I got a coolant problem.About a week ago My 2001 F150 5.4 would not heat very well. So I put a new stat in and everything seemed fine until I drove it the next morning and that is when it happened. I drove it for about 4 miles, Good heat and then no heat, Temp started to rise to almost redline and then dropped back down, started to heat again. This happened for 2 days in a row. So I thought bad stat again, changed it out and does the same thing. Also It sometimes burbs out fluid out of the cap when this happens. Waterpump Maybe? Please help!

It only seems to happen after the engine cools for about 8 hrs or so and then it is fine if you keep driving it!

Rainman2

 

You have an air pocket. Make sure the over fill is toped off and it should add it automatically.

 

+1
There is air in the system.

 

To what extent did you drain ? Regardless , eliminate the block air if any - Fill thru the degas with the top of the hose disconnect on top of the pump.

When coolant starts to make it's way out, connect the hose and fill the rest of the way..

 

I have two E150 vans w / 5.L motors with the same problem about the heat gauge up and down temp reading it sure looks like an air lock however it's ok in the summer months, (hot days) but when the temp get's about -17c to -22c the problem repeats almost daily. these vans are used for servicing. never did find out what doing that one van has 340000K the other 148000k. w/same problem.
roltech

 

Is your anti-freeze mixture strong enough?