Depends, many probably don't do much but just a snake oil gimmick. Some might really be useful but need to use regularly like every 5k km. From what I read, those that can work should contain a chemical called PEA (PolyEtherAmine) coz that's the only cleaning agent that can work in such high heat and pressure of the combustion chamber. Cleaners that I saw have this chemical are only:
- Gumout Fuel System Cleaner. I have been using this quite often coz it's the best value for money at only rm16 in ACE.
- Redline Complete Fuel System Cleaner. I used this long time ago and supposed to have the highest concentration of PEA but price is the most expensive now.
- 3M Fuel System Cleaner, quite expensive too at around rm40 if not mistaken.
- STP Fuel System Cleaner (silver bottle, not the normal orange injector cleaners), around rm30-40/btl.
- Caltex Techron cleaner, not sure how much now.
Others don't state if they contain PEA.
Last weekend I just tried Chemlube. It doesn't state to have PEA but it's supposed to enable water contamination in the fuel to get burned off so I try it. Price pretty expensive at rm50/bottle.
Theoretically though all our fuels should have good cleaners included so not sure how much more effective is an additional bottle is.