| The reason that 748’s don’t have an oil cooler is that they normally don’t need one because they don’t run as hot as the 9XX bikes. The operating temperature of the bike is still controlled by the radiator and the fan operating temperature setpoints. The function of the oil cooler is to cool the oil - to keep the oil temperature, and consequently the oil pressure, within a designated range for expected riding conditions. However, when you take your road bike to the track, or engage in some spirited riding on a hot day, you can easily push the oil temperatures too high on any bike.
Your oil viscosity selection chart in your owners manual tells you to change to a thinner oil if the expected outside temperatures are lower. Adding an oil cooler essentially shifts this chart, so that now you’ll need a thinner oil for the same riding conditions. Under severe conditions found at the track, an oil cooler allows you to keep the maximum temperatures down, but under street conditions the oil temperatures will drop below the values that the chart serves to promote.
As you can see from the chart, a single modern motor oil with viscosity enhancers can be used over a wide range of ambient temperatures and still maintain adequate oil pressure. So it’s not a sensitive parameter.
During an engine’s development time on a dyno, the oil temperature is monitored to avoid temperatures above 260ºF and below 200ºF to avoid oil breakdown at the high end and excessive pumping losses (and higher pressures) at the low end. These dyno runs are simulations of street riding conditions, but not representative of more severe heat loads during actual track conditions.
So, if you modify your oil cooling system you should monitor your oil pressure and adjust your oil viscosity to assure adequate - but not excessive - oil pressure under all riding conditions. See your service manual for the correct cold idle, hot idle, and running operating pressures.
Under track conditions you should be using a 50-weight viscosity oil to maintain an adequate oil pressure and use a full synthetic oil to give yourself a safety net. A regular oil can begin to lose its film strength at temperatures only slightly above 220°F (105°C), but many synthetic oils can be safely used at temperatures as high as 300°F (150°C) before lubrication-related failures occur.
Specifically, if your oil light begins to flicker at idle because of excessive oil temperatures, then you should consider adding an oil cooler. If you already have an oil cooler, you should carefully straighten any oil cooler radiator fins that were bent from road debris in order to get the maximum cooling from the unit. After you straighten them, attach some protective screening to the backside of the v-piece to prevent future damage.
Some studies have shown that test engines produce optimum horsepower in dyno-simulated racing situations when the oil was between 200-220°F (93-105°C.)
I lost the reference, but one source states: “An engine should never be driven hard until the oil reaches 120°F (49°C). The ideal operating temperature is 175-195°F (80-90°C). It can go as high as 265°F (130°C) for short periods but oil breakdown and excessive oxidation will take place above this temperature.”
Suzuki states, for example, that under racing conditions, oil should be kept at about 190-210°F (88-99°C) and that regular temperatures any higher should be an issue of concern. I don’t know what Ducati’s official position on this issue is, but I’m sure it’s similar.
[Edited on 10-21-2004 by Shazaam!]  |