I use 30 wt. non-detergent oil in my '29 Chevy. The motor is original (not rebuilt) and had non-detergent in it when i bought it. My '31 "A" roadster
uses 30 wt. detergent oil. Has an original (not rebuilt, as far as I know) "B"
block in it. The Chevy has no filter system with the '31 roadster having one
of the "by-pass" filter systems. I was under the impression that non-filtered
oiling systems used non-detergent oil. So any contaminants in the oil would drop out into the pan before the oil was recycled back through the engine.
And detergent oil suspends any contaminants within the oil so it can be picked up by a filter. I don't know how true these are, but they are what I go bye. I also use STP in both cars.
Bob-A
