Dr T wrote: Why doesn't redline or amsoil make this grade available?
Probably because there isn't enough market for it.
I know that AMSOIL made up a small amount a number of years back as a test, but decided that the demand didn't exist.
40 Weight is plenty high a viscosity for modern engines. Attempting to formulate a 5W50 requires a lot of VII's, and no matter how "shear stable" they are supposed to be, they will still shear. I just don't think its necessary to have a 5W50. I think 5W40 is about as wide a viscoity range as is necessary for today's engines.
There are a few modern applciations for higher wieghts. The BMW M3, for instance, requires 10W-60 Castrol Syntec. This stuff is quite expensive at the BMW dealer.
What is the specific application for the 5W-50?
Is the Bavarian Motor Works 10W60 specification a suggestion, a bonofide requirement based on specific engine operating conditions, or is it based upon some marketing agreement between Castrol and BMW?
I think your question regarding 5W50 is very valid. What automaker specifies a 5W50 and for what reason?
The extreme temp propertie of 5w-50 grades tend to be fairly average. They don't perform as well in cold weather as a 0w-30/5w-30 and they don' t perform as well in hot weather as a 15w-50 or 20w-50.
For your BMW I'd switch back and forth between a 0w-40/5w-40 and a 20w-50 in warm to hot weather. That will give you more optimized results throughout the year. I know you have this aversion to 5w-30 oils so I'm not even gonna suggest that grade.
The BMW M3, for instance, requires 10W-60 Castrol Syntec.
Of minor interest, in mid 2001, BMW ordered an oil change on the M3 - the 5w30 oil which had been shipping on all cars was ordered changed to a new special BMW-only 10w60.
New cars came with the new oil, and 5w30 cars were asked to come in for a free change to 10w60. This seemed to be some kind of reaction to concerns over long term high rpm running ability, and the oil having enough high temperature capacity to hold together on such autobahn blasts.
BMW engine oil recommendations update
BMW has updated the information on engine oils for its M-vehicles from the information published in the May 2001 issue of Service Tech in a later service bulletin. Three different engines have been used in recent M-vehicles: the S62 4941 cc V-8 engine used in the M5 E39 (current 5-series) and Z8 roadster, the S52
3152 cc I-6 engine used in the M3 E36 (previous 3-series) and early M roadster and M coupe, and the S54 3246 cc I-6 engine in the M3 E46 (current 3-series) and current M roadster and M coupe.
S62 V-8 engine oil
Internal design changes were made to the S62 engine early in 2000, calling for different engine oils to be used in M5s produced up to March, 2000, and another oil for those produced from March, 2000, on. All Z8 roadsters have the later S62 engine. The only approved oil for M5s before the 03/00 break date is Castrol Formula RS SAE 10W60 synthetic oil. This oil has been specially developed and formulated for BMW Motorsport. Do not use any other engine oil in this S62 engine.
The Castrol oil also should be used when topping up between oil changes. If it is not available for topping up, use small amounts of synthetic engine oil meeting the API specification SH. BMW advises that oil consumption will increase slightly when the Castrol SAE 10W-60 synthetic oil is diluted with other low-viscosity synthetic oils. Castrol Formula RS SAE 10W60 synthetic oil can be ordered in 1-L bottles cans under BMW part number 07-510-009-420.
A lower viscosity synthetic oil meeting API service classification SH or higher should be used only when topping up oil level when Castrol Formula RS SAE 10W60 is not available. For M5s built from 03/00 on and all Z8s, the recommended oil is BMW
High-Performance Synthetic Oil SAE 5W-30, available in one-quart bottles under part number 07-51-0-017-866.
S52 I-6 engine oil
The recommended engine oils for the S52 3152 cc I-6 engine are BMW High-Performance Mineral Base Oil SAE 15W-40, part number 07-51-0-017-868 or part number 07-51-0-017-866, as mentioned above for the later S62 V-8 engine.
S54 I-6 engine oil
The recommended engine oil for the S54 3246 cc I-6 engine is BMW High-Performance Synthetic Oil SAE 5W-30, part number 07-51-0-017-866, as mentioned above for the later S62 V-8 engine.
Engine oil level check procedures
To further complicate maintenance, the engine oil level checking procedure is different on the S62 V-8 compared to the S52 and S54 I-6s. All vehicles should be on level ground when checking the oil level. Since oil consumption tends to greater on M-vehicle engines, BMW suggests checking oil level at every refueling stop. The distance between the full and low marks on the dipstick on these engines is 1.1 qt (1 L).
S62 engine oil level check
With the S62 engine at normal operating temperature, let the engine idle for 15 seconds, then turn it off. Wait at least 1 min for the oil to drain down into the sump before checking the level with the dipstick.
S52 and S54 engine oil level check
With the S52 or S54 engine at normal operating temperature, and turned off, wait about 5 min for the oil to drain down into the sump before checking the level with the dipstick. In summary, most M-vehicle engines now use the same engine oil: BMW High-Performance Synthetic Oil SAE 5W-30. The V-8 and I-6 M-vehicle engines use different oil level checking procedures.
[ April 08, 2003, 11:13 AM: Message edited by: tenderloin ]