Engine overheating

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.

i have the 3.3l engine and mine was doing that same thing so i changed the water pump and thermostat but it didnt stop it. i finally found a hose that was cracked i think it bypasses the thermostat or something like that but after i replaced it there was no problem. it was a little hard to get to though. i think it was a peice of 5/8 hose about 6 inches long and i had to remove the a/c compressor to get to it.

With corrosion on the outside of your radiator, I'd be looking to the inside as cause. I've seen several threads (and worked on several vehicles) that had cooling problems, once it got warmer, due to a partially clogged radiator. Since everything else looks good, I'd consider replacing the radiator.


-edit- Before you do that, when the vehicle is cold, remove the radiator cap and start it up. Drive for a bit or idle until it gets warm. Watch inside the radiator for some water flowing every once and awhile, as the thermostat opens up. If the water is flowing, then the problem isn't the pump or thermostat.

One option short of buying a new radiator is to remove it and take it to a radiator shop to have them reverse flush it with compressed air and solvents. Call a shop and get the details.