These tests were done by me to help determine the best products:

Background about tests:

As a worst case sample of material which might be found in gasoline I used ordinary tar. The brown deposits we find coating carburators, and which collects in fuel injectors and on intake valves, are the highest boiling components in gasoline. They are tar-like materials which distilled along with the lighter gasoline. The best solvent I've ever seen for these was methylene chloride, but it's expensive and I'm sure it's being phased out to protect our ozone layer. In any case, if you used it on a modern car the chlorine freed during combustion 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 these deposits from building up too much.

Dimethylformamide is listed in the 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 too toxic. Instead I used N-methyl pyrrolidone, which is also good.

For my tests, I tried to use a wide variety of products, well known and unknown, expensive and cheap, and also some pure solvents in order to represent a good cross section of products on the market. Note, carbon itself (such as soot and other 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 to release the heavy tarry materials trapped within them. However, some of these solvents are too harsh to use freely in the fuel system. (Someone in one of these forums told me that when the auto industry looks for good cleaners, they mostly look for solvents that will not attack the plastic and rubber parts in the system.)

Most cleaners (the safer & slightly less effective ones) usually have common solvents in them like toluene, 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 per 16 gallons.

Most of the straight solvents I used are at least as flammable as gasoline so be careful if you use them. The alcohol used was pure, 100% isopropyl alcohol. This has no water in it, it is not the same as "rubbing alcohol".

These test results are as fairly and accurately done as I could manage with the equipment I had available, and the other data presented is also accurate to my knowledge. Your car may have different plastics in it than mine does so if you choose to make your own cleaner, do it at your own risk.

TEST RESULTS

RELATIVE EFFICIENCIES AT WHICH VARIOUS CLEANERS WILL DISSOLVE HIGH BOILING RESIDUES FROM GASOLINE AND CARBONACEOUS DEPOSITS FOUND IN USED MOTOR OIL, (10=BEST):

ˇ 10 Gunk Gas Treatment
ˇ 10 Toluene (a common ingredient)
ˇ 9 Castrol Syntec Power System
ˇ 8 Duralube Fuel System Cleaner
ˇ 7 Gunk Fuel Injector Cleaner
ˇ 6 Redline SI-1
ˇ 5 Gunk Air Intake Cleaner
ˇ 4 Naphtha (a common ingredient)
ˇ 4 STP Fuel System Cleaner
ˇ 4 Seafoam Motor Tuneup
ˇ 4 Trak Fuel Injector Cleaner
ˇ 4 STP Intake Valve Cleaner
ˇ 4 CD-2 Emission Cure
ˇ 4 Prolong Fuel System Treatment
ˇ 3 CD-2 Fuel Injector Cleaner
ˇ 3 Techron Concentrate
ˇ 0.5 Butyl Cellosolve (a COMMONLY used "AUTO INDUSTRY DETERGENT" for oil and grease)

THE FOLLOWING CLEANERS DO NOT HURT NYLON (LISTED RANDOMLY).
(The letters in parentheses indicate how well they dissolved the material from used oil, A=best.):

ˇ Toluene (A)
ˇ 2-Phenoxyethanol (A)
ˇ Duralube Fuel System Treatment (B)
ˇ B-12 Chemtool (B)
ˇ Trak Fuel Injector Cleaner (C)
ˇ Techron Concentrate (D)
ˇ STP Intake Valve Cleaner (E)
ˇ Seafoam Motor Tuneup
ˇ CD-2 Emission Cure
ˇ Prolong Fuel System Treatment
ˇ Aromatic distillates
ˇ Naphtha
ˇ Butyl cellosolve
ˇ Acetone

THE FOLLOWING CLEANERS WILL DECOMPOSE THE NYLON SOCK IN THE FUEL TANK. Listed in order of increasing severity:

ˇ STP Fuel System Treatment
ˇ CD-2 Fuel Injector Cleaner
ˇ Gunk Fuel Injector Cleaner
ˇ Castrol Syntec Power System
ˇ Redline SI-1
ˇ Gunk Gas Treatment
ˇ Monoethanolamine
(The monoethanolamine is the worst here. It turns nylon black on contact. It is significant to note here that the "best" "detergents" in use today are similar, strongly alkaline organic solvents). Another use for the current bunch of organic amine "detergents" is cleaning deposits out of cylinders, so I hear.

I hope this takes the guesswork out of choosing good products.