The radiator guy said it was clogged with BarsLeak, or a similar leak stopper. It took a while to get the heater core flushed out to, and I'm not convinced that the heater core is flowing that well. I have another one, but it's with the AC HVAC box that I bought for when I convert this car to an A/C car.
The block has always flowed fairly clean water through it. Fortunately the issue is resolved.
