ntsqd wrote: ↑Fri Aug 25, 2023 4:26 pm
What I've found with the high flow t-stats is that they don't have as much restriction to coolant flow. That's obvious, what isn't obvious is that a good coolant pump can generate well above cap pressure inside the block. One guy on Classic Broncos did some experiments and it's been a while since I read that thread, but what I recall is that at high RPM it can be above 40 psi. This makes local hot-spots in the coolant jacket much less likely to boil the coolant.
When you reduce the restriction to flow the pump can't generate those high pressures. This part of why running w/o a t-stat or restrictor usually results in the engine running hotter. Without the restriction the pump can't generate those higher pressures and the hot-spots flash the coolant to steam.
That has been my observation and experience anyway. YMMV........
AND, a great theory partly shot to pieces. The t-stat in the Wagon is stamped 195°
I just started your thread so I haven't read everything yet, but I found this post very thought-provoking. As a mechanical engineer I've always thought the common forum posts warning about making your cooling system too free-flowing so that the coolant doesn't have "time to cool down as it goes through the radiator" were complete nonsense that have become "common knowledge" through repetition, as I never saw anyone actually experience the issue or have any test data to support this claim and the basic heat transfer theory says that a higher flow rate increases cooling in direct contradiction to the claim.
I hadn't considered the significant pressure differentials that must exist within the cooling system, and it makes perfect sense that high pressures within the block would prevent cavitation (localized pockets of steam) on the cylinders' outer surfaces and ensure efficient heat transfer to the coolant so that it can carry that heat to the radiator.
Removing the t-stat would certainly decrease the peak pressure in the system and therefore increase the risk of localized overheating (which can then lead to things like detonation, blown head gaskets, cracked and warped heads or block, and general overheating).
Based on this I'll have to adjust my assessment of those common forum warnings - not complete nonsense, but a misunderstanding of the actual root cause of an observable problem with removing the t-stat.
Thanks again for your post - I feel like I learned something today
. I look forward to catching up on the rest of the thread