1998 f150 4x4 4.6l vin w ! Cooling system has been flushed, new heater core, water pump , and thermostat ! Ok here's the problem ! It over heats , if your try and burp the system by driving around with the overflow cap loose and get it warmed up then tighten the cap and you can drive it around all day with no problem ! Once it cools down and then you drive it with the cap tight it will over heat ! The heat in the truck is warm then it gets cold and then over heats ! And the upper radiator hose is super hard !! Head gasket Maby ? Did a combustion gas test and didn't come back positive any help thanks

 

Intake gaskets, hole in the radiator or hose.

 

Well it's not a hole in radiator or hose, I did a pressure test and there was no leaks !!!

 

Did you drain the block when you did the flush? I am thinking you have a blockage in the block of your engine that is preventing you from getting good circulation in your cooling system.

 

Ok last chance before I pull the heads! I replaced the radiator with no luck!! Next I'm going to pull the thermostat and start the engine so I can see down in the thermostat housing and try to see if there is any bubbles , if so heads are coming off this weekend!!! And before anyone comments on it, I'm taking the serp belt off when I do this!

 

Could be a crack in the intake manifold at the coolant cross over. They like to break there

 

How could that cause a over heat issue? I pressure tested the cooling system to 15 psi and theirs no leaks that I could see anywhere!!!

 

Have you check your oil? Look for coolant, it will float. Look on the top of your oil cap for milky substance. Whats your exhaust look like, any coolant smell there?

I had a similar issue and had an intake gasket blown right where the heater core hose is at intake #1.

 

I have checked the oil, it looks fine!

 

And it can't be the intake gasket causing this situation . The intake gasket has no connection to the combustion chamber, it only could leak externally or internally into the intake runners which would cause white smoke and I don't have that, I'm only loosing coolent when it over heats bec it comes out the over flow!