I hope I can describe this well enough.
I have a 78 F100 with 351m, 84K miles. Had issues with a broken plug and eventually had to have heads pulled and lots of little things fixed (done at a machine shop, beyond my humble skills): heads were resurfaced and reconditioned, replaced some leaking freeze plugs, put in a new radiator and water pump we repaired. Had to put in new temp sensor.

Anyhow, got it back earlier this week and it sounds and runs great. Except as it heats up, it starts to make a knocking sound. There's also what sounds like boiling water and air bubbles in the block itself. The temp gauge reads right in the normal range, the radiator is warm but not too bad. it fills the reservoir as it cools, then it goes back to level. It gets more intense for about 2-5 minutes after I shut it off, then it quiets down alot.

No fluid or strange vapors in the exhaust. The power is pretty good (except going up an incline when it cuts out: needs carb rebuild).

A friend of mine thinks its just air in the cooling system that needs to work its way out. I've put about 50 miles on it in short trips so far.

Any ideas?

I plan to take it back by the shop once the holidays settle out.

 

It sounds to me like the head gaskets are on backwards. It's an easy mistake to make. Or possibly the thermostat in backwards.

 

Pull the spark plugs and check them

 

Could be as simple as just a bad radiator cap. Before tearing into the engine or doing anything expensive, get a new radiator cap and put it on... May help, may not... but for $5 and 30 seconds worth of work, i cant think of a better place to start.

 

new radiator and cap already...

 

I will try the art of reading spark plugs tomorrow.

 

Yep! Sounds like head gasket on backwards. Feel under front of head, an look, you should have some head gasket sticking out towards radiator. Good Luck

 

Here is the driver's side gasket photos and spark plug


the plug

 

Here are some of the passenger side

 

The passenger side looks dry and "normal". The driver's looks like its got coolant on it?

 

i didn't see the head gasket on your pics. And on the first pic have you notice your belt alignement ? The washer should be behind the power steering bracket or have a spacer.

 

the drivers side pulgs look more like soaked on oil, have you tried the texture with your fingers?

 

It surprisingly difficult to get a good head shot.

I'll do some more tinkering tomorrow.

 

I'd run it and when it pushes out the coolant into the overflow....break the vacuum in the radiator so that it doesn't pull it back in and run it a bit low....i have a 429 that runs hot and pushes coolant out when full.... then runs fine. might not be the head gasket and thats a bit of a pain if it is.

 

Tried breaking the seal on the radiator, just a lot of coolant everywhere, the noise may be a little quieter but still knocking.
Got a few shots of the head, not much to see
Basically, the driver's side has a little blue gasket showing. On the passenger side, I can see bare engine block and no gasket (both on radiator side, didn't try to contort to get rear view.

Below is the only shot of passenger side. All the rest are driver side



A few more shots are in the gallery.