Many years ago, I was getting barely enough heat coming from my heat vents to tell the difference between heat and just ambient temps. I was maybe 20-21 yrs old. I took my Jeep to a radiator shop to get it fixed. All he did was disconnect the heater hoses from the heater core connections. The he had a homemade contraption he had made. one end connected to a water hose, and he had another inlet that came from his compressor, with a quick connect and a ball valve. Turn on water, when it started coming out of the other core connection, he'd hit the air, all kind of crap blew out. Then repeated that several times, then he switched the connection to the other heater inlet, then again, all kinda crap came out again. he switched it back and forth a few times.
Then he connected the two hoses like what you do when you have a bad core and you bypass it. When it started circulating, the drain valve would not keep up, so he loosened the bottion rad hosee and just took it off and on. We also decided to changed the thermostat end the end we ran water through the thermostat,, top of radiator, and each hose, well one, but tried both . COMPLETELY took off the rad drain, LOTS or junk frrom there, he also shot air in there from thee top. When it was all said and done, only clean water came out from all the orifices. And way back then, he charged me $25! So, just some ideas. But in my experience, I went from luke warm to run you out type heat!
