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Not M37 related, but interesting anyway:

My granddaughter has a '87 Thunderbird which blew a heater hose. She wisely pulled off the highway and called for assistance. When her step-dad and I got there to get her back on the road, we simply cut the end off the ruptured hose and tried to slip it back over the nipple on the heater core. No go! A closer inspection of the hose end with a flashlight revealed a 5/16" nut jammed into the hose. It was a snug fit, so someone had purposely stuffed it in far enough to get the hose on the nipple. Why? Who the heck knows!

Perhaps to restrict the flow through the heater core? I dunno....

Sounds like either wrong size hose, or wrong size nipple, and Goober tried to make it fit instead of doing it the right way......

The hose was the correct size, so we can only assume that it was a measure "designed" to restrict the flow of water. Dunno why they'd want to do that, but it definately resulted in higher pressure within the hose and caused it to rupture.

That wasn't OEM on a 87 T-Bird?

Wasn't there an issue with some Ford heater cores blowing out due to weak solder joints? Seems like people were putting flow restrictors on some model...might be that one.

Refit is correct. Ford heater cores from the 80s and early 90s were notorious for rupturing, and since it requires removing the dash and column to fix it, an easy way to help preserve the life is to put something in the line to restrict the flow and lower the pressure in the core.