This one has me stumped.

I got a 1992 Ford Explorer 4.0 4x4 and automatic.

I replaced my intake manifold gasket (upper and lower) this weekend
and when we got everything back together, the engine ran fine, no
leaks, sounded good. But when we started it up the temp gauge was way
over. Then we finished adding more coolant once the engine sucked more
into it. Still high, but not all the way to the "H" on the gauge. So
we took it out on the highway through the city and then onto the
freeway and up a small hill on the interstate. Everything ran
consistantly with the gauge right at the "O" in the "normal" on the
gauge. I go back through town and when I put on the brakes and come to
a complete stop, the gauge raises up nearly to the "H" and then
proceeds to drop back down to midway on the gauge. It takes about 15
seconds for it to rise and then drop.

The coolant was good. I double checked for leaks. The top radiator
hose was pressurized and hot. The radiator spit back a bit of the
coolant into the overlow can.

Right now we're thinking it is probably a wire that got pulled to hard
and might be grounded near a brake wire. Or it is possibly a faulty
temp sending unit or maybe even a bad guage.

Any ideas? You guys really helped me out with my pinging. After
changing the intake gaskets, cleaning the carbon off with some SeaFoam
cleaner and cleaning the MAF sensor, no more ping.

Thanks in advance for the assistance.