[lhj]

This problem has happened twice now since it has warmed up. After driving around 20 miles the needle on my temperature gauge goes up to ¾ . It's usually just under ½. If I slide the heater temperature switch all the way to hot and I crank up the fan, it vents enough heat to cool the motor. The gauge goes back down to normal. If I stop the fan it heats up again. If I let the motor cool down for 15 minutes it wont heat up again until I drive another 10 miles or so.

I checked the coolant level and it's OK and the right mix. There are no apparent leaks. The fan seems to be working OK. The water pump shows no signs of leaking.

I replaced the radiator cap and the thermostat.

I also bled the system.

The radiator is old and shows some rust and corrosion.

Any suggestions where I should start first?

Could this be the coolant temperature sensor?

Has anyone had this problem?

Thanks in advance for any help.