20w-50 is designed for very hot climates with mild winters. It's good for diesel motors, motorcycles, and high performance cars.
For example, my 1991 Volkswagen Jetta with the 1.6 litre diesel motor calls for 15w-40 or 20w-50 oil. Harley-Davidson motorcycles call for 20w-50 oil as well. And back when I was a teenager and had my hot rod (1966 Chevy Bel-Air) I ran Mobil 1 15w-50 oil in it.
I bet that 90% of the people who are running 20w50 would see better wear numbers with a 5w40 or 10w40 though. Only those engines running super huge clearances would see better results with the 50wt oils.
20w-50 is still the biggest seller by far in Australia. I guess its because of our hotter climates. 40wts are beginning to take over, but they wont be the majority any time soon. And I highly doubt we'll ever see 30wts in large quantities on the shelves. Only the latest OEM oils are that thin!!
Even M1 is still only available in 5W-50 in almost every store (eg Kmart) unless you go to a specialist to get the 0W-40/10W-30 (which is double the price too!) Not to mention we dont have SuperSyn.. Aus are wayyy behind..
Here in GA I see plenty of 20W-50 and other heavy weights on store shelves. Last nite at AutoZone I saw 20W-50 from several mfrs and weights up to 60W available (Valvoline). Stores that carry Kendall oil will offer from 30W to 70W.
There are a number of shops that use 20W-50 in their customers cars. I have a friend with a mid 90s BMW 318i with the 1.8L 4 cyl and the indy shop she takes it to always uses Valvoline 20W-50 in her car. These guys swear by it, especially during the hot, humid summers we get here.
So while I think there is still a use for 20W-50 I agree with those who feel other viscosities would be a better choice, depending on oil type.
The reason why so many stores carry 20w50 is simply supply and demand. Just like the 3000 mile oil change interval, many people don't want to let go of their using 20w50 oil either.
Like I've asked many times on here though, somebody please show me proof that 20w50 or 15w50 oil is giving them lower engine wear numbers than 5w30/10w30. I've yet to see a UOA on these thick 50wt oils which show me that they are all that great. We've seen more than enough reports which show extremely low engine wear with 5w30 and 10w30.
Why are some things posted, re-posted and re-posted.....
We've already established this: There is NO difference in the engine "tolerances" between those that recommend 5-20 or 20-50. In fact, we've seen both recommended for the same engine depending on the continent.
Secondly, as far as wear numbers are concerned. I've already said...UOA DO NOT show the whole picture. I've used 5-30 oils in a vehicle recommending 10-40/20-50 and the like. After 60-80k, the amount of sludge due to burn-off and consumption was unacceptable. Will I go back to a 30 weight? Forget it. And neither will places like Australia if you guys think that adding 1qt/3k miles or more is normal...because it's not.
I like 20W50, 15W50, 15W40 oils if the ambient temp. permits their use. I lived in Ga. for a number of years(Ft. Benning,Ft. Stewart and Savahna ). You could not pay me to run a thin oil in a hot climate. P.S. I freely admit that I like the heaviest viscosity oil that temp.'s will allow.
If you look at the Check-Chart publications, 20w50 is still recommended for a lot of vehicles, including some new ones, mostly Japanese. It is recommended for older BMW's and I have it in my:
1988 BMW 325ic
1987 Mitsubishi Fuso
1987 Nissan Condor
1991 Geo Tracker
1995 4 Runner Diesel
1997 Mazda pickup (was consuming 15w40 when I got it from someone who owed me money)
I use 5w30 in my two Fords
and 15w40 in the rest.