I would like to clarify some points that I missed:
The coolant temperature was almost 100C while I was stuck uphill at Death Valley for 3 hours to go less than 5 miles with air conditioning at full blast, but as soon as I passed that construction area and resumed normal speed of 85+ mph, the coolant temperature dropped back to below 85C which was normal temperature with Mobil 1 0W40.
I mentioned that Pennzoil Platinum 5w20 got darker much sooner than Mobil 1 0W40, I think it may be cleaning the deposits of using Mobil 1 0W40 for up to 13.5k miles between oil changes. The car has oil life monitor which MB calls FSS, that tells us to change oil from as little as 10k and as much as 15k. Saw that PP got darker sooner actually made me feel good that it did the cleaning job that I did not expect it to do.
The car did not consume any measurable oil with either Mobil 1 0W40, Pennzoil Platinum 5w20, Delo 15W40 or Mobil 1 0W20+10W30 mixed. One of the reasons that I tried thinner oil with this car was it did not consume oil with Mobil 1 0W40 until 90k miles, I expected that with 2 grades thinner it may consume some oil but none what so ever and it was a real surprise to me.
As someone said, thicker oil may quiet down engine noise and thinner should make engine noise louder. But I observed opposite direction: loud with Mobil 1 0W40, quiet with Pennzoil Platinum 5w20, loud with Delo 15W40 then quiet again with Mobil 1 0W20+10W30 mixed, specially at idle the car is so quiet I could not hear any engine noise at all with Pennzoil Platinum 5w20, my observation about quietness with thinner oil(s) was confirmed by wifey. If I can find Pennzoil Platinum 0w20 at local store(s) I will try it in this car.
This car is mostly driven in city streets, 90-95% of the trips are less than 7 miles, 3-4% are more than 10 miles but less than 15 miles, less than 2% are more than 15 miles. Because of short trips, I think thinner oil would help engine get to operating temperature faster.
These observations may contradict normal thinking, if any point I posted that you guys think is not valid or had been proven wrong in the past, please post then we can discuss. One thing I would like to say is, don't flame me for using thinner oil than manufacture recommendation, it is my car and if anything went wrong with using thinner oil I would be the guy who pays for the experience. I wanted to verify what Dr AEHass put on his white paper, and so far he is correct.