@irlandes about 15 years ago I sold my 1970 Cadillac to a friend who was moving to Aguascalientes for several years to teach English. Apparently at the time it could be a lucrative business to be in. His reasoning for wanting the car was that he could do most of the maintenance and repairs himself.
The car burned and leaked a little oil, and his choice of 20W50 oil wasn’t always available at gas stations and mini-marts in the Seattle area, but the further south he got the more available it was. By the time he got to his new home, that’s all he could find.
Shell Rotella T6 synthetic motor oil, It is 5w40 so it has a very wide temperature range. It still has ZDDP because it is mean for diesels. The ZDDP will protect your camshaft and stamped rockers. It far exceeds the standards of the oil made for your Pontiac engine (and that 400 IS a real Pontiac engine, right?). And, it doesn’t cost very much at the big-box stores that sell it.
Many folks I know say 5-30 is a poor choice for flat tappet cams and prefer to use 10-30 instead. I have yet to meet someone who has experienced oiling issues with either so I just let it go.
The flat tappet cam debate. This started with British motorcycles and progressed into British sports cars as I recall. It eventually spread into early American cars. Engine rebuilders were getting very unhappy customers when after a rebuild, the cams in their engines would be completely flat after only a few miles (50 to 100 in some cases).
The engine rebuilders blamed the new oils that did not have ZDDP in it any more. The debate, at least at first, was not directed at 5w30 oil but all SM and newer oils. Since most of that was 5w30, I guess that some made that leap.
This kind of like what happened to Quaker State in the 70’s. GM recommended 10w40 Quaker State for their vehicles and most customers followed that recommendation. After the engines got tighter smog controls in 75, 10w40 began to sludge up in their engines. Any 10w40 at that time would do this, but most people blamed Quaker State because that is the oil they were using at the time and Quaker State lost status as a premium oil.
What most people in the discussion do not understand is the difference in metallurgy between older engines and newer ones. There are several but the one of most interest is the camshafts. The machines that used to grind camshafts (and crankshafts as well) back in the day could not deal with hard alloys of steel.
Cranks and cams used to be made of soft steel that was easy to machine and then case hardened. Eventually manufacturing processes, mostly the inserts used to do the cutting, were made harder and more durable. This allowed higher grades of steel to be used. With the higher grades of steel, the case hardening was not needed anymore.
Now a modern rebuilder gets an old engine from the 50’s or earlier and the cam lobes are worn down just a little. He decides to regrind the cam by removing material from the low part of the lobe, effectively raising the peak of the lobe, but he doesn’t case harden the cam when he gets through.
The metal now exposed is soft steel and it won’t matter how good the oil is, that lobe will wear down quickly. If the cam was worn down a lot to begin with, the rebuilder would have welded new material onto the lobes and then reground. The material welded on probably would have been a harder alloy so this may not have become a problem in that case.
