Percolation? Heat soak? Don't drive during summer??

1990's? My '93 BMW 525i (M50 engine) actually calls for 20W-50 in any temp above 14F. When I got it the valve lifters were ticking and a quickie lube place had put 10W-30 in it. I changed to 20W-50 and the lifters immediately quieted.
But that's the only engine I ever have owned that specified that heavy an oil.