A buddy of mine stopped by and gave me a bunch of filters and oil. now I have a few quarts of 30w non detergent. If i add 1 quart to top off a vehicle that leaks and burns a little oil will i hurt anything? The engine capacity is 6 quarts.
There are still a few applications for a straight mineral oil.
If you operate HD equipment equipped with a clay-cartridge oil cleaner, like a Clarifier Process, then a motor oil with additives will plug the clay cartridge. However, those sort of filters have all but disappeared.
Some HD manual truck transmissions require straight mineral oil to be compatible with seals and synchro's. Again, they have all but disappeared as most HD truck trannies like Eaton RoadRanger require/strongly recommend a synthetic 50 oil.
Some folks who run inboard marine engines still like to use a mineral oil. Same as some folks who mix for 2-cycle. There are far superior modern alternatives though.
Old beater is ok, if it's an old clunk, why bother getting good oil?