I'll just leave this here... Personally I'm thinking at 248 F your modern oil additives will be ruined and your oil will be like water, but what do I know. 1957 was before I was born and oil was probably so basic it could take these temps?
A decent mineral based multi-grade will tolerate 130C or more and a synthetic a lot more, but if we are running that hot there is something wrong – or soon will be. Those using SAE30 should start worrying way before those with a modern multi-grade. I was 6 years old when W.R. Jeans issued that service circular.
