Bypassing the pump shouldn't hurt anything, especially since you're bypassing the heater core altogether, and since since you're bypassing the heater core, engine temperatures should act the same as if you were running with the heater off.

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Streetside: 1987 Mercedes 300E Petrol Blue/Green
2014 Ford Mustang Grabber Blue
1999 Ford Ranger Green

Dockside: 1968 Eltro 17
1985 Silverton 34C