[Cathar]

Mainly to Bill.

Can't argue that viscosity increases, but as pointed out in private emails, the size of the increase is probably important.

The White Water's flow resistance using 25C water already allows the block when installed in a full system to offer a level of back-pressure that sits squarely in the middle of most pump's duty points which is true for Eheim 1046, 1048, Iwaki MD20-RZ, Iwaki MD30-RZ. For the Eheim 1250 the block+heater-core pushes back against pump at about 80% of the pump's peak head, which is a little high, but still on the edge of where the pump could be stated to still be running efficiently.

I personally would've thought that the White Water would perhaps fare better as viscosity is increased. Just some hand-waving hypothesis here, so definitely just discussing, not stating anything.

The jet impingement pretty much forces all of the coolant to be closest to the heat, chilling the walls as it goes down. No matter what, the coolant is close to the heat, and even if jet impingement loses effectiveness, the coolant is still affecting the fin walls.

My feeling is that with an open chambered design like the MCW-462, that here the "thick" flow of jet impingement will suffer. As viscosity is increased, less of the coolant is likely to reach the base-plate, and instead will move out into the open chamber where it touches nothing important for cooling.

Thinking here of pouring honey from a jar into a glass vs pouring water. Pouring honey results in nothing reaching the bottom of the glass it just stacks on top, but pouring water has the flow hitting the bottom of the glass with ease. Now I know we're not pouring honey, but this just serves to highlight where I'm going with this on a reduced, (but perhaps still significant?) scale?

Are my thoughts somewhat on the right track?

Is the increased viscosity causing a lower flow rate (how much lower? 10%? 20%) offset by the losses that an open-chamber design will incur as less of the coolant reaches where it has to? What effect is the decreased flow rate having on the block's performance? How much effect is the "stacking" effect having on the open-chamber design, coupled with its decreased flow rate as well?