Hum, isn't the first number 5w, the cold crankability of the oil? And, doesn't have anything to do with 50w thinning out to 5w?
Thats what I was always led to believe as well. 5w til it warms up, then its 50w. In my manual it recomends to use 10w40 in weather below 40F. Thats on the 99 ultra.
***************************************************
OKAY, this is what I meant...
You have a 5w, yes that is a 5 weight oil.... Never any heavier.... the 50 relationship tells you ONLY How Long the 5w Will stay-remain a 5w as compared to the 50 weight oil as it is Heated....
So IF you take a straight 50w and HEAT it up until it Becomes a 5 weight, that is the amount of Heat protection you have Using the 5w oil....
This Shows that 50w, Heated to the MAX temp. it takes to make the 50w INTO a 5w oil.
This Is used JUST to compare the 50 weight (how long the 5w will REMAIN a 5w when Heated) BUT Never will the 5w become a 50w oil JUST will remain the 5w it is. 5w50
If you HEAT a 50w oil Hot enough to become a 4w oil...... That is the same amount of Heat it will take to make the 5w into a 4w ALSO.= comparison only here..
Now COLD works the other way
IF a 5w get cold enough it WILL become a 50w and pour like a 50 weight.... at that temp, but IF you compare it to a 50 weight at the same COLD temperature,
the 50w will not pour like the 5w, even when it is the same COLD temp..
that is MY take on this..
They put molecules into the oil to KEEP IT at a 5w.....
NO matter what the last number is, 50, 60, 80, The oil WILL be a 5w
When it gets warm it is a 5w and when it gets HOT, it is a 5w... UNTIL it gets TOO HOT.... Then it Will start to FALL Under the 5w number.
PHeeewww
signed....BUBBIE