[docjay]

The thermostat bypasses the radiator when cold, but not the engine. The coolant has to be allowed to flow in order for the hot coolant to fully open the thermostat. Being electronically controlled means there just needs to be a sensor near a known hot spot to trigger flow from the pump.

I’m not familiar with the impeller shroud you mentioned, but I looked it up and the description seems to agree: “This pump includes the shroud and control valve to restrict flow while the engine heats up.”

Whether or not it affects the time required for the heater core to be operational would depend on how they decided to route it, and if the solenoid offers variable positioning. I imagine it is variable, otherwise they’d create thermal shock every time the engine heated up and the pump suddenly started flowing colder coolant through the block, so technically it should be possible to fully replicate the general functioning of the thermostat and heater core. Now that I think about it, it’s most certainly variable and it’s why they didn’t go with a clutch system.

[ErroneousBosh]

It's not variable, it just pulls in and out with a solenoid, either fully surrounding the pump or fully retracted.

I hadn't thought about the thermal shock thing but I did wonder how it could possibly help the coolant warm up if it's not circulating at least through the block. The engine doesn't warm up evenly.

[docjay]

Oh wow, it’s upsetting that it’s not variable. The total system might hold 2x (or more) of the amount of coolant in the engine water jacket. When the coolant around the engine gets up to ~200 degrees and the pump suddenly snaps to 100% it’s going to flood the engine with coolant at ambient temperature. Imagine getting the engine up to operating temperature then dropping it into a swimming pool; even in the kitchen you find out that’s what causes pans to warp and glassware to shatter, and the engine is just a funny shaped pan with bolts.

My only other guess is that it’s not 100% on/off, like maybe a bit is still allowed to flow when “off”, but then it would still need to bring the entire coolant mass up to temperature so I’m not sure how that would be a benefit for faster warmup. Either there’s some clever engineering I’m not seeing, or you’re buying a few points of regulatory compliance for them by needing to replace head bolts and gaskets sooner.