Heater core went... but could I have caused it?
 

Short story shorter - took my '86 F250 / 351 4x4 down the road about 2 miles to give her a weekly ride and drink of gas.

At the pump I noticed the windshield fogging up something serious - pop the hood and see antifreeze pissing out from under the heater core. This seems normal, nothing to worry about (aside from some $$.)

OK - but I'm new to this girl, and last week I hooked up the PVS controlling the distributor advance like this:
top (furthest from thread) : manifold
center - to dizzy advance
bottom (at threads) : carb spark advance

Reason I hooked it up this way way to allow for cold start via manifold advance then normal operation under ported vac.

Turns out the line from heater core connects right next to this PVS.

Did I somehow cause an overheat condition?

Does anyone else hook up the PVS like this, or should I just try straight ported OR straight manifold right to the dizzy?

Thanks
-CV

Some of the PVS's are hooked that way from the factory, so I wouldnt worry to much about that causing the heater core to blow.

It was possibly just it's time to blow.

I just replaced the HC in my '85. It was the original. The nozzles were corroded and coolant was not flowing correctly. When you replace your HC lubricate those nozzles so the heater hoses slide on nice and easy. That metal is soft, you have to be gentle with it.

The heater core header where the pipes are soldered is very delicate. Always cut the hoses off the heater core pipes when replacing them, twisting on the old hose will break or weaken the heater core every time. So if you just replaced the heater hoses recently, that's a good reason for it to blow.

I am also reading you were doing some engine work. If you happened to have leaned against one of the heater hoses near where they hook to the heater core, this can also cause the core to leak, been there done that.

Once you get the heater core out, if you find the leak right around where the pipe goes into the heater core, strain on the pipe was certainly the cause. You can clean this up and actually re-solder this if you are inclined to do so and have the soldering tools.