I haven’t read all this thread, but I would like to add some points to the Slick 50 product. Maybe something was mentioned in previous answers.
Slick 50 is supposed to make miracles in your engine thanks to added PTFE (Poly-Tetra-Fluor-Etylen) known as Teflon (does saucepan sound familiar?
). Teflon is registered trademark of company DuPont which is the only one who can use this name. Others can use only chemical denomination PTFE. I would like to quote official declaration of Mr. J. F. Imbalzano, Du Pont executive regarding use of PTFE in engines: "Teflon in the form of oil additive is not suitable in the use in combustion engines. Company DuPont disavows the possibility to use this material in any engine"
Why PTFE doesn’t work?
1. PTFE can be applied only on extremely clean metal surface at high temperatures in vacuum. There is no chance to apply it on engine components by adding it into oil.
2. PTFE is solid substance added into oil in the form of microscopic grains. At the same time, PTFE is very soft and it has to be milled into microscopic grains. You can imagine that milling of a soft material is not easy, has to be done by temperatures of about -270 degrees and there are not many companies in the world to mill it to the size of 3-5um (AFAIK only DuPont can mill it under 5um). The grains in the Slick50 are much bigger, moreover have tendency to flock together, flock with carbon particles and are caught by oil filter (in worse case they clog oil channels. BTW milled PTFE contains also small amount of residues from milling stones – another solid particles in your engine oil doing nothing good.
3. PTFE layer is not very stable. Any housewife knows that on Teflon saucepans only wooden or plastic kitchenware can be used, no metal objects. Even if there was a layer of PTFE on cylinder wall, piston rings would destroy it very fast.
4. Friction coefficient of PTFE is higher as by modern engine oils. So without oil it doesn’t lower friction, but the contrary. You need oil to make a separation layer between metal surfaces. So even if there was a Teflon layer - for what reason?
5. Even if we imagine a miracle and PTFE would form a layer on metal surfaces in the engine, this layer would change the dimensions of the components. For example crankshaft slide bearings are extremely precise. In ideal case, there is always a microscopic layer of oil in the bearing and the crankshaft "floats" in the bearing in the oil, with no metal contact. Add PTFE layer on crankshaft and the bearing and even if it is only 2-5um, it reduces the space for oil layer that is crowed out - wear rises.
6. Little amount of PTFE with the engine oil can get into the combustion chamber and be burned there. By PTFE burning Hydrogen fluorides (HF) are produced - highly toxic gases, not really something you want to come out of your exhaust. Some sources even say Phosgene might be produced which was used as a chemical weapon - military designation CG. Others deny this, so I am not sure.
Good thing is, that PTFE is chemically indifferent and will not destroy the balance of oil additives in the engine oil. It’s just particles floating in the oil and doing nothing good (it just clogs oil filter in the best case)
A little of common sense as an end line. There are a lot of oil treatments like Slick 50 on the market. Some contain PTFE, some metal particles like CU, Pb, or Ag, some are based on ZDDP (zinc dialkyl dithio phosphate), some contain normal engine additives just in different concentrations, other contain fluoride or chlorine as high-pressure additives, there are treatments based on ceramics…. Quite a lot of people is making business of this. Do you think that if something really worked well in the engine, the big oil manufacturers with extensive research and testing background wouldn’t use it? Why Texaco, Shell, Castrol, BP, ELF, Mobil, OMV, Q8, Selenia, Total, Valvoline and others don’t use any of them? If you care about your engine, change oil more often but don’t put anything in it.