Under the topic of 'those with more than 150,000 miles, there is this post: "1968 Nova, 250 six cylinder, 3 on the tree, 2.73 axil ratio, 155HP, max [email protected] RPM, bought new from Joe Moss in Albemarle, NC. Joe was 60 and lived with his mother. He said to run the factory oil for 5000 miles then use straight 20 weight oil. Ran 20W Kendell for first 150,000 miles. Used a quart every 1,200 miles. Put in a Frantz oil filter at 110,000 in 1972. By 150,000 miles, 20W was harder to get, and the store did not have 10W-30, so wound up with 10W-40. When the engine was hot, it ran like it was full of glue. Hummm... Lower fuel mileage, too. I went to an oil supplier and secured some straight 10W. Ran that to 250K miles and about 25 year old car at that point. The straight 10W oil increased my 10,000 mile average MPG by 1.9 MPG to 25.9 MPG. Blow-by and oil consumption started up. Got careless about oil changes. At 325,000 and 30 years, rebuilt the engine myself. About half the compression rings were stuck. All the oil control rings were caked in carbon. The oil control ring drain holes in the pistons were packed with carbon and could not be pushed out by hand and not that easy to drill out. Took 0.040" to clean up the cylinders. Crank miked new. Rod and main bearings had more corrosion damage than wear. She has 361,000 on the clock, now, but the new cam has a 2400 RPM peak torque and is harder to get a load rolling than the old cam. I get whatever 5W-20, yes 20, name brand oil is on sale and PureONE filters. The Frantz by-pass filter gets whatever 2-ply tissue we are running in the john. And, two ply makes a difference!" If I'm reading this right, it puts the debates that occur here on viscosity in perspective. I mean, there are still a lot of people on this forum who think 5W-20 is too thin to run in a modern engine, and those who even think a 30wt-oil is too thin, and run 40-wts. Yet here is someone who got 361,000 miles (580,000 km) on straight 20 and 10 weight oils, in a carburated, heavy, iron straight 6 from the 1960's! I'm aware that the engine was basically trashed at the end, but it still ran, and how many people actually put this much mileage on an engine. I guess my point from all this is that no-one should really worry about running 5W-20 oils, and that it may be a good idea for more people to run them, because the motor will survive, and a person will get better mileage for the life of the vehicle using them. At the same time, they are more expensive, so this savings may be cancelled out. But when they become as cheap and plentiful as 5 and 10W-30 weights....maybe! Any thoughts on this?