I know this has probably come up before, but....
Have a 94 f150 5 litre, air , auto.
I had a small leak in radiator so i did the whole job at once.
Radiator, water pump, themostat, hoses, fluid.
Before working on it had great heat and no problems.
Now after work very low heat ,and my temp gauge goes up to about 80%
then back down then back up to half. then back down.
I have been told i must have some large air bubbles moving around
in the system. I've been told i have to " burp" the system by one guy, and a ford tech told me i have to do that but on a real good incline to try to get the radiator higher than the heater core.
Any other thoughts for the newbee?
Thanks Mark

 

Yup you probably have an air pocket. What I do is run the engine with the rad cap on and start squeezing the upper and lower rad hoses while filling up the rad as the level drops when the engine is hot.

 

Thanks for your imput. I kinda figured this was a common problem.
Just wish it wasn't when it was 10 below!
Any other suggestions welcome for secret fixes.
Thanks again
Mark

 

Just don't let that air pocket stay in there for too long when driving, or you will create a hot spot inside wherever its trapped and possibly warp the block or head.

 

Remove the cap and start the engine. Let it run until it come up to normal operating temp. The T-stat will open and start to circulate coolant. You'll notice the coolant level in the radiator rise and fall. When it fall below the cap opening, refill until you have a constant coolant level. This should get rid of any air bubble in the system.

 

Thanks guys. Still burping and squeezing and filling. Man what a pain in the rump.
I'm starting to think i have a plugged heater core. Is there a valve on these systems
that stop flow to heater core? On my old javelins there is a valve on the rear of the intake manafold that stops the flow when you move the hot cold lever on the dash.
I don't see anything like that on these fords. Does the fluid always flow through the heater core?
Also before i changed everything when i started truck and started driving down road
i would always here a little gurgleing in right side of dash for about a min.
Now i only here a tiny gurgle when i start to go in the morn.
One more thing, is the wire harness connected to the metal tube behind the thermostat the temp gauge senser?
Thanks
Mark

 

There is no shut off to the heater core unless you were to add a bypass, coolant always flows through it. If you have a plugged heater core, a good way to tell would be to feel the hoses when the truck is warmed up. If one is real hot and the other is cooler, good sign its plugged and would need replacing.

Also the temp sensor on the thermostat housing I believe is for the computer on the 5.0L

 

Thanks, I think i have the bubbles and temp spikes under control, but i'm just getting luke warm air flowing into cab, Before i had to open the windows cause it was so hot in there. Checked some of the old theads and it looks like easy change out behind glove box door for core.
Mark