mt_goat

LOL, I had the pen in the pic for size comparison.

Nelsonmd

To be fair, it really is just B&M that's correct. I learned it from them...

Yeah, I am not surprised that your temps have been fine. I am a BSME too, so this was kind of a fun discussion. I would love to see some visuals of a cooler filling. I would also like to see the flow analysis across temps that B&M has apparently done to see the flow ratio's in the bypass vs the rest of the cooler at low and high temps. Without a temp activated switch like in the inline bypass switches, it becomes a more subtle effect.

mt_goat

Yeah, I'll keep my eye open for something clear with lots of small tubes, but so far I've not thought of anything except making a manifold with lots of thin plastic tubing going out the side and into other manifold, but I"ll need some R&D funding to get that motivated.

One possible variable I've thought of is whether or not the cooler drains into the pan during shutdown and factors with that may be the cooler being higher or lower than the tranny.

RSR

I suppose that makes sense when you consider that gravity's likely more powerful than thermal flow...

Regardless of where tranny cooler is mounted, bottom will ensure that full cooler fills with fluid before exiting as there will always be fluid/system pressure to push the fluid through, it doesn't rely on thermal convection/flow (i.e., heat rising, cold sinking, etc) to move fluid through..

RSR

Even if it drains, the amount of fluid in the pan is what matters so no real net negative here. Once the system is on and running, the fluid flow should refill the cooler before any system damage could be done from excess fill in the pan (primarily through bubbling/frothing, I'd think -- not just exposure to fluid, unless it has a fair bit of water mixed in -- why it's important for tranny fluid to be at operating temp to steam off and not just "as cool as possible").

It also makes sense as to why B&M recommends in bottom and out top when mounted sideways. Gravity should keep fluid in place and combat any suction, except perhaps the little bit in the input and/or output hoses that would flow back to the pan via gravity. Not sure how the tranny pump works but it likely has some back flow anti-drainback prevention in it too, so it's likely just the output/return hose that would be a potential issue, but not the input. And if routing through standard radiator cooler on the way back too, it would also help to mitigate any excess backflow too I'd think.