Quote:
Originally Posted by aerobod
In the Z4M the variable redline indicator on the tach doesn't reach the maximum until the oil temperature reaches 75C (167F), it's first major mark is at 50C, so BMW expects the oil to be at least at 75C before using the full rev range. For the Z4M the manual states that normal oil operating temperature is between 80C and 120C, with 100C being the centre position. All current oil specs quote the viscocity at 100C, so for example, a 0w40 oil is thicker than 40 weight below 100C and flows less easily, with a higher likelihood that the oil pump won't be able to pump a high enough volume of cold oil to keep the engine well lubricated at high revs.
I don't use the maximum rev range until the oil is at normal temperature, i.e. 80C, or beyond 120C (which I haven't reached on the track yet, it maxes out at about 115C under very hard use). It is interesting that BMW considers that oil temperature is more important in the ///M cars than water temperature.
With the 135i, I'll use a similar philosophy, when we receive the car in a couple of months.
For any engine, running it hard with cold oil will cause more stress on the components, it just depends on how much risk of wear you are willing to tolerate.
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Yes, it's been a more common useage in the the M engines, but they also rev a lot higher.
Still, using the temps you quoted, it makes sense that the "go for it" oil temp is around the same temp as the thermostat would open.
In the M cars, have you noticed at what temp the coolant gauge is at when the oil temp gauge is showing 167F?
a 0w40 oil is thicker than 40 weight below 100C and flows less easily, with a higher likelihood that the oil pump won't be able to pump a high enough volume of cold oil to keep the engine well lubricated at high revs.
That's not right. "Viscosity" is the resistance to flow. So a 30 weight oil will be less viscous than a 40 weight when hot. Higher weight oil is, or should be, MORE viscous and thins less when temps get really hot.
A 0W40 is a "Winter" rated oil, meaning in sub freezing temps the oil retains it's ability to flow, or low viscosity. The "40" rating means that at higher temps it's just like a straight 40 weight oil, greater viscosity.
Amazing stuff this. Of course, go too hot and the oil starts to lose it's viscosity.
At cold temps, straight 40 weight would be too viscous to flow properly, and the pump would have a heck of a time getting straight 40 to flow in sub freezing temps, and the oil will be too thick to properly lubricate rings, bearings, etc...
Here's a good read on viscosity, and not the part/s of the PDF where there is a relationship between thermostat, proper engine operating temp, and oil temp.
http://www.zddplus.com/TechBrief13%2...0Viscosity.pdf