slant 6 oil weight

I have not run 100% synthetic in my old cars yet. I currently use Rotella but I get zinc additive from the Summit store when I'm there and use about a half bottle per oil change. I don't have any cars with radical cams or high spring pressures so I'm not too concerned. However, I do know guys that have wiped their cams and they are typically more stressed engines than my junk.

My "modern iron" is a different matter. (if you call my 03 Neon every day driver modern that is) I switched to Mobil 1 about 15 years ago in all my new stuff. In the last 6-7 years though I've been buying the Walmart brand 100% synthetic. My son is a gear head too and he heard that supposedly the Walmart syn is made by Mobil. I don't know for sure. My reasons for running syn is that last month we had several mornings where the temp was below zero at start-up and I just want the oil moving quickly at those temps. Car sits outside while 3 60's cars are in the garage. Something like 90% of engine wear occurs in the first minute or so. I use 5W-30 in Winter and 10W-30 in summer. Also, I extended the change interval to 8000 miles and need to add a half quart at about 4000. As I get older, I like not having to crawl under the car as often. The engine internals seem to be cleaner when I take my junk apart. Neon has 208,00 miles on it in a bad climate and the cylinder compression is within 3 psi on all 4 holes so I ain't switching. I also use genuine Ohio-sourced air in my tires. Man that stuff really fills them up good.

Once the 225 is together, I'll probably use dino oil for 500 miles or so and then I think I'll try the Walmart syn. WTH, it may even be worth 1 HP and I need all I can get. I still have my suspicions syn leaks more than dino but the 225 will have all new gaskets and I'm hoping it will stay where it belongs. It does help keep the underside rust free though.
Just my 2 cents.