I have a BMW I’m supposed to only use synthetic oil in. I want to do an engine oil flush with an additive. Can I use regular oil since I’ll?

News flash, no engine manufacturer has ever, in the history of internal combustion engines on planet Earth, ever been able to win a lawsuit against a motor oil manufacturer, period. So long as the motor oil, ANY MOTOR OIL, meets the API standards (currently API SN) listed in the owners manual. Just don't believe the silly suggestion that you can change the motor oil once in a great while. There's no "super motor oils" that can leap tall buildings and outrun speeding bullets. I'd not go more than 200 operating hours on ANY motor oil. 200 hours at 70 MPH would be 14,000 miles. IF you have a two to three gallon oil pan and you use a full synthetic, then I'd go 200 hours on an oil change. Car manufacturers like engines that wear out, the sooner the better. Flush it with any off the shelf engine flush and you'll be just fine.

Just do a synthetic oil change, no flush.

Why?? where did you the crazy idea to do that? If you wish to add an engine cleaner just put it in before the next oil change....

Do you plan on taking the oil pan off immediately after doing the flush?

If you don't take the oil pan off and clean all of the sludge out that ends up in the pan after flushing it the sludge gets sucked into the oil pump screen and you end up with no oil pressure and seize up the motor.

You don't need to use synthetic oil but I sure as hell would not use any flush product in your motor!!

Dumb idea.

Flushing is a myth and it will not do any good at all. Modern oils hold contaminants in suspension. The filter removes larger particles and the remainder comes out by draining when the oil is hot. Refill with fully synthetic and that's the very best you can do. It's a mistake to use other than fully synthetic as this stuff protects your engine and lessens bad emissions. You can buy fully synthetic at half the price of branded oils at supermarkets or online. It's all to the same specification.

I know of no valid reason to flush, so not knowing why you want to flush I can think of a good reason to use inferior oil. I guess my question is that if enough oil is left when you change the oil that you need to flush why would you want to leave that same amount of inferior oil?

Do not flush. It is NOT required. And you are removing the residual oil on the surface of the engine parts when you flush which is really BAD for the engine. You want the residual oil to stay on the engine to help lubricate the parts during start-up when oil pressure is ZERO.

You don't need to do an engine flush. That's what an oil change is.