Rob1066 said:
long day of driving. I'm gonna have the shop change the oil as well
and wondered if I should go with something heavier (maybe 15-30 or
10-40) instead of Subaru's recommended 5-30. Car is 1999 Forester with
Hi,
Are you going to be driving thru some pretty good heat all day?
Something like 100 deg F (38 deg C) kinda stuff? Loaded heavy? If so,
you probably won't hurt anything going from a 5W-30 to a 10W-30.
Time was, Subaru and other mfrs didn't recommend the use of 5W-30 for
extended highway driving, but oil, and engines, have changed enough
that's valid advice today pretty much only if your owner's manual warns
against it (it's probably ok'd by '99.) Building on what "Nobody" said,
a healthy engine oughta do just fine on the "standard" recommended
weight.
Considering how quickly you'll be piling on the miles on this trip, you
may want to go the 10W-40 route, IF it's gonna be truly hot AND your
engine's a bit loose (though it shouldn't be at 106k if it's been
properly cared for) and the owners' manual specs it as ok. You won't
hurt anything under those conditions, though it's POSSIBLE a very slight
reduction in fuel economy could occur. Probably not enough to worry
about, though.
My old '90 was one of the "don't use 5W-30 for extended highway use"
models. So I normally ran 10W-30 during the winter. It's routinely 100
deg F and above here during the summer, and I've tried both 10W-40 and
15W-40 in the past to compare to 10W-30 performance. Interestingly, my
fuel economy did go DOWN (tiny bit) w/ the 10w-40 but UP (tiny bit
again) w/ the 15W-40! So it's truly a YMMV thing!
Some might recommend switching to a synthetic in the 5W-30 wt (if you've
been using dino oil.) If you had some time to put some miles on BEFORE
the trip to see if it leaked or anything else negative happened, I might
join them. Otherwise dino oil's just fine.
Have a fun, and safe, trip!
Rick
