Read it for what it is worth
http://forum.doityourself.com/showthread.php?t=74032
Yes, I did do a fairly scientific comparison of the cleaners, as much as I could do in my house, but I am a chemist with experience in the petroleum industry. Here's a summary of my results:
For the following tests, I tried to use a wide variety of products, well known and unknown, expensive and cheap, and also some pure solvents. Note, Carbon itself (such as soot and thermally decomposed material is not soluble in any solvent but solvents like dimethylformamide and N-methyl pyrrolidone do a good job of breaking up clumps and dispersing the fine particles but some of these are too harsh to use freely in the fuel system.
Relative efficiencies at which various cleaners will dissolve high boiling residues and carbonaceous deposits found in used motor oil: (10=best)
10 Gunk Gas Treatment
10 Toluene (a common ingredient)
9 Castrol Syntec Power System
8 Duralube Fuel System Cleaner
7 Gunk Fuel Injector Cleaner
6 Redline SI-1
5 Gunk Air Intake Cleaner
4 Naphtha (a common ingredient)
4 STP Fuel System Cleaner
4 Seafoam Motor Tuneup
4 Trak Fuel Injector Cleaner
4 STP Intake Valve Cleaner
4 CD-2 Emission Cure
4 Prolong Fuel System Treatment
3 CD-2 Fuel Injector Cleaner
3 Techron Concentrate
0.5 Butyl Cellosolve (a commonly used "auto industry detergent" for oil and grease)
These cleaners do not hurt nylon (listed randomly) (letters in parentheses indicate how well they dissolved crud from used oil, A=best):
Trak Fuel Injector Cleaner (C)
STP Intake Valve Cleaner (E)
Techron Concentrate (D)
Duralube Fuel System Treatment (B)
Seafoam Motor Tuneup
B-12 Chemtool (B)
CD-2 Emission Cure
Prolong Fuel System Treatment
Naphtha
Aromatic distillates
Butyl cellosolve
2-Phenoxyethanol (A)
Toluene (A)
Acetone
The following cleaners will decompose the nylon sock in the fuel tank - listed in order of increasing severity:
STP Fuel System Treatment
CD-2 Fuel Injector Cleaner
Gunk Fuel Injector Cleaner
Castrol Syntec Power System
Redline SI-1
Gunk Gas Treatment
Monoethanolamine
(The monoethanolamine is the worst, and it is significant that the "best" "detergents" in use today are similar, strongly alkaline organic solvents. Someone in one of these forums told me that when the auto industry looks for good cleaners to use, they mostly look for solvents that will not attack the plastic and rubber parts in the system.)
(Note, when the nylon decomposes it forms a gooy substance which is not soluble in gasoline or other organic solvents usually used to clean out the fuel system. It is very soluble in water so you have to clean your tank, fuel lines and injectors with water, alcohol or some other similar solvent. If you use "pure" gasoline, the goo will stay in the gas tank but if you fill up even once with gas that has alcohol added, the alcohol will flush the goo throughout the entire fuel system. Expect to pay a few thousand dollars to the mechanic as he tries to figure out what keeps plugging up the new injectors he'll have to install.)
Dimethylformamide is listed in literature as being a good engine cleaner and is "especially good at dissolving carbonaceous deposits". I haven't used this myself because it is a bit more toxic than N-methyl pyrrolidone.
In the tests, actual carbonaceous solids were used that had accumulated in my oil. I use Mobil 1 5W-30 which is more resistant to formation of these materials than most other oils. I have a large container I put old oil into and for the tests I scraped up the gunk that had settled to the bottom of the tank.
Also, the brown deposits that you see coating carburators, and I'm sure collect in fuel injectors and on intake valves, are the highest boiling components in gasoline. They are tar-like materials. The best solvent I've ever seen for these was methylene chloride, but it is expensive and I'm sure is being phased out to protect the ozone layer. If you used it on a modern car the chlorine freed from the combustion temps would corrode the oxygen sensor. Amoco advertises a cleaner gasoline and I'm sure it's because they've reduced these tar-like compounds. All gas these days contains at least a little detergent of some sort to help keep deposits from building up.
Another use for the current bunch of organic amine "detergents" is cleaning deposits out of cylinders, so I hear.
One more thing, most cleaners (the safer & slightly less effective ones) usually have common solvents in them like toluene and other poly-methylated benzenes, alcohol, acetone or methyl ethyl ketone, and naphtha. If you want to use these to clean your system, you can get more for your money by buying the pure solvents at a hardware store and mixing them yourself. I have never had a problem adding toluene, acetone, alcohol, or naphtha to my gas tank in quantities up to one quart/16 gallons.
FYI Duralube uses naptha
http://hpd.nlm.nih.gov/cgi-bin/household/brands?tbl=brands&id=4006003
Going to bed, enough of this for now...
