I'm definitely not arguing that water/air delta's are not useful. I use them myself. I was just pointing out that the statement you made about water in/out delta's not changing when you have a load on the system...is definitely not going to be true for all systems.

I think both measurements can be useful. If you have a very effective cooling system....the water in/out delta will be the first indicator that changes once a load is being applied to the system. You showed an example in the graph (love the graphs by the way...i have several like it) that showed the coolant temp (and therefore the water/air delta) taking off almost immediately under load. But you also said that this was with no fans spinning. Because I can run my fans at 500 rpm and not hear them at all....they will probably always be spinning slowly. And when I do this...my coolant temp does not shoot through the roof when the system is under load. I have a lot of radiators. Seven of them. And my coolant temp NEVER rises quickly like you are showing in your graph. It's a slow rise....depending on how long the system load is applied. All of my radiators and slow spinning fans are just too effective at removing heat from the coolant for the coolant temp to rise quickly. So....the thing that changes the most temp wise in my system when it is under load....is the water in/out delta. The water in temp immediately gets hotter as the blocks pull heat into the coolant....and the water out temp doesn't change near as much as the radiators do a good job of pulling heat out of the coolant before it finishes the radiator loop.

But I can also see that if someone has insufficient radiator space or inadequate fans...that the water in/out delta would not change much under load. Also, if you don't have all of your radiators together in the loop......if you have blocks in between radiators....then you won't have the kind of changes in the water in/out delta that I have.

Neither of these indicators (water in/out delta nor water/air delta) need an additional controller or different settings depending on the season. Both are attempts at measuring whether a system load has heated up the coolant.

Great discussion and data sharing guys!

No no ... those temps seen on that screenshot are not representative of normal use. Some are very high because no fans were running and stagnant hot air built up.

Both radiators intake air into the case. The front rad air in temp is one of the ambient sensors and the top front and rear are both air intake sensors too ... they have just been overheated in the screenshot because without fans the hot air from the rad rises into them.
Don't worry, I'm always bothering people about their setups that recycle hot air from one rad to another.

BP water is after the GPU and before the front rad, water one is after the front rad and pump.

Water 1 and 2 delta varies because it includes a top rad and a waterblock.

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Yeah I agree there are many ways to control different systems and discussion is great

I suppose I just see too many ways for a rad delta controller to go wrong or behave unexpectedly in most systems compared to an air/water delta controller.
Fan speeds themselves have a much greater impact on rad delta than water temps can so it seems funny to control fans in a water cooling system based on that ... it can be a bit of a feedback loop