Ford 302 rapid temperature rise at idle

[UKjohnnycobra]

Thanks again, all. It may be a couple of days before I can test these ideas and post pics as I will be travelling for a couple of days. I'll bump this thread later.

[DAVID GAGNARD]

Originally Posted by UKjohnnycobra

Thanks again, all. It may be a couple of days before I can test these ideas and post pics as I will be travelling for a couple of days. I'll bump this thread later.

If you have NO fan shroud at all, that is 95% of your problem.......at speed, air is forced thru the radiator, at idle,only the fans will pull air thru the radiator and without a shroud, they are operating at maybe 50% capacity......

Your pulley sizes are fine,being it runs at the temp it does on at speed, tells me your cooling system is fine....you just don't enough air coming thru at idle without a shrouded fan........

at idle,get out of the car, light a cigarette, put it in front of the radiator and see how much smoke is pulled thru, then put it on the side of the radiator and see how much smoke is going around the radiator instead of thru it, you may be suprised.....the fans will pull the air from on the path of the least resistance, which without a good fitting shroud, it will come from around the raditor instead of thru it.......
David

[SoTxButler]

I had this problem with a car that had a 351 in it. As soon as the car started to move, the temp would start down and then up again as it came to an idle.

Every time I opened the hood, the fan was running...so I never thought to check to see when the fan came on.

After changing the thermostat a second time, I installed a mechanical gauge and was watching the car idle and because I was watching the mechanical gauge, I noticed that the fan didn't turn on until after the temp went past 200 degrees.

I checked the thermistor in the radiator and found it to be defective, it was working and running the fan, but too late. So, air flow cooled while rolling and temperature rose while idling and the fan was turning. I installed a fan controller with a probe for the radiator and set it to turn on the fan at 180 and voila...fan starting turning at the right temperature and no more spiking temperatures at idle or slow speeds.

Check to see what temperature the fan starts running.

[Rick 427 Cobra]

Had a friend with the same issues. We looked at EVERYTHING. It turned out to be the water pump. Some rebuilts come with an impeller that looks like it came off an alternator. Cheesy stamped steel thing. Replaced it with a rebuilt with an original style cast iron impeller and all was good. Just not enough flow at low rpm.
Good luck