FWIW a GM engr that used to frequent this forum advised to change mineral oil at 50% and synthetic at 0%. Also said 5W30 is the best to use.

 

Very informative post. Hard to imagine it can work with synthetic or regular oil.

 

Well all it's calculations are designed around the spec oil for the car at the time of production, it actually doesn't know what type of oil you are using. So if you are using something better, i.e. synthetic (assuming it wasn't factory fill), then it's just extra protection and there is nothing wrong with that.

FWIW, I've been using Mobil1 since the mid 90's and have been changing it between 6000 and 7500 miles (on cars w/o an OLM) using a high quality oil filter. I've suffered no issues as a result (214k on one of them). So now with the OLM telling me I can go ~9000 or beyond doesn't bother me in the least.

 

I've heard that rumor before but I'm highly skeptical since the majority of cars don't come with synthetic from the factory and they tell you to follow the OLM, which is designed to calculate the oil life based on the factory fill and it's a very conservative estimate at that.

 

I wouldn't consider it a rumor since it was first hand info from a GM engr.

 

Not first hand to me.

The only first hand stuff from an engineer I've read is from my post above and thread I linked to. I'm also sure there are lots of engineers at GM, not all of them work in the fuels & lubes group.