I had a thought for you, small block chevy engines like the one on my El Camino have looser tolerances than today's engines, meaning that with today's engines they can easily clog up with junk inside the engine. That is why it is so important for people with newer vehicles to use Auto-Rx. My 1983 El Camino is speced for 10W-30. I think that everything from the early 1990s on up is speced for 5W-30 or now even 5W-20. I know this is true because I have read many owners of Crown-Vics that are speced for either 5W-30 or 5W-20 have used 10W-30 and have had issues at about 100,000 miles with oil consumption or oil burning. Many of the engines out now are overhead cam engines, whereas my small block has the camshaft below the cylinder heads.

I once asked a knowledgeable mechanic what is the 1st thing is to go on a small block, and he said the rockers because they are at the top of the engine, and when crud builds up, there is insufficient lubrication to the top end of the motor. I guess my point is that with Auto-Rx, it will keep the motor clean so there is SUFFICIENT lubrication to the top end.