BMW Oil Tidbits

5w-30 vs 5w-40

  • One thing to realize about what the OEM oil recommendations is that they do NOT recommend an oil weight/viscosity (5w-40 in this case) that provides the best wear protection and longevity for the engine. OEM’s are fighting every day, every year to meet the increasing mpg requirements put in place by the government. Using thinner/lower viscosity lubricants can get the OEM’s 0.5-1% better gas mileage. If you look at OEM’s viscosity recommendations over the last 30 years you can plainly see that they used to recommend 5w-30, 10w-30 and 5w-40 and now all manufacturers are all moving down to 0w-20.
  •  My advice is to run a 5w-40 (at least) that is high in zinc. BMW's B58 run better and burn less oil on a 5w-40 than a 5w-30 and especially better than the OEM recommendation 0w-20. 
  • BMW recommends a 0w-20, but as soon as you start using the oil, the viscosity begins to degrade/breakdown and by the end of your interval it can have the viscosity of a 0w-10 or lower. This is due to fuel dilution, water dilution and thermal breakdown. By starting with a 5w-40 the viscosity will stay in spec and over 5w-30 levels for the entire duration of its use.  
  •  Many people run Motul 300v 5w-40, Penzoil Euro 5w-40, Liquid Moly 5w-40 and Rotella T6 5w-40 (there are of course other options out there that are great to use also). Most of these oils have high zinc content which is one of the best anti-wear additives for protecting the bearings.  The reason many people run Rotella T6 is that it has equal zinc content to all the above "racing" oils yet it is half the price and is readily available at Walmart, Pepboys, etc. for $20ish.
  •  Lots of people get scared of 5w-40 oil because they think it’s worse for cold weather use, but the “w” in the 5w part stands for winter.  So the 5w-30 and the 5w-40 have the same cold temp viscosity.  The only difference between the 5w-30 and the 5w-40 is that the 5w-40 performs better in hot temps and keeps the viscosity up as the oil degrades through usage. 5w-30 is only rated for use up to 95 degree ambient temps.  5w-40 = 104 deg, 10w-50 = 113 deg and 10w-60 = 122 deg.  I suggest 5w-40 be used at a minimum
  • Base your oil change interval on your driving. If you beat on the car the whole time, change your oil at 2,500-3,000 miles max…..if you daily drive your car and just get on it occasionally; change your oil at 4,000 miles. Beyond that send off a sample to Blackstone and get it checked to know for sure if you can go for a longer interval.
  • The only way you can truly know what’s going on with your oil is to get it tested. It will let you know when something is going wrong.  They send you a vile and you grab a sample of your oil and it will show if your bearings are wearing, or pistons, or block, or cams, or if your oil viscosity is wearing down too fast.