I missed that. The thermostat controls and directs flow through the radiator. I'm 95% sure your #1 problem is that without a thermostat, less coolant is going through your radiator. I wouldn't change the water pump unless you know it's bad. And another flush might really be worth it, flushing through the drain plug in the block and using the correct coolant.

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.