97 F150/4.2
Heat loss while driving and then the gage temp Gage went sky high. Then it went back to normal but no heat. Added anti freeze because it was very low. I had no signs of external leak but was told E6 miss firing???? Should I be concerned in looking for future signs. Also what could this eventually mean?

 

mileage? does it have the original intake gaskets/seals? what kind of condition does the coolant look like? do you see alot of white smoke from the tailpipe? smell antifreeze? is your passenger side floor getting wet?

 

You got an air pocket thats why the fluctuation. I would lean towards bad head gasket because your reporting a missfire. Never heard of the E6 though whats that? check engine light on? running ruff? Get the real code pulled. If its something like p303 you probably need head gaskets. You would then want a pressure test to confirm and of course pull that plug and see what it looks like.

 

The 97 4.2 had the bad intake manifold gaskets. If you keep driving it, you will probably hydrolock it. Yes, you need to be VERY concerned.