Oil doesn't provide a lot of cooling, but a minor amount, with friction reduction being the significant point. The methanol in the fuel is where one gets a significant cooling effect.

Years ago a Swedish company made the Damo 2.18 twin cylinder four stroke engines. The engines were designed to run without oil in the fuel. Just straight methanol for the fuel, no nitro and no oil. The methanol provided the lubrication as needed. But after they sold a number of engines, people were reporting problems with the engines. So they eventually started suggesting to use 1% oil in the fuel. But they did make quite a few prototype engines of which they had modellers use, test run and fly; and those engines did quite well without oil. So maybe it was a user issue at the time. The engines use needle and ball bearings on everything.



ref http://www.rcgroups.com/forums/showthread.php?t=1851088