Has anyone put 10/40 oil into their machines ----BMW say they take 5/40 and Shell say its ok to use 10/40 as its better at high temperatures and its cheaper.
Paul Jones
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5,374 Posts
First, 10W-40 is not better than 5W-40 at high temperatures. The "W" value is the viscosity at cold temperature. At normal engine operating temperature (and above), 5W-40 has the same viscosity as 10W-40 (they are both a 40-weight oil).
Lots of engines call for various oil weights based on temperature. However, the manual for the R1250 says "5W-40" without any mention of temperature. Based on that, I would say you should use 5W-40. I think there are 3 major factors here:
1. Thinner oil lubricates better at cold engine startup.
2. The alternator in that engine is cooled by the motor oil, and thicker oil might not do as good a job.
3. If your bike is still under warranty, if you need to make a warranty claim and it becomes known that you used a non-spec motor oil, they may not honor the warranty.
Lots of engines call for various oil weights based on temperature. However, the manual for the R1250 says "5W-40" without any mention of temperature. Based on that, I would say you should use 5W-40. I think there are 3 major factors here:
1. Thinner oil lubricates better at cold engine startup.
2. The alternator in that engine is cooled by the motor oil, and thicker oil might not do as good a job.
3. If your bike is still under warranty, if you need to make a warranty claim and it becomes known that you used a non-spec motor oil, they may not honor the warranty.
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5,374 Posts
And you have just encountered one of the chemical engineering challenges involved with creating motor oils: breakdown of viscosity modifiers. A 5W-40 oil requires more or different viscosity modifiers than a 10W-40 oil to achieve that 40-weight at operating temperature (100 °C). As the oil ages with use, the 5W-40 oil might actually become a 35-weight oil at 100 °C, whereas the 10W-40 oil is more likely to still be a 40-weight.
By far, the largest amount of engine wear happens at cold start and during warm-up. BMW specifies 5W for a reason. Change your oil at recommended intervals and use the recommended oil.
Or don't.
If you would like some light reading on the subject, try Motor Oil 101 - Chapter One - Operating Temperatures and Viscosity - Bob is the Oil Guy
By far, the largest amount of engine wear happens at cold start and during warm-up. BMW specifies 5W for a reason. Change your oil at recommended intervals and use the recommended oil.
Or don't.
If you would like some light reading on the subject, try Motor Oil 101 - Chapter One - Operating Temperatures and Viscosity - Bob is the Oil Guy
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