Here is a stumper...

[dragonlovestrucks]

77 C10 Big 10 Longbed. 350.

Engine runs a little hot, coolant starts boiling over.

After letting it cool down, and re-starting it, the back left wheel locks up.

Give it a few minutes, say under an hour, more than 10, but its more art than science, the wheel unlocks.

What would you look for and where would you start?

[mongocanfly]

I'm not sure i understand what the overheated engine has to do with wheels locking up..
but start with why the engine is overheated...water pump, radiator, coolant level ,fan clutch should all be checked
if the wheel is locking up that's probably a brake issue...check brake adj, brake pads, drums, and all brake mechanism behind the drum

[LeesTruk]

Seeing's how the rt. and lh. rear wheels are fed from a common junction, and only the lh. is locking, I'd pull the left brake drum and see what's going on inside. Would venture a guess that the left wheel cylinder is the culprit

[dragonlovestrucks]

I'm not sure the link either - it would be crazy to think that these are related somehow, yet the consistent timing of it happens.

I haven't pulled the left drum yet, but I also considered it would be the wheel cylinder. What boggles my mind is that it just "resets" back to drivable condition given enough time.

Coolant level is filled up, but then boils into reservoir. Fan works.

What's the best way to check the water pump? Just replace it?

[jocko]

Agree - you have two separate problems.
Overheating - feel your upper radiator hose - i.e. ensure your thermostat is opening. If lucky, it's just that. You can remove it and test it in boiling water to ensure it's opening in roughly the correct temp range. Or just replace it because it's likely ancient anyway. Any coolant leaks around the water pump? Look around the weep hole on the pump. Air gap in coolant can cause overheating also. With belt off, check for fan being wobbly,(bad water pump bearing). Also check/confirm that your fan is working correctly (if you have a clutch fan).

Brakes - you'll have to remove the drum and inspect for something broken or malfunctioning wheel cylinder. Or better yet, when stuff like this happens, it's probably time for a full brake job anyway. Go that route and maybe you'll find the culprit along the way. Take cell or camera pics of old brake assembly (both sides) BEFORE you tear it down - lots of close ups so you can see how all the springs etc overlap and what they connect to. Easy job, but easier if you plan ahead.

[Dead Parrot]

Does the exhaust pass near the left rear brake line? Possible the line is mostly plugged and seals shut when hot and opens when cool.

Proper mix of antifreeze and water? Near pure water can boil in a normally operating motor with a 195 thermostat. The t-stat temp is the temp it starts to open at, not the normal operating temp. Normal operating temp is 10~20* hotter then start to open temp.

If you have or can borrow a laser temp gizmo, check for hot and cold spots in the radiator. Possible it is mostly plugged. Use a spray nozzle and clean the air passages in the radiator. A couple decades of mud and dead bugs can limit proper air flow.

[mongocanfly]

well I thought had thermostat in my 1st reply but looks like I forgot..but jocko posted it....check bottom radiator hose and make sure it isn't getting sucked flat