Do you have a favorite brand of crankcase motor oil? It's good to stay with one kind/brand of oil. When different brands get mixed together bad things can happen when the dissimmilar detergents react with each other. For years I stayed with Pennzoil. Then I saw a side by side comparison between Pennzoil and Valvoline. Valvoline is many times slicker than Pennzoil. So from now on I'll stay with Valvoline. What say you?
Because the chevron reps give us free stuff for buying so much.
Also, I wouldnt worry about mixing oils, as long as they are both the same weight and grade, you are not going to damage your engine by mixing them.
Why do you need to go rebuilding just because its using oil? If its not leaking (which is the first thing you should check) just give it some new rings and liners.
Mixing brands of oil isnt going to kill your engine.
It depends on the engine as to what you can get away with. Fine built engines with specific oil requirements tend to be very oil specific and using a different oil can cause damage or shorten mechanical life. As far as the big 3 go, Ford, Chevy, and Chrysler. I have found that the big v8s are very forgiving and once worn, they will accept almost any oil.
I had a worn out Chevy Small Block 350 in a 1970 Pick Up truck. I had restored the truck all but the engine. I had purchased a spark plug cleaner because it would oil foul the plugs in less than 1500 miles, and was using a quart about every 1000 miles between the leaks and worn out rings and valve guides. I was working as a mechanic at a Toyota dealership at the time, and motor oil was always charged to the customer, or the employee, and dispensed by the quart. The gear oil and transmission fluids were free, so I used to pump gear oil a quart at a time into the crank case just to keep it full. Helped the oil pressure, and the plugs didn't foul out as much.
When I finally had a motor rebuilt and ready to go in, I tried to blow up the motor that was in it, by holding it in low gear and flooring it down hills close to home. Tried for about an hour and a half to blow it up, and couldn't. Gave up and drove home, let it cool off, and pulled the worn out motor and replaced it with a fresh rebuilt engine.
So as far as mixing oils go, in something new, or precision built....NO, stick with the same brand, viscosity, or what the manufacturer recommends. As far as beaters go, anything that will pump, don't worry about weights, brands, or types, they are all good!!