Thank you. There's so much misinformation about cooling systems floating around automotive forums. Nice to see truth.
Technically true, but the "draw" (I'd have said "inlet" or "suction" side)
SHOULD be the already-cooled fluid coming directly from the radiator.
Water pumps
can cavitate, though. I think it has more to do with impeller speed and inlet
restriction rather than inlet
temperature.
Similarly, when there's a problem with the lower radiator hose collapsing, most folks say to shove a "spring" inside to "support" the lower hose. I say to check the radiator for restriction. If the lower hose collapses, it's because you're pumping water out of the hose at the water pump end, faster than it can re-fill from the radiator side.
Propylene glycol (PG) anti freeze is popular with the Eco-sensitive; I've used it too. Doesn't poison dogs or squirrels who might drink a little out of the coolant drainpan left unattended too long. I figure it's better to appropriately contain 'n' dispose of the waste anti-freeze in a timely manner. But like I said, I've used the stuff and it worked OK. Been a long time...
The PG antifreeze doesn't
have to have anything special in the cooling system; it is just a little "thicker" than ethelyne glycol; and doesn't have quite the freeze protection. You'd need a different freeze-protection tester than Ethylene glycol.
"High flow" is very welcome...but only when the heat load demands it. The whole point of a thermostat is to choke-off coolant flow to make the cooling system much less efficient, so the engine warms-up quickly and stays at a reasonably-steady temperature. This is why engines operated at idle or cruise should run within a few degrees of the thermostat rated temperature; if the engine is more than 20-ish degrees above the thermostat rating, it's lost control of engine temp. Of course, some of that depends on when the fan(s) are activated--GM often doesn't turn on an electric fan until 220 degrees or so. The second electric fan may not come on until 230. If the cooling system is running way hot at idle or cruise, it's got no
reserve capacity for when you're dragging a trailer up the mountain, or other heavy-throttle use. THAT is when the thermostat should be WFO, and the engine coolant temp may climb some.
The "big deal" with having a restrictor in the thermostat housing--either an actual thermostat, or a restrictor disc--comes from the older, top-to-bottom flow radiators. UNLIKE a typical cross-flow radiator, the pressure cap is on the
inlet side, ahead of any restriction presented by the coolant tubes in the radiator. Having radiator-cap pressure, PLUS water pump pressure (especially at high water pump speed) that isn't moderated by the restriction, will overpressurize the radiator cap, causing it to release pressure and therefore loss of coolant. Then the system is low on coolant, so the engine overheats.
A cross-flow radiator has the pressure cap on the
outlet side, so it maintains cap pressure despite water pump suction, leading to higher overall pressure within the engine. Cross-flow radiators are way better than vertical-flow radiators for this reason. And then GM starts building vertical-flow radiators after decades of cross-flows, for the GMT360/370 Trailblazer/Envoy series of vehicles.