These questions are for anyone who KNOWS the answers.

1) Ok, so why the 0 weight oil anyway? I mean, my 85 truck called for 10W30 and my 1993 truck called for 5W30 and now the car calls for 0W40... why this trend? Why are manufacturers calling for thinner and thinner oils?

2) Why the recommendation for synthetic oils?


An additional note: In the past two trucks I've owned, which I mentioned above, I ran the recommended oils until about 15,000 miles. At that point, I switched to 15W40. At around 85,000 to 100,000 miles, I changed to 20W50. I believe it best to use a heavier oil in a high mileage motor, and I also believe that heavy oils in general are best. When I told a guy years ago that I was running 20W50 in my 93 truck I mentioned above - he told me I'd ruin the engine because the oil cap says "5W30 only" on it.

Well, it is owned by a friend. It is still running and rolled over 383,000 miles on my birthday this year. Original engine, of course.

It bugs me to put 0 weight oil in an engine, but I am doing it. Someone educate me. Please.