Optimum temperature - V-twin

[ICman]

I'm involved in a discussion in another forum regarding motorcycle engine temperatures. Namely, a V-twin, air-cooled aluminum engine.

I say oil temperature (in the oil tank, not the engine) should run between 180F and 220F for proper evaporation of water and proper lubrication. Many disagree, and believe temperatures in the 140F - 160F range are better for engine longevity. Then, some references say that temps above 230F are not harmful, especially with synthetic oil, and that the engine should be fine until temperatures reach into the 300's. (I was running at 140F in an ambient of 102F.)

I know, from reading a previous post, that the perfect engine temperature depends on the engine, power output, etc. How does ambient temperature effect this? i.e., are we looking for a specific temperature, or a delta temperature (compared to ambient)?

I'd like to hear from an engine design engineer ...

Thanks,

. . . Steve

 

[dgallup]

Most of your air cooled motorcycle engines depend on the oil for a significant portion of their cooling. I think Harley just added piston cooling oil jets to their "new" rubber mounted Sportster motor. It usually only takes them 30 years to add new technology. So what I'm getting around to is that these engines want cooler oil than what is ideal for a water cooled engine.

There is no problem with oil temps up to 240F with conventional oils, above that the life is halved for every 10 degrees (approximate at best). 300F is OK in a race engine for short events.