Sorry to put this back OFF topic, but I want to correct a couple of points: Lubrication Basics 102
The SAE J300 viscosity classification system defines 2 series:
Those containing a "W" are winter grades (the SAE made it pretty simple in the old days), defined by cold cranking viscosity(ASTM D5293) and low temp pumpability (ASTM D4684) tests. In effect, they relate to the ability to start and supply oil in a cold engine. Depending on the test and the oil viscosity, tests are done from -5 to -40 deg C.
Those without the "W" are summer grades, defined by kinematic viscosity(ASTM D445) at 100 deg C and High Temp/high shear viscosity or HTHS (ASTM D4683 & D4741) @ 150 deg C. In effect, this simulates the actual oil viscosity under operating conditions in the engine.
A multigrade oil (like 10W-40) means it has been tested at both ends of the system. Which is why you can buy 20W-20, and oil that is a 20 grade at both low and high temp.
One other comment, all oils (and basically all fluids, including air) get thinner (lower viscosity) at higher temperatures, and get thicker (higher viscosity) at lower temperatures. As almost all North American mineral (dino) olis are based on Parafinic crudes, they also contain Parafin wax, which can really cause them to thicken up as the temperature drops.
As for what we "feel" as we shift the transmission, this is much more subjective. Thicker oils (higher viscosity) will provide more "cushion" between the gear teeth, usually making things quieter. BUT, higher vis oils tend to run hotter, due to the increased friction.
SAE 40 oils (0W-40, 5W-40, 10W-40, 15W40) tend to be the right comprimise in our engines. But let's finish with a general statment. Using a quality engine oil (API SH or highter), of the correct viscosity (SAE 30, 40 or 50 are all OK) changed regularly, will have everyone at 90% or better. We are only niggling over the last little tweaks that are largely subjective.
Sorry for the thread hijack. Unless you spend a LOT of time under ilde conditions, I wouldn't be overly concerned about the rise in temperature (but I don't have any data on what is actually happening to oil temperatures). The higher temps WILL decrease oil viscosity, but it starts out higher than the ENGINE section needs. Lower oil vis could cause the clutch to get "grabby" and the transmission to become noisier, but should not result in any significant increase in wear. Just avoid low revs/high loads until the engine cools a bit.