OK, I need some suggestions. Assembled a 79 400, all new stuff pretty much. I start it up, and it heats up surprisingly quickly to 3/4 gauge. I ran it for a few minutes at a time, thinking that maybe an air pocket was around the thermostat or something, but it was consistent. Could see almost no flow in the radiator, and the top hose seemed to be hot by the engine, and cooler away from it. Took out the thermostat, and I get lots of visible flow in the rad., and it runs 1/4 gage (seems high for no thermostat). Repl the stat with new, same story. Thought that head gaskets may be reversed (an earlier thread), but that does not seem to be the case (I can check with a wire on one side, and I noticed that the gaskets have a tab that protrudes visibly near the front corner if installed correctly). I took off the water pump and flushed water through the block on both sides, and it comes out the top OK. Once when it ran just over 3/4 gage, I tried to restart it and it cranked slowly, like it was very hot (great way to break it in, I know).
The pump is now off, and I'm fishing for advice. During the rebuild, I replaced the freeze plugs (off during vatting), and scraped a pile of dirt out of one corner of the jacket (the engine had sat and vermin may have nested there). .040 over, and a new sending unit (I may try putting in the old one, but the flow problem and slow cranking seem to vindicate it).
Oil pressure is great.
Suggestions? Thanks!

 

I'd replace that sending unit with the old if it was working....also maybe the timings to high? Had them run hot with me if I ran it to high (right on the ragged edge, also make it crank slow when hot). I take my thermostats and drill a 1/8 hole in them to avoid air or steam pockets....heater doesnt work as well during the winter but with a new motor it gives a little peace of mind. Also are you using the old hoses? if so check the lower hose for the sping in it, if its not there the hose will suck together and stop the water flow. Just some ideas to try. Later Whit PS if the tabs are showing I'd bet the head gaskets are correct

 

When I boughtn my 79 Bronco I put a new 195 thermostat in it to make better heat for winter. It worked great. Then summer came. It ran hot very hot. It did similar things yours is doing. So I recently took out the 195 and put in a 185. What a difference 10 degrees makes. I do not have heat as fast but it will still roast you out and no more running hot.

 

Thanks for the input. I may have a combination of problems. I like the idea of a small hole in the stat; I bet it has little effect on the heat. All new hoses, btw. Tonight I will reassemble it, maybe with a cooler thermostat (although that shouldn't be the problem, thinking logically), and try trading out the old sending unit. The timing may be off (I got it roughly there, and planned on using spark knock to finish). Maybe between the high friction of a fresh rebuild, the 195 stat, a sending unit that reads high, and timing that's off, it appears to run warmer than it really is. The radiator was decent before, and I flushed it out well when off, so it should not be an issue. I'll post what happened by the end of the week.
Thanks!

 

Here's what I did:
Put in a new 180 deg thermostst with a .090 hole drilled in it.
Put it all back together, and it's fine!? Runs at about 1/4-1/3 gauge, and heated up reasonably slowly.
I think the problem may have been trapped air, exacerbated by the fact that it was completely dry, including a new heater control valve that would be tight and dry. Thanks for the drilled hole idea, broncoman, that may have been it.
If I get bored, I may try a 195 stat again, maybe with a hole, if my curiosity exceeds my free time.
Thanks for the help!
sfh

 

I recently rebuilt a 78 400 and had the same problem. It turned out to be the ford flex fan. I just coudnt keep it cool especailly when idling. I bought a new clucth and fan and walla problem solved. Just an idea you might want to look into. Im not sure why the flex fan does not cool on a new rebuild.
Let me know what happens.
hotdog2000

 

Air pockets can be a pain. Especially if the thermostat had no hole at all. There is usually a very small hole to aleviate air pockets. I've seen motors go quickly to 280 and then pull right back to 120 as soon as that thermostat opens. I've never enjoyed shocking a motor that way. All you can do short of rigging an air bleed at the manifold somewhere is to fill up painfully slow and hope for the best. She'll spike on start-up
and then pull back. That big hole in your thermostat should alleviate any air pockets alright but you want that motor to warm up quickly. So you're OK as long as it warms up normally and not
too slowly especially in very cold weather.