I have a 1976 F350 w/390. I just put in a rebuilt 390 and I am getting the same problem I had with my other engine. At idle the engine temp stays cool. When I drive down the road on the freeway, temp goes up and gets real hot. Slow down and the temp comes down. It is using the same clutch fan as the old engine. I wonder if it is the fan or is my radiator blocked somewhere and not allowing enough water through. Is there a way to check my radiator with out taking it to a shop? Or checking the clutch fan? Thanks in advance for any help.

 

Andy, Since your engine is doing things in reverse, I am wondering if you have a bad guage, or timing could be off. Have you shut the engine down to hear it boiling or steaming?

John
jowilker
[link:www.ford-trucks.net/users/jowilker|Club FTE since 01 01] My FTE Page

[link:www.ford-trucks.net/users/jowilker/NCFTE.html|NC Truck Owners] NC Ford Truck owners group

66F100s Rule
In the cool still quite of night you can hear chevies rusting away.

 

At highway speeds a fan does more to block air than let it flow through, that's why they have clutch fans is because after a certain speed the fan isn't doing anything but robbing power from the engine. The fan isn't sucking air at 60mph by 2000 RPM. I'd agree with John and check your timing.

 

John, It is boiling when I turn the engine off. The radiator is very hot. When I timed the engine I used the timing marks and a vacum guage. I timed it by getting the highest vacume reading I could with out the engine pinging. Should I back off the timing alittle? The truck seems to run good besides the hot reading. It did the same thing with the old engine.

 

I would put the radiator and water pump as susspect items if you already didnt replace the water pump take you radiator out and stick a garden hose in the top inlet the water should pour out the outlet on the bottom as fast as you are putting it in if it squirts out the top and flows slowly out the bottom i would say your radiator is clogged, just my 2 cents

 

[font size="3" color="#191979"]
I agree with otto, it could be a restricted radiator. I am not sure about the water pump, but another thing to consider is the thermostat. Sometimes it's those simple things...

Art

 

Back flush radiator with water hose,the water/coolant ratio no more than 50-50, timing no more than 12 degrees. **with engine off**, fan should spin with a little resistance. Drop thermostat in a glass of cold water, then in hot water to see if it opens.
when engine is cold, open radiator cap , start engine, let it warm enough to open thermostat, you should see the water foaming and moving letting you know that the water pump is doing its thing..
https://www.ford-trucks.com/dcforum/User_files/3aa82f3f7f502469.gif https://www.ford-trucks.com/dcforum/User_files/3a9df0394b631ce6.gif







77'FORD F150 XLT 400

 

Make sure there is a spring in the lower radiator hose too. The
pump can suck the hose shut at freeway speed.