Originally Posted By: OneEyeJack
Are off the shelf solvent products that people pour into their engine oil considered additives? I see that a lot of people on this site write about one solvent or another and advocate pouring them in with engine oil. It's true. With the BITOG search function you can find an endless stream of these postings.
If you add it to your oil (or gas), that makes it an additive. Some of the oil additives are solvents - they may soften or remove sludge from the engine while also thinning your oil. Even popular products like Marvel Mystery Oil are primarily solvents (the name notwithstanding).
Some additives simply thicken or thin the oil - sort of like adding 1 quart of 0w-10 to 4 quarts of 10w-30. If thinning or thickening your oil (for whatever reasons) is your goal, you might consider starting with a thinner or thicker oil in the first place.
A few additives, like MoS2, actually interact with the metal in the engine - leaving a 'plating' on the moving parts - to reduce friction and reduce heat. Products containing PTFE (Teflon) are sometimes lumped in this category. Be aware that the maker/inventor of Teflon suggests that it has no place inside an engine, and several independent tests support this suggestion.
Thanks to the internet (and no thanks to the poor labeling of many products), it is usually possible to determine what is really in a particular additive - what ingredient might make a difference. You should do your homework before spending money on any product, and particularly before dumping some "unknown-ingredient product" into your engine.
Regardless, they're all 'additives'.
