Hey guys really sorry this is my first post here, I was just about to make one saying "Hey I bought a Ford, blah blah blah" but apparently this isnt the case.

The truck is a 91 F-150 4x4 with a 4.9.
Coolant is new and full, pressure tested all last night from 13 Psi, and in the morning it was at 5 or 6.

To start this truck has a history of going through waterpumps {one every 6-18 months}(all were Autosence rebuilt ones though, where one even had the wheel corrode away)


So, the truck has not been driven for about 8-9 months. Right before that it got a new rad, full coolant flush, full tune-up etc. A "new" waterpump only 13months ago.

When driving or letting it idle it will get up to temperature just fine but after awhile 7-15 mins the gauge starts to climb. It will not really stop climbing unless you shut the truck off. I have checked the truck with my Snap-on scanner and the ECT (engine coolant Temp) sensor is reading normal ~190-200F. I know there is a CPU and guage sender unit.

After letting it sit for a while with the key off and turning it back on in say...30 mins the gauge seems to just go up more from where it previously was. I know fords are famous for having issues with reading too cool all the time but this is definately a new one to me. I have let it sit for over an hour and the guage still read over full hot.

Some possible issues we have thought of are:

1. Sender unit is toast
2. Blockage in the coolant system around the headgasket area
3. Water pump not pumping coolant out of block once it warms

Tommorow I plan on changing out the sending unit, and trying a feel test. Just see If I can tell a difference from the front of the block vs. the back where the sender unit is. I am going to see if I can find an aftermarket temp sensor as well for testing purposes.

This problem really worries me alot and I am supposed to get it all transfered over tommorow but with this new discovery it will have to wait.
I appreciate any and ALL advice, opinions or ideas. Please feel free to comment.

Thank you very much for taking your time to read this.

*edit*By watching the temperature climb you can see the thermostat functioning when the gauge drops when it kicks in.**

 

Sounds like your on the right track. Make sure that your gauge and sending unit is actually working right before you try anything else. Check the thermastat that it is opening properly and replace if needed.

 

Thanks^^.

I should begin testing in about 2h or so.

Thanks again.