The lube & oil change place put the wrong viscosity oil in. Do I need to change it immediately?

Dear Car Talk

Dear Car Talk | Dec 01, 1999

Dear Tom and Ray:

I reverently brought my 1993 Mazda Miata to one of those quick-change lube places. Though they changed my oil in a jiffy, when I got home I noticed that the little
window sticker said 20w-50 instead of the usual 10w-30. Should I go back and have them drain and refill it with the usual, or is the thicker stuff OK to keep in there for
the next few thousand miles? I live in Los Angeles. -- Dave

TOM: You're probably OK with 20w-50 in Los Angeles. If you lived in Anchorage, I'd tell you to march right back. On the other hand, if you lived in Anchorage, you
probably wouldn't be driving a Miata!

RAY: 20W-50 is a thicker viscosity oil. It's designed for hotter climates, severe duty -- or sometimes as a last resort for junk boxes that are burning the thinner oil at an
unacceptable rate.

TOM: But in my experience, the only effect it will have is on your fuel economy. Since the oil is thicker, it takes a little more energy to move the engine parts around,
and your mileage may drop by a fraction.

RAY: But mechanically, it shouldn't cause you any problem. In the future, you might want to let them know at the outset that you want 10w-30 (actually, most newer
cars call for 5w-30, so check your owner's manual). And let them unload the 60,000 gallons of 20w-50 they got on sale on somebody else.

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