No. I run 10w-30 in the winter and 10w-40 in the summer in my truck. My truck burns a bit of oil due to very high mileage, so like in the summer time and it's not time to change it yet, its filled with 10w-40. When winter times comes and it's not time to change it yet, and it gets a bit low, i'll just fill it up with 10w-30. Same for summer. If its summer and filled with 10w-30 that's left over in the motor from winter time and it gets a bit low on oil, and it's not time to change it, i'll just start filling it back up with 10w-40.

On a side note, i know a family member who bought a new chevy colorado. It says clearly in the manual NOT to use 10w-40 or higher. It says to only use 5w-30 or 10w-30 if it's over 30 or so degrees. He keeps it filled up with 10w-40 year round, even when he bought it new with just around 100 miles and it just rolled over to 150,000 last month and he's had no engine trouble. I've also heard that their is a difference between manuals for the us and elsewhere made. for example, I've heard, but never verified it, that if you by a vehicle for the us market, it states like 5w-30, yet if you buy the same vehicle for the european market, it will state like 10w-40, and i've heard some cars on the german market state around 15w-40.

Nope, but your car nor the mixed oil may achieve their designed benefits from the foreign mix.

Not really, change the oil when you have a chance.

no, not a problem. 10-40 is just a little thicker oil.

Thank you very much!

no problem