My past experiance over the last 25 years would offer this opinion;
I have found no problems in using modern "straight" weight oils in the engines I have been operating, be it GM 4s, 6s, Ford 4s, 6s, and V-8s. I try to change oil on a regular basis and use 30 weight. The vehicles I operate are not driven very hard and as I approach my 73rd birthday, they tend to be driven only in fair weather.
