I’d bet most of you used STP back in the day (60’s-70’s) and had your hopes of a rebuild in a can destroyed. As I’ve said many times, the additive package of new and used oil is important.
The lab test and abrasive tests are useful. The shot lawnmower on 100% STP is stupid as well as the cold flow test.
https://youtu.be/mqiUFklL_XI

The Petroleum Quality Institute of America website is an excellent resource to find out what is in some of the engine oil, transmission and antifreeze coolants that you purchase.

https://pqia.org/

I know people who used STP to assemble motors
A Sticky gooey mess.
Mixed with some oil it was not to bad

Andy Granatelli owned STP and ran Indy cars
They gave away Tee Shirts and free cases of the stuff at the Nationals at Indy and other races
Everybody had those Tee shirts

Basically I think it was an oil viscosity additive used to thicken oils.....

I thought STP meant:
Stop Teenage Pollution

Used it for engine assembly lube in the late 60's and early 70's. No complaints.

Brief period it was just EOS and some engine oil mixed.
I mix Synergyn assembly lube and GM EOS about 50/50 for the past 25-30 years.
The Synergyn looks, smells, and feels a LOT like the original STP formula.

I never fell for the idea STP was a good additive though.
If I had an oil burner it got 50w oil.

quote:

Basically I think it was an oil viscosity additive used to thicken oils.....

I believe the pitch was a "viscosity index improver". "Viscosity index is a unit-less number that is derived by measuring a fluid's viscosity from 40⁰C to 100⁰C. The higher the viscosity index, the greater the stability of the lubricants viscosity". "The change in an oil's viscosity due to a temperature change is called the viscosity index (VI). Understanding VI is important to discern whether the lubricant in question meets the asset's requirements based on the operating temperature range". "The viscosity index (VI) is an arbitrary, unit-less measure of a fluid's change in viscosity relative to temperature change. It is mostly used to characterize the viscosity-temperature behavior of lubricating oils. The lower the VI, the more the viscosity is affected by changes in temperature. The higher the VI, the more stable the viscosity".

quote:

Originally posted by Goob:
Used it for engine assembly lube in the late 60's and early 70's. No complaints.

Brief period it was just EOS and some engine oil mixed.
I mix Synergyn assembly lube and GM EOS about 50/50 for the past 25-30 years.
The Synergyn looks, smells, and feels a LOT like the original STP formula.

I never fell for the idea STP was a good additive though.
If I had an oil burner it got 50w oil.

"I knew a guy" in the 1970s that actually used 90W gear lube in his crankcase. It worked, right up until the first cold morning. Take care. Tom Worthington