Andy Granetilli was paid to like STP, but many folks are advocates for various treatments without such encouragement.
Lubrication is a science, a bit of an art, and often a religion of sorts. Separating all those aspects can be a chore, and unless you are operating at speeds above 8000 RPM you may not need anything 'special' but it must be clean and free of water, fuel and other contaminants.
When I was at Autonetics in the 60's, the company was making guidance systems for the Minuteman missile based on gyroscopes that were spun up at manufacture and not re-calibrated over the life of the missile. These used gas bearings but still had lubrication requirements. Here is a summary of what was approved -- note STP was among the substances named.
Anecdotal examples abound on what can be done in dire circumstances with limited or unusual lubrication in an engine. There is the very persistent story of a 2CV Citroen running over a few hundred miles in the desert lubricated with nothing but bananas in the crankcase. While these stories do not mean that oil is optional in an engine, neither do they provide any reasons to believe that additives are required/essential...if you like these sorts of talisman approaches to drive off evil engine failure spirits, go for it.
Fuel additives are a bit of a different matter, and the wide prevalence of gas containing ethanol means we need to be vigilant in keeping water absorption at bay since the gel that forms is very bad for carburetors.
And while I had said earlier that no gas and water should find its way into engine oil -- it does turn out that some car engines like that in my 1957 DKW sedan absolutely MUST have oil in its gas (since it is a 2-stroke engine...)
Some more toward Tom's predicted "55 gallon can of worms..."
Viscousity, Chemical Stability, Sulfur content, API gravity, Neutralization number, Demulsibility, Oxidation Stability, Corrosion resistance, Pour Point, Flash Point, Fire Point, Cloud Point, Freezing Point.
Attached is a good summary of the various oil properties and what is important about them. Note that 'low friction' is not specifically one of them -- but there is a reference to one component that may be added which has its own drawbacks...
The sulfur content of lubricants is an important property to consider as the chemical element can fast-track corrosion. That said, sulfur can also be added to certain oils to improve lubricating capabilities.
Attached is the full document of some thirteen chemical and physical characteristics of lubricating oils as published by Petro Online recently...please excuse the British spelling of many words in the actual text. Be sure to read the reasons WHY these properties are important. Basically they include Reducing mechanical wear and friction, Minimizing asset maintenance costs, Extending the lifespan of assets, Reducing unplanned downtime, and Avoiding catastrophic failure.
I have nothing to add, scientifically speaking. But I remember Granny applying oil, about 1-2 tspns full, depending on the offense, to grandsons to cure their rowdy/rambunctious tendencies. Worked a treat.
I remember back when I was a youngster I had a 1958 VW and for some reason I don't remember I liked to put STP in in, most likely due to peer pressure (or advertising). Motor Honey it was known as, and when it was cold out (I am in the Midwest) it poured so slowly, like thick cold golden honey. Ah, the old days!
Here is my "Real World Experiance", I've run the crap out of engines all my life and have NEVER had an engine fail, blow up, stop working, etc ..because I didn't use an oil treatment. An engine needs Clean Air, Clean Fuel, and Clean oil, to last a long time. There's not an oil brand on Walmarts shelf that I wouldn't put into any of my vehicles. I am a believer in Fuel treatment for storage longevity but not snake oil for oil treatment. If you are adding an oil treatment to your oil, I suggest you buy better oil that you feel comfortable with without adding another $10 worth of additive. People who reference proven track records because nothing has happened since they use the additive all the time probably wouldn't have had any problems without using the additive, I know that's the case in my experience. When I was like 12 years old I ran a Sears riding mower as a toy popping wheelies and revving it as high as the bypassed governor would allow. I was a poor kid and I got used motor oil from the local gas station to burn in it since it did use oil and smoked... If an engine ever should have blown up due to bad oil, that was the one...lol Ya, Oil and additives are a lot like opinions on whose wife is the ugliest.....It doesn't matter.
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