>Well... I still put STP in my old stuff.
I used to - until I tore into one of my motors after a few years of using it. No more LOL. Straight oil, zero additives. VR-1 racing oil is the go-to for the race cars/hot rods. Valvoline synthetic for the daily drivers.
I have actually used Trans-X on a C4 that was having some "cold start" issues of no going into gear reliably when dead cold. It actually helped. It was recommended, I called "BS" but what the heck - hey, look at that.
Pyramid Seal - 0.99 packet of metalicized pepper used to work great for fixing radiator leaks. Your radiator was on borrowed time after that, but it dang sure worked. I've seen two packs seal a crack in a lower hose mount that should have been welded. Don't think you can even buy it any more.
Moroso Ceramic Seal - works, had it seal a 1" exterior block crack for an entire race season until I could pull the motor and pin the crack. Used a lot with aluminum heads to seal any porosity.
Berryman's B-12 - works good as take additive for an older car that might need some carb attention. Sometimes. Works well to loosen gunk in a sluged up motor - provided you are about to pull the pan/covers/intake and replace things like oil pump, lifters, etc. Have used it more than once to save a lifter tick or two for someone that needed a few more miles. 1 pint in the pan, run till full temp, drain and change oil and filter.
Advertising works. When I worked the counter we sold a lot of STP, Slick 50, oil fowlers - anything the public got a mind would fix some issue that they would rather not face head on.
I found that the powdered copper in a liquid suspension (sometimes powdered aluminum) that used to be sold, long ago, only at truck stops really worked to plug coolant leaks. Today, most auto supply stores sell a version of either.
Forgot too that Marvel Mystery Oil was a fav by many, ala' Rislone's Engine Treatment.
Heet gas additive worked for decades too to eliminate water in pure gas. Today, "ethaloled gas" as I call it takes care of any water.
Best additive? White gas!
Honest to God, in late '68 or '69, we had a fellow bring in an old '61-62 straight-six Ford Falcon with badly knocking lifters. Frank Kush, the Standard Oil Station owner, had us then teenagers remove the valve cover. Honest, the top end had so much gook it looked like a perfect mold of the inside of the cover, kinda' like a Jello mold!
We scrapped out all we could, slapped the cover back on, added 4 quarts of really cheap oil and 1 quart of white gas (kerosene). Frank has us run the engine at idle for 1/2 hour, back to the the rack, drain, new filer, rinse-repeat.....4 times!
Man, when we got done and removed the leaky cover for a new gasket, all lifter ticking was gone and the top side of the head did all but sparkle! 16 quarts of oil and 4 quarts of white gas did it!
