Quote Originally Posted by green91
Alot of times though an oil company will get in cahoots with a auto mfg and work out a deal to specify for synthetic. Mobil and BMW have done this. Its not like if you put fossil oil into a BMW it will start knocking.
Mobil and BMW? BMW rec's Castrol on most of their caps for synthetic, but developed their own specifications for their full-synthetic requirements in Germany with ELF. ELF is probably the best Synthetic you STILL can't seem to buy in America, and one of the best oils available on the market. Regardless, no oil in a car is going to make it start knocking, not the kind of oil in it. The problem with putting conventional oil into a BMW is that the seals and filter are actually designed specifically for the minute differences in how synethic acts in certain conditions, combined with the fact that the BMW's need extremely high levels of protection for their 11.5:1 and 12:1 comp ratio engines.

To that end, if you ever put conventional in a gas-powered turbocharged car, you are BEGGING for trouble. Synthetic oil doesn't coke up like conventional oil does, which is a neccessary property when you've got an oil cooled turbo.