[GARYD]

The manual says to use 5-30. I have some quarts of 10-30 and 10-40. Will there be a problem using that viscosity during the summer or fall?
My other cars said I could use 5-30 at low temps and 10-30 or 10-40 in hotter temps.
I don't see a problem, but with GM you never know.

 

[RIT333]

Personally, I would mix in a quart or 2 in the summer time only.

 

[scottyyyc]

Viscosity shouldn't matter much in the summer, only winter. You'll be fine.

 

[rcturner]

Don't use the 10-40 in any newer engine. There is a reason they don't want you to put it in a modern engine. It forms sludge inside of the engine. Also, it doesn't flow properly with the tight clearances. It can also cause your warranty to be voided.

 

[GARYD]

But my Hyundai's manual says 5-30 is recommended, but 10-30 or 10-40 are OK if the weather is above o*. My Jeep manual says below 0* use 5-30, 0* and above 10-40 is recommanded. Are different engines that different when it comes to oil viscosity?

 

[Steve A]

Supposedly, the gas mileage will be improved by using the lightest viscosity oil sanctioned by the mfr.

Personally, I use Shell Rotella T (full synth) 5W/40 in my Vette and also in the Hayabusa and it seems to work quite well. Even seems to be fine in the B&S on the lawnmower.