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      03-30-2011, 06:58 PM   #46
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Quote:
Originally Posted by mrgold View Post
After reading this thread I am compelled to step in as wrong information is bad for our whole BMW community. The main reason I am chiming in is to correct the mistaken claim that by using the heavier weight TWS 10w-60 oil in the motor that somehow oil flow will not be sufficient for sustained high RPM situations. That simply is not true. The S63 engine is NOT going to mysteriously melt down, prematurely wear out or blow up due to insufficient oil flow at the top end of the rev range just because of using the TWS 10w-60 motor oil. PERIOD! Why?

1. Believe it or not BMW (especially M division) is not that stupid to build an engine which can be that easily damaged just because a customer is using the thicker performance motor oil (especially their own BMW approved high performance motor oil).

2. The viscosity thickness difference at regular operating temperatures 100 C (212 F) for the 10w-60 and the 5w-30 is much closer than what most people think.

Viscosity chart http://www.bobistheoilguy.com/visc.html

Viscosity of 10w-60 @ 100 C (212 F) = 21.90 – 26.09 range
Viscosity of 5w-30 @ 100 C (212 F) = 9.30 – 12.49 range

The true viscosity difference between the two motor oils at operating temperatures will be about 12 and not 30. Therefore at regular operating temperatures the 5w-30 is actually at about 10 viscosity and 10w-60 is at about 22 viscosity which is definitely “thin” enough for oil flow at high RPM.

3. Oil pressure rises as engine RPM rises. There is plenty of oil pressure @ 7000 RPM to assure sufficient oil flow for the heavier weight oil. Especially at normal operating temperature when the 10w-60 is actually only at 22 viscosity.

On a side note, I just called 3 different BMW dealers in the Los Angeles county area and 1 in San Francisco and all 4 BMW techs said the TWS 10w-60 is the correct oil (preferred) for the engine according to their service computers. One tech did state that the standard 5w-30 can be used as an alternative when TWS 10w-60 is not available but not recommended if the customer will be doing any high performance driving. That being said, there might be different recommendations for different areas with colder climates but I have not heard or seen anything about it. For me I would choose the TWS 10w-60 oil simply because it is the best oil available approved by BMW M.
Your numbers is quite correct for the viscosity of the 2 oils at operating temperature. However, you forgot to notice that a difference of 12 in the viscosity rating already means a 100+% increase, that's doubled.

Oil pressure is a product of flow and viscosity, the ratio is almost 1:1 as the oil line size is constant. Since BMW regulate oil pressure in engines, once they reached the limiter they stay there, as there is a pop-off valve to relieve excess pressure. In simple terms if you double the viscosity the flow is halved at any given pressure. Oil served 2 functions in an engine, oil pressure is for lubrication as the pressure keeps the metal parts separated, oil flow is for cooling, it carries away heat.

You can see now an engine spec-ed for 30 viscosity oil will have double the flow of a 60 viscosity oil at operating temperature with a capped oil pressure point.

Unlike earlier specialized purpose build M engines, BMW didn't cast a new block for S63 engines, it still uses the N63 block, and same architecture of the regular N63 like reversed intake exhaust heads. It's just a tuned version of the N63. Even if it has extra oil passages for the thicker oil to increase flow,which I doubt, the lighter 30 oil will still have double the cooling capacity while providing the same oil pressure for lubrication.

TWS 10w-60 is not the 'BEST' oil approved by BMW, TWS is only SJ rated, 2 steps behind current standard, even the RS 10w-60 is only SL rated, one step behind current. BMW's own factory 5w-30 is SM rated, the best available as API has a much higher tolerance and standard for SM than SJ or SL rating. To the best of my knowledge, the TWS and the Castrol didn't meet the higher SM standard.

60 in the oil doesn't mean it's better than a 30, it just means thicker, but a API SM rated oil is definitely better than a SJ or SL rated one.
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