I went by YOUR post. At one time or another you were mixing oil, so it IS about mixing oil and using cheap assed oil.
You might not like my response but I don’t care. Playing tribologist is a bad thing.
Buying cheap assed junk oil is a bad thing. It sounded to me like you at least thought you killed an engine by using junk oil.
This isn’t for you. This is for guys who come along later.
DO NOT MIX OIL.
DO NOT BUY CHEAP JUNK OIL.
I did not know about the continued use of zinc, especially when people claimed it fouled up the catalytic converters. That is interesting.
As I have read, including from some of the Mopar manuals, the synthetic oil that they came up with in the 90s was pure synthetic oil.
At some point they began to blend it, and there was pushback to that.
At some point in time within the last two decades, the oil companies petitioned the government to allow the synthetic oil being sold to be a synthetic blend, instead of pure synthetic oil.
I want to say that the Mopar manual said Purr synthetic would last around 50,000 miles, except for the fact that it gets dirty.
Before I learned that they stop adding zinc or that they reduce the zinc content in oil, I was adding Mobil One 10W40 with the autoparts stores’ zinc additive. I didn’t flatten the tappers yet on the 1973 340 but maybe this mixture might be hurting my cam lobes.
As for mixing oils. I have done that with low performance, older or new high mileage engines that I had to maintain for a company that I worked for where the employees didn’t drive hard with the gas pedal, but neglected the hell out of the vehicles.
As I was told to do, not by choice.
Those trucks had transmission problems long before they ever had engine problems.
A coworker told me that his ignorant son changed his oil (90’s car) and filled it with automatic transmission fluid. He drove around for a week before his father corrected the mistake.
If ever there was a problem mixing oils, THAT WOULD HAVE BEEN IT. The engine didn’t die, but it probably aged 80,000 miles. Pretty sure that was a roller engine though.
Obviously that isn’t the same as mixing 0W20 with 20W50
As to testifying that synthetic can handle temporary, extreme heat compared to the ranges of mineral oils:
I drove 1990 Subaru Loyale with cheese and a stick shift. The manual transmission leaked to empty going through the hills of Tennessee. When I smelt something and saw the temp gauge climb a little, all I had in the car to add to the reservoir (GEAR oil) of that transmission was 10W30 Mobil One oil. The 4 cylinder car’s transmission reservoir was empty. I added 2 1/2 quarts of Mobil One 10W30 oil.
It worked.
I added gear oil when I finally came to a truck stop, 75W90 right on top of it and the transmission never had a problem. I don’t think that solution would work the same way with an engine, but it doesn’t seem to be catastrophic, it probably speeds up wear and tear.
