1. You should use an oil weight that is recommended by the mfgr.
2. If the engine has flat tappets then it will need a high concentration of ZDDP (zinc and phosphorous) which is almost impossible to find.
The oil that most diesel users grabbed for years was Rotella because it had the highest amount of the scuff reducers that high compression and flat tappets needed. Once the gubbment
legislated this out of oil, well very low amounts now, problems resulted as most oil mixers complied with the gubbment.
Now you will have to get an additive or run a synthetic to subsidize the needed elements for older engines.
NAPA got me some Rotella 30WT high performance oil that was "CF" rated. If you can get "CF" rated oil it will have the good mix for older engines.
The newer engines with all roller valve train don't need "CF" rating. A good 30WT oil is fine for the new engines.
Here is one additive that is supurb!!!!!! It has all the good stuff. If you have any old cars/trucks this stuff is what they need.
Well I can't find the pic of the bottle so I'll just tell you what it is..........GM "Engine Assembly Lubricant" formerly known as E.O.S. (engine oil supplement). EOS is on the bottle but that is the only reference as to the early product. It is virtualy the same but has been repackaged etc to satisfy gubbment garbage. Most any GM dealership has this in stock. If not they can order it.