Originally Posted by sloowpoke
The oil chart for my '03 K1200GT indicates something that doesn't make any sense to me.
The chart specifies that 15W40 is only good up to 20°, while 20W40 is good up to 30°, and 15W50 is only good to 30°, while 20W50 is good to 40°.
One of the earlier owners of this bike installed a thermometer/probe in place of the oil filler plug, so I can easily see that regardless of whether the air temperature is 0° or 30°, the temperature in the crankcase is 65° when the bike is warmed up. Additionally, the water temperature gauge reads near the center mark, regardless whether I've been on the road ten minutes or ten hours.
Since this water cooled engine doesn't change temperatures on the cylinder walls or valve train, due to ambient air temperature differences, why are the oil chart high temperature limits based on ambient air temperature? This bike doesn't depend on cooling fins on the head and cylinders, so why does BMW still use a chart that appears to be designed around that requirement?
I'm not sure about your figures or arguments. First I'm wondering if those temperatures are actually minus degrees C. Mistakes get made in typesetting. Have you confirmed them from another source?
Then you talk about the bike's oil temperature. When discussing oil/viscosity and temperature, whilst the running temperature is important at the high end, it's the cold start ambient temperature that is most important and that will be set by the lowest ambient likely to be reached when you start and run the bike - hence the 'W' or winter viscosity figure in the oil viscosity range. Look at this link and the cranking rpm table which is scary.
Another curious thing is the K bike's should be fitted with an 85 deg C thermostat measured at sea level (not 15 psi max the pressure cap can go to) which is fully open most of the time and if the fan comes on at 2/3rds gauge I'd expect the water jacket to be hitting the 90-100 deg C. Is your thermostat there and working or stuck open? Your bike seems unusually cool for Summer climate mixed riding, has lost a cylinder or you are riding it too fast to keep it cool!
I'm interested in the brand of oil temperature gauge because it seemed to me there was a big obstruction behind the filler cap, so I'm curious as to how they get their probe deep into the oil sump. And of course there's another issue, I would expect oil temperatures for this bike to reach over the 100 deg C mark when stalled in traffic and the fans coming on at 2/3 to before redline on the gauge. The oil cooler makes no difference when stalled in traffic either.
So, do you ever get the fans on since you say your bike is always just below mid gauge? The only time I noticed my temperatures unusually low was when I was experimenting with the timing. Gas consumption improved too, but when the static advance was out of spec. the bike wasn't such a good performer.
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