Originally Posted by MolaKule
In transmission parlance we use two temperature definitions and one is "flash" temperature and the other is "Bulk" oil temperature in the sump.
A flash temperature is one that occurs for a very short time at clutch surfaces and can hit 500F, but this temperature only lasts for milliseconds because of continual cooling.
The bulk oil temp in the sump is essentially the average temperature of the "mix" of fluids coming in from the clutch packs, bearings, Torque Converter, and the heat exchanger (cooler).
When the ATF becomes degraded from being in the sump too long, or due to extreme heat cycling (insufficient temperature control), the fluid oxidizes, the dynamic coefficients of friction change, and the fluid may start leaving varnish deposits on the clutch faces. Hence, my recommendation for ATF OCI's of ~ 30-35k.
Now remember, cooling of the clutch plates and discs is accomplished only when oil flows into and out of the clutch material and faces. The clutch disks are faced with a porous material of a cellulose composite. That porous material allows oil to flow into it during disengagement, and squeezes some oil out during engagement.
Once varnish deposits are allowed to form a "glaze," no cooling oil can flow into or out of the porous material and it and the oil degrades even faster because of the higher (flash) temperature spikes.
Quote
Oil flow is supplied to the clearance between the clutch discs and clutch plates through radial pathways on the hub for cooling and lubrication purposes.
During a clutch engagement, a piston compresses the plates. The oil between the plates is squeezed out of the interface and permeates into and or out of the pores in the friction material. Engagement is completed when no speed differential exists between clutch discs and clutch plates.
Internal Heat Generation in ATs
Entertaining presentation, Mola-so you're basically saying there's no such thing as "too big" when it comes to transmission coolers & sump pans, and even in arctic temps-cooler ATF is ALWAYS better?