why do shops use 10W40?

[celenium]

You all recommended 5w30
here but no matter what shop
I go to, they all use 10W40.
Why is it?
Does it matter?

[mickey513]

Yes it does matter, you will notice a decrease in gas mileage. The reason why a lot of shop use 10w-30 and 10w-40 is because a lot of the older cars use these type of oil. Many shop do not get enough new cars in for oil changes, so many do not stack 5w-30. Even my local Toyota dealer stack only 10w-30.

[kuruptgt]

when i get my oil changed i usually buy the oil myself costs a little more but its better i use synthetic and then i watch the bastards to make sure they put it in. one time i cought em puttin reg oil in and i was like wtf and then they had to drain it out again and put my oil in.

[BoyRacer]

i use synthetic too.....first mobil, then 2-3 cycles of amsoil, and the last 2 were castrol synthetic.

[2000 XYR]

My truck uses 5w20. Seems like it would be really runny. I've always been a believer in "the thicker the better" and I used 10w40 in most of my cars back in high school and college. Then I started using 5w30 in winter and 10w30 in summer for the Celica when I bought it. I've only had 2 oil changes in my truck and I know they used 5w20 the second time. I'm putting 10w40 in my Prelude and Bronco though -- both are older.