Air Trapped in Block Coolant?

[jec]

Well, I've always relied upon the "Board" for hard to get parts and/or information so let's see what kinda tips you'all have for a strange problem with my Coolant System.

This is on my restored '72 Longorn with big-block and 4 core radiator. The truck originally had air conditioning, however, I decided to build with an air delete option. This was an 8 year restoration project that I just completed this spring. I have had it out to a couple shows and it's been alot of fun.

My problem is that after the truck has been running and it's at normal temperature (as verified by factory gauge in dash), upon shutting it off, it sounds like the coolant is boiling in the block. The sound lasts for about 30 seconds and it dissipates. Now, I know what it sounds like but I'm pretty sure it's not overheated.

This happens after just idling in garage for 20 minutes or driving around just the same. Here's what I know.......I can see coolant flowing thru radiator with cap removed. Both upper and lower radiator hoses are hot. The thermostat seems to be fine. I have a factory clutch fan and shroud in place and there is a strong pull of air by the fan moving from the grille toward the engine.............The temp gauge moves just about 1/3 of the way over just as it always did before I restored the truck. Same radiator, water pump, gauge, and sending unit as before I restored the truck.........I don't have the heater hoses hooked up at all, they are capped off.

Any ideas???? Seems like there is just air trapped in coolant system within block but I don't remember ever having this problem on any of my other vehicles over the last 40 years.

Anybody know what to look for????

Thanks,
Longhorn John