I'm already running 20-50, so I can't really go up on the viscosity. The crank isn't banging in the bearings yet, it just looks like the engine is idling rough. There is no metal in the oil yet, so I don't think the crank is damaged. I also feel confident the engine will last another few thousand miles, it's only rough at idle because of the low oil pressure. My plan was to pull the crank, measure the journals, go to GM, and buy whatever undersize it would take to put me within spec. Then, I'll start saving my money for a rebuild. Chances are, the engine will run worse if I throw a cheap rebuild in there. It starts withing 1/4 turn of the crankshaft when it is cold - part of the reason I am concerned because the engine is starting before it can build oil pressure. It makes plenty of power to get me over the steepest of hills. It cruises at 3300 rpm without overheating on 100+ degree days with a partially rotted radiator. It passes smog with 22ppm hydrocarbon with an allowable 350ppm. And, finally, the motor has been rebuilt once already, so it is probably at a .030 oversize and I hear factory 350 blocks don't like an .060 overbore. It is such a nice block, though, and I don't want to throw it away - 4-bolt mains and possible high nickle, high tin.