I have a 1977 f100 with a speed density 5.0 I felt that this section would be better to post in. It has an aluminum radiator. A new water pump (when I put the motor in) 4000k ago. And a 195 degree thermostat. I added ac and it started overheating but only when I was driving and the ac on. I could leave it in the drive way and the temperature would not climb even with the ac on in the middle of the day. So I flushed the radiator yesterday and put a 180 degree thermostat in and water wetter. Thought everything was fine and it overheated on the way home from work on the highway. So I turned the ac off and the temperature wouldn't drop. Made it home and let the fan cool the radiator down. I don't think it's the head gasket cause when the engine is running they're no bubbles in the radiator. Someone please help its my daily driver

 

What kind of mixture are you putting in? Id imagine 50-50 since you did the engine swap. Have to ask lol. How big of a condenser did you put in front of rad? Is it blocking too much maybe? Is the fan the original fan for the engine? Is all the air berped from system?

 

So the engine has an EFI set up now?

 

It's a 50/50 leaning more to concentrated coolant. Btw 20"by 20" condenser. The original
Fan is a Mechanical I swapped to an electric Taurus fan. I believe all air is berped out i i squeezed upper and lower hoses multiple times While engine was running and added coolant. I have a feeling lower radiator hose is collapsing on the freeway but at the same time I fear the worst being a head gasket or head problem.

 

If i remember right, they were smaller comdensers. So maybe too much heat in condenser, and with more blockage over rad. The way i berp a system is i have rad cap off, and run the truck to temp. Maybe it could help? And are you sure the fan is pulling air? I also believe that they are supposed ti be puller fans not pusher.

 

I have berped the system completely with rad cap off. The fan is pulling air. I can f el the cool air being pulled
Form the front and hot air behind the fan. Pulling hard too

 

So, if i understand right, a/c on yiu start overheating. A/c off is ok?

 

A/c in the driveway all day long and i won't overheat. Driving with a/c on on on the interstatr 10-15 min and it over heates. Maybe my lower radiator hose is compressing.

 

Is this engine EFI? How are the accessories run with a serpentine belt set up?

 

It's an efi motor. Driverside is alternator power steering pump and water pump that has one belt and then passenger side is ac compressor, idler pulley and the smog pump but I replaced it with an eliminator pulley

 

Im starting tl wonder maybe your hose is collapsing under load...kinda uncommon... at least in my personal experience.

 

That's what I'm starting to think. I had to use two hoses to make one for the lower. I'd like to replace with a metal one but it's Sunday and I'm unsure of who sells them. Or maybe a spring?

 

Even with a metal one you will still have some hose so the engine can flex from rad. And as far as who might sell a.metal one anyways...i have never even looked so i dont have that answer. I know semi trucks run springs inside certain hoses so that would.be the direction i would go.

 

Is the water pump turning in the correct direction ?

Some people installed non EFI water pumps on EFI

set up engines causing conditions like yours.

Idling vs. load are very important factors in the issue.

Double check the pump.

 

What is "overheating" to you? It's normal for the engine to run a little warmer with the AC on. How big is the radiator?