Just be sure you use something designed to have hot coolant under pressure behind it. Most use large vacuum caps and you'll see them deteriorate quite quickly. That's why I usually use a short piece of heater hose clamped onto the nipple, and then clamp the right size bolt into the hose.
As I recall the inlet to the t'stat housing has nothing to do with the heater. It's a bypass hose isn't it? Keeps the water pump from deadheading when the t'stat is closed. I'd want a real clear understanding of the control mechanism for the electric pump before I blocked off the bypass.
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