I've seen and personally talked to several owners of small block based engines that mention high
oil temps. I don't know, but I'm getting a hunch that small blocks run hotter
oil temps, generally speaking, than big blocks do?
Is it possibly because of smaller
oil pan capacities? The cases that I'm specifically aware of were not large capacity pans. My pan, with filter, holds about 11 quarts, most of the time it's all I can do to get the oil temp up to a reasonable amount. I don't run a cooler, nor would I want too! Even running the engine HARD on a track it might get up to 100 c, on a hot day, thats as high as I've ever seen it.
"Rule of thumb" seems to be 250 F is about as high as you want to go with oil temp, by the way. Over 300 F and it's bad news for sure.