Ford F150 - Temperature gauge fluctuates.

I accidentally posted this in the pre 97 forum so forgive the double post.

I have a 99 F150 4.2 V6. On a about 3 occasions, very randomly, from early last week to yesterday, the Temperature gauge will jump to hot and the temperature light will come on.

The first occasion I had just pulled onto the road. So I knew the truck couldn't be hot. It had only been running maybe 3 minutes. I pulled to a parking lot and turn the ignition off, restarted and it was fine.

Two days later, it was around 98°, the same thing happened and then went back to normal then did the same thing twice more. I pulled over and touched my upper radiator hose, warm but not hot at all.

I didn't get a chance to research the issue over the weekend, and didn't drive my truck anyway. Yesterday the same thing happens. 78° at the time. The temperature slowly rose and lowered maybe 6 times on the way home. Again I check the hose with my hand and not overly hot to the touch.

The gauge never drops below normal ranges, just hot to normal.

So, I figure, thermostat, a controller/regulator of some sort or the guage/dash.

Which is best to check first or would I be wise to check something else?

You didn't say if you checked your antifreeze level. Might be an air pocket in the system that needs to be released out. Some one else can correct me or give instructions on how to release air out of the system. Air in the system does not allow the water pump to pump the antifreeze through the system.

Yes.. Definitely check your anti freeze... Make sure when the coolant is up to the proper line on the overflow tank when the engine is cold..

One other suggestion: - Check your temperature sender... (It's on the intake to the left of the upper radiator hose). Make sure the connector is properly seated. Unplug it and check for corrosion on the contacts.

If you have access to a scan tool, you can read the temperature with that (it uses a different temperature sensor than the dash guage).. Compare the reading with the dash guage. If the scan tool isn't changing, then the fault isn't with the general cooling system.