I have a '79 400 that has developed an overheating situation. The story goes something like this: Earlier this summer, I rebuilt the entire cooling system. New water pump, new hoses, flushed and boiled out the radiator, new 16 lb radiator cap, new thermostat. I started driving on the new system, put about 150 miles on it in midsummer weather (80-85 degrees F), everything seemed to be pretty good. A couple of nights ago, I took it out in the evening (72 degrees F), not expecting any problems. I was out for maybe 10 minutes and smelled hot antifreeze, and found her boiling out of the coolant catch can. I managed to get her home with some coolant left in the radiator, and I thought that maybe I had goofed and not gotten the radiator cap back on tightly the last time I topped her up with coolant. So I refilled her this morning, put the cap back on and verified that it was secure, and took her out. Once again, I was home in 10 minutes. One thing I noticed is that on both trips, when I got home and popped open the hood, the water was quiet and stable in the catch can; it's only when I shut the motor down that it started to boil over. That, to me, seems like it must be a pressurization problem. I know that it is building and maintaining at least some pressure because when the thermostat opens, the upper radiator hose is firm (and obviously it wouldn't open the radiator cap if there wasn't pressure). I'm open to suggestions as to what the problem might be, but what I really want to know is, what are the things that I can check/test to help me determine the root cause? Thanks for your time.

Edit to add: I just went out and checked it. It's been half an hour since I shut it down, and it sucked all the coolant out of the catch can and back into the radiator. Could it possibly be a head gasket? Though that would seem to make less sense if it's only boiling over when I shut it down...

 

I'm trying to chase down overheating issues with mine as well. Here's a link to my thread:
https://www.ford-trucks.com/forums/1...erheating.html
Lots of good suggestions there - unfortunately, none solved my problem, but maybe it'll help out.

 

Clutch fan worn out?

 

Thanks for posting this...

I just realized that some of my overheating issues that I'm having may be due to a faulty radiator cap.

I just about overheated last friday (same story as you), but I spilled ZERO coolant down onto the ground... meaning my radiator cap is over-pressurizing the system? Possibly?

over.

 

Check for a backwards head gasket. No such thing as over pressurizing the system. If one gasket is backwards it'll do as you describe. The coolant gets trapped in that cylinder bank and will flash to steam when it gets hot enough to boil. Then it backfires through the waterpump into the radiator. Everything will seem normal until that point including the temps.

 

As this problem recently developed (and I haven't touched the gaskets), after running for 3 years, that seems unlikely. In the event, I think I found it; after the last shutdown, the radiator cap retained traces of a brownish-green murky residue... oil in the water. Blown head gasket (I hope; I'm praying I didn't crack a head or the block). Time to tear her down, I guess.

 

If you have a blown gasket, then there would be pressure in the cooling system while running with the cap off.