Old wives tales never go away.
In the early days of synthetics, some of them had excessive cleaning properties and caused some trouble with older engines that had a lot of sludge buildup. Both from causing leaks, to loosening up so much sludge it clogged the oil passages. This had not been a problem since the 60s.
About switching brands, in the VERY old days the two main types of crudes (Pennsylvania and California) were different enough that they could cause trouble if mixed. So you didn't want to switch oil brands in case you mixed crude base stocks. With modern refining, all the oil is pretty much the same once it comes out of the refinery. This has not been a problem since the 50s.
Of course the oil companies would like to not switch brands, but that is because they want your money.
As to what oil to use in your BMW, if it is under warranty, you should use BMW oil. The reason is, since BMWs come with a maintenance agreement, where they supply things like the oil, if you use other than the factory recommended stuff, they COULD (not that they will, or even that it is likely) void your warranty if any problems occured that might be related to supplied parts (oil). And as I understand the Magnuson- Moss Warranty Act, since they suply the il, they do not have to prove that the other oil caused the problem, just that you used other than what they supply. For other (items not supplied under maintenance agreement), they would have to show that the aftermarket item actually caused the problem.
As to BMW Synthetic not being the same as off the shelf Castrol (or Valvoline, I have heard both as sources depending on the timeframe), this is most likely true.
BMW specifies ACEA A3/B3 spec oil. ACEA is a testing standard like SAE. No off the shelf -30 weight oil meets ACEA A3/B3. They only meet ACEA A1/B1. I have checked every -30 (0W-30, 5W-30, 10W-30) I could find and if they are ACEA tested, they only meet A1/B1
So if BMW oil actually meets their own specs, it is not the same as off the shelf anything. I will check today when they do the annual oil change on the Roadster.
BTW for the Redline fans, Redline is NOT ACEA tested. I have seen posted that when questioned, Redline said they figure their oils would meet ACEA A2/B2. Not quite up to BMW specs. This does not mean I don't like or dislike Redline, just pointing out something you should know.
JJKK said:
I have seen some comments that it is not good to use Mobil 1 synthetic in a new engine , but once the engine is broken in, Mobil 1 is fine to use and actually a good choice.
Does anyone know what the reasoning is here?
Also, can anyone explain the problem that some have mentioned with switching back and forth between brands of oil?