I put a newer model 250 in my '59 that runs pretty low oil pressure anyway. I started using 20-50 weight oil in the summer to increase the oil pressure. When I started it on the first real cold morning this winter it acted the same way as yours did. I changed to 10-40 for the winter and have been using a magnetic oil pan heater on cold nights and it has solved the problem. My engine only runs about 25 lbs.pressure when warmed up and going down the highway and less than 10 lbs. at idle but it isn't using any oil so hopefully I can get another year or 2 out of it. One nice thing about it is that most people throw away 250's and replace them with V8's so they are cheap to replace. 235's aren't that easy to come by though.
