In the last 6 months I've had 3 heater cores go out in my 89 7.3 idi, The original and 2 aftermarket Spectra cores. I checked for electrolysis with a volt meter, showed 0.0.95-0.1 well below the 0.3 minimum. Its got a 7lb stant radiator cap, not sure what else to check. The last core blew and I found a pinhole in a tube.

 

Maybe the radiator cap is failing, and allowing too much pressure in the heater core circuit.

 

I stopped having frequent heater core failures (6-9 months) when I stopped buying cheap China aluminum cores. Buy a brass Motorcraft heater core and it'll last a long time.

 

I just ordered a new motorcraft aluminum heater core, original aluminum one lasted 28 years. Gonna change the coolant and the additive(vc-8), is there anything else I should do? Thought about hooking a gauge up between the heater hoses and checking for excessive pressure.

 

^^^this^^^
the cheap china replacement cores are paper thin. get a made in USA core and it will last 30 years like the original did.

 

If your old core was aluminum it was not original. OE/Motorcraft heater cores have always been heavy brass/copper. As of a couple years ago they still were, it would be quite unfortunate if they stopped making them and sell rebadged China aluminum now.

 

From what all I see, 80-86 is brass,87+ is aluminum, it had Ford on it, I'll get a pic when I get home

 

That's possible. I didn't realize we were talking about a new truck.

 

Here's the core

 

A faulty radiator cap and cheap cores was the issue.

 

Good to see you figured it out. Also, thanks for posting the conclusion to the forum so that future users can learn from your investigation.

 

I wish the aftermarket cores were brass/copper, seems like they would last a lot better but instead there made out of my neighbors old beer cans..

 

So the brass Ford ones are around $90, hc-1 and hc-3, the aluminum core is hc-7 and the same price. Spectra is cheaper, but available about anywhere.

 

A quick search on eBay and I found the hc-1 for 50-60$

Thanks a ton for the numbers, I love part numbers and try to keep as many as I can find around.

 

Glad you figured it out, the brass cores are a heckuva lot better than the aluminum ones. One other thing that will help, is soldering a ground wire to the core and running that to chassis ground (firewall works well). It will help prevent damage from electrolysis. You can also add a radiator cap that has a sacrificial anode to help prevent it as well.