Rx350 Puzzle...rx300 Atf Overheating?

[wwest]

The RX300 used a viscous clutch/coupling across the center diff'l along with overdriving the rear driveline in order to have a "full-time" AWD system that required no interaction of the driver. With the introduction of the RX330 the overdrive level of the rear driveline was actually increased although the VC was dropped entirely.

Now I see the new RX350 has the VC again.....

And the F/R final drive ratios are back to those of the RX300.

We have all heard stories of the early, premature, transaxle failures in the RX300 series and I can vouch for the fact that something unusual is causing the ATF to be compromised long before the factory estimated it would need to be serviced.

At 40,000 miles the ATF in my AWD RX300 was smelling burned and looked brownish although the manual indicates no ATF service is required for the life of the transaxle.

You may notice that the PTO, power take-off assembly/case has lots of heat disapating cooling fins on the exterior. The way the VC works is that the viscous fluid is quickly heated whenever there is a disparate rotational rate between the front and rear drivelines and being hermetically sealed it cannot "expand" so the result is compression, thickening, of the viscous fluid.

Obviously this heat must be "wicked" away fairly quickly and rapidly in order for the center diff' to return to its normally "open" state once the wheelspin/slip has abated. Thus the numerous cooling fins on the outside of the PTO case which contains the VC.

But.

What if it was the heat from the VC, transferring through the metal "wall" separating the PTO and the diff'l case that was overheating the ATF beyond its normal operating temperature?

Does the PTO in the RX350 have better heat "disposal"??