long to get all air out of system cheep fix hope this helps someone

I hope your new cap solves the issue. I had a 2000 F150 5.4 and had issues with the temperature also rising and falling. Also replaced the thermostat. Ok for a few weeks. Then the stuff hit the fan so to speak. It started again and I went this time to a mechanic. They did a hydrocarbon test on the coolant. If it turned one color ( not sure which it was) then the head gasket was bad. I was getting exhaust gases in the coolant and causing it to overflow. I hope this is not your issue but watch out.