Oil (or water) capacity has NOTHING to do with cooling ability. It only increases the "inertia" of the cooling system... if you dont have enough heat dissipation through the rad or cooler, you will still overheat. A larger capacity will simply mean it takes longer for that to happen, but it WILL happen.

***** David, I agree with every word. However, it is that "inertia" that you refer to, that will get you to top of climb into the cooler air at , say, 5000 feet, and hence higher speed and lower power, without hitting the red line. I have noticed this effect in high ambient temps in summer as compared to cooler times of the year. Most of the year I can fly with as little 2/3 oil capacity no problem; but on a hot day,say, 90 - 100F ambient, I must have a full sump to avoid hitting the red line at 230F, in the climb. FWIW, Dave McC