Picked up a 1966 F100 and it has a later model 351W installed. It overheated on the first ride this weekend, it climbed to 240 when I stopped and you could hear the coolant boiling in the top hose area. Bought a new thermostat (found out the old was was in backwards) and I thought that would take care of it. However, I started it up today, left the cap off and turned on the defroster and let it warm up for about 15 minutes in case there was some air in the system after changing out the heater core over the winter. All during the warm up, and for about the first 5 miles, it was sitting at just over 160. After 5 miles it started warming up gradually, 180, 200, 210, 220 If I came to a stop and sat for a minute, it would heat up quickly to about 230, then it would come down to about 210-220 when I drove it about 50 mph.

Does it sound like the radiator is not flowing properly to you guys? The fan and water pump seem to be working ok.

 

I would flush the cooling system and see if that helped. The radiator could be plugged. What is the opening temp for the thermostat you installed?

 

160 degrees.

 

I would check the water pump to make sure it's actually moving the coolant in the system. At 2000 rpm, it should be hauling the mail thru the radiator and should suck the coolant level down as the thermostat opens. Water pumps on these early engines were a known problem child with the impellers pretty much rotting off and not actually pumping coolant like they should. The engine should be equipped with a fan clutch. At full running temp if you move the throttle up to a 2000 rpm fast idle, it should be moving air like a hurricane. The older models moved a LOT of air thru the radiator and it was common when the clutch fully engaged to hear the air roaring thru the radiator. If you're not getting any of that, then you're looking at replacing them. If these seems to be fine, have a shop test the radiator for carbon monoxide. You could have a slight head gasket leak. Another issue is does the engine have a catalytic converter? If yes, have an exhaust shop check it for obstruction. An exhaust that's plugged up will cause overheating. And a rare one but I've had it happen to me, is the intake manifold an aluminum one or cast iron? The intake has exhaust runners in it that run under the carb to keep it from icing in the winter. I've had 2 manifolds where it cracked between the exhaust runner and the actual intake. The exhaust gases will ignite the gas in the intake and as the engine heats up will cause major idling issues. One such manifold had actually coked oil on the bottom of the manifold and turned the cast iron blue from heat. But this will cause idling issues as it heats up. Might also check the timing as that can also cause overheating. If all of the above are not an issue after checking, take it to a radiator shop and have them power reverse flush the system. If at sometime during the life of the truck the system was allowed to go to rust, you can literally fill the bottom of the engine water jackets with rust and major hot spots will happen that cause overall over heating. Reverse power flushing is the only way to clean it out other than engine removal.

 

Thanks for all the info. I hope only one is needed, flushing the radiator!
There are no idling issues so that should cover the intake issue you had.
I'm not discounting the water pump at this point, but I did pull the radiator today and will have the shop go thru that this week. I'll ask them about the carbon monoxide, hopefully that's not it.
I'll post an update as I proceed.

 

Update. I pulled the radiator and took it to a shop. They did a baseline flow test and it passed 11 gpm, and he said it should flow 39 gpm.
They flushed it and tested again and it was up to 26 gpm. After one more aggressive flush it increased to 33 gpm.
Hopefully that will be the end of the issue.

 

If the engine coolant passages aren't plugged up to?

 

We'll find out soon if this took care of it. Keeping my fingers crossed.

 

My first car was a ragged axx 1956 Chevy convertible bought in 1963. I stupidly ran just water in the cooling system for a few months and the radiator got plugged up. I had the radiator boiled at a shop and reinstalled. It plugged again from the rust in the engine block. The engine had a cracked piston, so at that point I pulled the engine and did a complete rebuild, my first engine rebuild at age 19.

 

So far so good. It has been running at about 165 since the radiator flush. I think I should probably get a 180 degree thermostat based on some research, to replace the 160 that the auto parts store said to use in that engine.
Any thoughts on that? 1977 2 bbl stock 351W.

 

I would use a 180. Sounds like your problem is solved! Congratulations!