I recommend the following based on my own limited experience and also upon the recommendation of my friend Jack Fischel, namely, the use of oil of wintergreen (Methyl Salicylate) as an additive to automobile motor oil and gasoline to keep your engine running smooth and clean.
If memory serves me correctly, I've used oil of wintergreen (OWG) on three cars: a 1971 VW bug, a hatchback (I forget the details on model etc.), and a 1991 Pontiac Sunbird. I added about a spoonful of OWG with each fillup of gasoline (first add the OWG then fill up the tank. I added OWG (also about a spoonful) to the motor oil immediately after every oil change service. Another thing that I used it for was the carburetor. With OWG in an atomizer, remove the air filter from atop the carburetor and with the engine running, spray (no more than a spoonful) of the OWG into the carburetor. I believe that I added OWG to my transmission oil in my Pontiac once after a mechanic had changed the transmission oil. In fact, however, the last two items (spraying into the carburetor and adding OWG to the transmission oil) I regard as extraordinary. If you wish to do these, I suggest you get help, especially if you have no automobile mechanic skills. Also they are not something you'd want to try when you drive up to a gas pump to buy gasoline.
I'm not sure just how religiously I have used the above practices with my cars but I'm sure I've done it sufficiently to get an idea how it works. I can say for sure that (following the above directions) I at least had no bad results. My automobiles have always run smoothly. I might also add incidentally that I've generally been good at maintaining my cars (e.g. changing the oil at recommended intervals, etc.). Of course other things like tires, batteries, radiators, etc. which are not affected by OWG and are subject to the usual problems and maintenance requirements.
I've found out is that there is a commercial additive product on the market which has an OWG smell to it. I believe it is called Marvel Mystery Oil. Occasionally I have used this product, following the manufacturer's instructions on the label.
I've purchased OWG at a pharmacies. Sometimes they had to special order it for me, and I have never needed a prescription. Just remember to use it with caution the same as you would when handling other hazardous chemicals.
At the moment, I do not own a car so I have discontinued experimenting with OWG. However, I would certainly start using it again if I were to purchase another car.Cautions:
"in pure form, methyl salicylate [oil of wintergreen] is toxic, especially when taken internally. A single teaspoon of methyl salicylate contains 7g of salicylate, which is equivalent to more than twenty-three 300mg aspirin tablets. The lowest published lethal dose is 101 mg/kg body weight in adult humans. It has proven fatal to small children in doses as small as 4 mL. A 17 year-old cross-country runner at Notre Dame Academy on Staten Island, died April 3, 2007, after her body absorbed high levels of methyl salicylate through excessive use of topical muscle-pain relief products," Wikipedia article on Oil of Wintergreen.