Well then that's good news!

I wish I had a better answer for you.
It will be getting cold soon and it's really difficult to get that glycol fog of the windshield in winter.

Best of luck.
Look forward to hearing what you figure out.

 

Unfortunately most of the parts stores around me only carry the Spectra Premium heater core, which is what has failed me twice. I just ordered a Pro Source made one which looks to be closer to the OEM core I took out. Hopefully that will work. I also bought a new thermostat and rad cap just a cheap insurance against one of those (even though new) being the culprit.

 

Put a restrictor in the pressure side hose and buy the core from a radiator shop. My local radiator shop checks them first, didn't cost enough difference to make up for the time I spent swapping out the leaky AZ one on my 78.

 

Rickey tested every one of the heater cores I installed to 28psi...
They still blew up in service.

The realization we both came to is that the heater core loop has nothing to do with the thermostat or radiator.
It comes from the intake and goes right back to the pump.

 

What side is the pressure side? The thermostat housing side or the pump side?

 

Um, the thermostat is what's blocking flow *into* the radiator and the pump scavanges cold coolant from the bottom of the rad and forces it through the timing case into the engine block.
In a closed loop system there couldn't be pump pressure, it is acting as a circulator.
Pressure forms because the coolant expands when hot, and that pressure should be equal throughout.

 

"Pressure side" meaning flow feed direction. Does the feed to the core come from the thermostat side or the pump side? I ordered a flow restrictor from a Fox body Mustang, so I want to make sure it goes on the correct side.

 

This right here is the definition of feed and return.
I'm sorry. I don't know how to make it any more clear.

 

Spectra stuff is garbage. I replaced my 16 year old Ford rad with a spectra and it started leaking 6 months later...

 

I was having problems with new heater cores as well. Found a NOS Made in USA copper/brass heater core on ebay for less than $30 shipped.. Haven't had any problems since. Worth a look to see if you can find an old non-aluminum one.

 

There should be a Motorcraft... Yep, Rock:

More Information for MOTORCRAFT HC7

88.79, yes aluminum.

I also recomend using a restrictor from a Fox Mustang in the inlet of the core.

Was the original blown up so bad a competent radiator shop couldn't/wouldn't give it a shot at repair? If not how about a used one & have it tested?

 

Only reason I wanted to make double sure is because the 4.9 doesn't have the boss for the heater line in the intake, it's in the thermostat housing which is bolted to the head, not the intake.

So, just for future readers of this thread, the Fox restrictor (XR3Z-18599-AA) is for a 3/4" heater hose. The hoses on the 4.9 are 5/8". Try as you might, it won't fit. So I ended up getting a copper 1/4" pipe cap and drilled a hole the same diameter as the Ford restrictor. It's a snug fit, but made it into the hose without much effort.

Also, I would not reccomend the Pro Source heater core from Autozone. While the core and end tanks themselves look better made than the spectra, the inlet and outlet pipes are too long. It took way more effort to get them into the heater box than it should have. If this one gives up the ghost, I guess I'll bite the bullet and order the Ford core.

 

I should have thought about the 300 having its intake hanging out in the breeze.
Sorry.

If you're concerned about electrolysis why use a copper restrictor with an aluminum heater core?

 

so are spectra radiators really that bad? and heater cores?

 

I wouldn't say I was worried about it. Just wondering if electrolysis could affect a core in the span of 3-4 weeks. Considering I tested it and it was only 40mA, I'm not too concerned about it now.

Not sure if I got two duds or what, but I tested pressure tested them both after I pulled them out and they both failed in the same exact spot. It was the two middle rows on the upper tank. First one was a small leak, the second one was a larger one.