Short version:
Among all fuel system cleaners I'm aware of, Redline SI-1 contains the highest quantity per dollar (based on manufacturer MSDS) of the critical fuel-system-cleaning compounds known as polyether amines (PEA). Primarily for this reason I believe SI-1 to be the best available and most cost-effective fuel system cleaner product at retail pricing. .
In my case it has not been necessary to use Redline's recommended quantity of approximately 3 oz per fill-up. The effects of 1 oz per fill-up are indistinguishable in terms of tested results (see my basis for this statement below). This results in an approximate cost of $0.35/tank or less than a tenth of a penny per mile. A full case at this usage rate is enough to treat 180 full tanks of fuel or to last approximately 80,000 miles. (Figures based 15gal/tank, 25-35mpg).
Long version:
As far as I know, every effective fuel system cleaner on the market uses a class of compounds known as polyether amines (PEA), in varying proportions, to effectively clean deposits from fuel system components, and particularly from fuel injectors, which can quickly impact engine efficiency and performance when not operating correctly. My understanding is that these compounds were first developed by Chevron and sold under the Techron name, and have since been made available to other blenders of fuel treatment products. Until recently BG 44K, Chevron Techron Concentrate, Gumout Regane Fuel System Cleaner, Amsoil P.I. Performance Improver Concentrate, and Redline SI-1 (among others) listed polyether amines on their Material Safety Data Sheets (MSDS) in proportions varying from approximately 25% to 50%. Most of these products no longer list PEA on their MSDS, having changed their terminology to disguise the precise nature of their products' constituent components. Whether PEA is still contained in those products is a matter of uncertainty. As of this writing Redline's SI-1 MSDS still specifies that the product contains 30-50% PEA. Consequently it is one of the few remaining fuel system cleaner products that undoubtedly does contain PEA in significant quantity.
I have been able to test the efficacy of fuel system cleaners in one of my own vehicles using a method I stumbled on after having its injectors professionally cleaned while out of the vehicle. The car in question uses a Bosch engine management system that reports fuel injector data to an on-board computer, which then uses that data to calculate and report instantaneous and average mpg to the driver. I noted after the professional cleaning that the accuracy of the reported mpg, when used to measure average mpg over each full tank of fuel, improved suddenly from a prior error of around -3% -5% (that is, the reported mpg was ~3-5% below the actual mpg, or typically just over 1mpg low) to an error as close to zero as I could measure (that is, usually between -1% and 1%, fluctuating above and below a perfect "match"). This can be explained on the basis that the engine management system will compensate for a dirty injector by holding the injectors open slightly longer during each combustion cycle, in order to admit the proper amount of fuel. The on-board computer interprets that as a slightly higher rate of fuel consumption, reporting a lower-than-actual mpg figure.
After several thousand miles not long the perfect mpg accuracy I'd noticed began to deteriorate, likely indicating that the cleaned injectors were beginning to suffer from some sort of renewed impedance to fuel flow. Out of a desire to retain near-perfect injector performance, and also out of curiosity, I started experimenting with various commercially-available fuel system cleaners and keeping records of the results at each fill-up.
Leaving out the long details, I'll simply say here that the results were surprisingly clear and unambiguous. Each time I went several tanks without using a fuel system cleaner (usually as a result of simply forgetting to use it or not taking the trouble), the on-board computer (OBC) accuracy would deteriorate. This would fluctuate from tank to tank, of course, as a result of inevitable measurement errors, but the trend was very clear even over a small number of fill-ups. Returning to the use of a fuel system cleaner (Chevron Techron Concentrate, Gumout Regane or SI-1, all of which at the time did contain PEA), the accuracy would improve again very quickly within 2-3 fill-ups. I began using the SI-1 exclusively seven months ago based on its apparent cost-effectiveness and since then I have reduced the quantity I use in each tank to the current 1oz per ~15gal fill-up. The results remain unambiguous. If I use this small amount of SI-1 consistently, the accuracy of the on-board computer is excellent, with an average error of below 1%, or a fraction the error rate seen when not using such a product.
Based on the above I feel I can confidently conclude that SI-1 works very well, even at reduced treatment rates, at keeping fuel injectors clean. Fuel system types and injectors will vary, and other parts of the fuel system for example intake valves and combustion chambers might benefit from higher treatment rates (or, conceivably, might not benefit at all). Actual engine efficiency will not vary nearly as much as injector cleanliness, since the engine feedback system normally corrects for imperfect injector flow rates. However, as the flow is more greatly impeded, or impeded differentially among the individual injectors, mpg will be affected to some degree. I feel it is well worth the tiny cost to consistently use a small quantity of SI-1. Other benefits, such as to combustion efficiency as a result of combustion chamber cleanliness, to volumetric efficiency as a result of intake valve cleanliness, and to fuel system lubrication, probably exist as well although I can not evaluate them and have not attempted to do so. Other fuel system cleaners may work as effectively, or nearly as effectively, but I do not believe them to be as good in terms of value per dollar spent.
In my experimentation I did try some less expensive fuel system cleaners, those not containing PEA. They appeared to have no effect. I can not categorically state that only PEA-containing fuel system cleaners work, of course, but my observations did match the conventional wisdom on this point. I also experimented with using top-tier fuels only, without any additional fuel system cleaners. The results were the same as when using non-detergent (Costco and others) fuels. I don't doubt that top tier fuels contain small amounts of cleaners and will keep a fuel system functionally and acceptably clean, but the quantities involved are reputed to be tiny and my observations seem to indicate that even a small amount of additional additive is far more effective.
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My '06 Civic SI has about 40,000 miles on it. It had been getting around 22 mpg (mostly city driving) but even with long distance freeway driving (around 75mph) I'd only get about 23 mpg. I usually use Chevron or Shell gas. I also have used Techron fuel cleaner in the past with no results.
So I used Red Line SI-1 a few tanks ago, and my gas mileage has increased to about 26 mpg for my last few tanks. Right now I'm at 318 miles on one tank of gas, and i have one bar left on my fuel gauge (it's digital). Prior to the Red Line the best I'd ever gotten was 312 on one tank of gas, and that was after driving the ENTIRE tank on the freeway, and driving 10 miles with no bars left on the fuel gauge. Typically I would get 250-270 miles on one tank.
I'm stoked!
I will admit that using this stuff ain't going to do anything to help you if your injectors aren't clogged... but if you suspect they are, this is the fuel cleaner to get!
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Gotta give credit where it's due!
Wifey's car had a light ping/knock under throttle, so looked into Sefoam, etc. I am generally not a fan of the various `snake oil' products and do not routinely use any of them.
But I had read on forums of good results using various injector cleaners and such, so gave it a little research.
I've had good results with other Redline products so decided to give this bottle of joy a try.
Results were impressive and unexpected
One ran 6oz in about a gallon of gas in the wife's car Protégé5, 2.0l 4 banger, 125k+ miles. Knock went away within a few miles, quite impressive.
Two ran 1oz in 3oz fuel through 2 identical 15yr old 2stroke motors (weedeater/edger). I'd taken care of them over the years but never did a carb rebuild or anything. Carb screws had been adjusted way out over the years to get them to run. They were running, but very rough. Both motors started smoking like heck, birds falling out of the sky. It cleared out after a few minutes and kid you not, both are now running almost like new. I had to completely re-adjust the carb screws almost back to factory stock.
Three ran 6oz in the last gal of gas in my 1990 Mazda RX7. The traditional hot start issue (large, slightly leaky injectors flooding the engine) almost 100% gone! Now that was weird. Injectors have 4yrs and 8k since clean and balance, hot starting had been getting problematic. Folks do all kinds of things to these cars to work around the hot start issue, but this was sure easy.
I've not checked MPG change on either vehicle so no feedback there. ALL FOUR engines showed noticeable, quantitative benefit from use.
Recommended!!
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I can echo what Glenn said in his review. I started using fi cleaners back in the early 80's. A new Volvo 242 I had purchased new was starting to perform sluggishly. Another owner recommended a fi cleaner which I tried and it worked pretty well. Over the past 28 years I've tried just about everything on the market. Some worked well, others didn't. The Red Line SI-1 works better than the others I've tried. The BG cleaner works well too, but at three times the cost.
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In short, I put two bottles into my car and the mileage went up about 10%, which I am very happy with.
Long version:
I have a 2004 Infiniti G35 Coupe 6 Speed (Manual) that now has about 76000 miles on it. The car has some modifications (cool air intake, lightweight pulleys, lightweight flywheel) that could affect fuel mileage, but theoretically they shouldn't (or at least not much). All maintenance is done on time car is well taken care of.
Either way, my car is rated to 19/26 city/hwy, and I drive a combination of approximately 35%/65% city/hwy (this is actually conservative, the highway distance is probably more), but was only managing 17.5-18mpg per tank on average. I never expect to get the full EPA ratings since I drive faster than 65 on the highway and don't have a feather light foot when driving around town, but I didn't expect it to be THAT bad.
So I was reading around on the multiple car forums I'm on, and was recommended this stuff. So I went ahead and bought 3 bottles of this stuff. I put one in our truck (2009 Dodge Ram 1500 w/ Hemi) and 2 bottles in my G35 (I put one in when I filled up, and the second the next time I filled up).
With my driving style being the same, my mileage has gone up now to about 19.5-20mpg, which is a pretty solid 10% increase. I held off on posting but I've put at least 20 tanks through my car since I used this stuff and the mileage increase is holding steady (if not getting better). As far as I know I have not done anything else differently that may skew my results.
I haven't been monitoring the truck's mileage and since it gets driven by many different people I can't comment on the difference on that vehicle, but so far it's made a difference on my car. I'll probably end up throwing a bottle or two of this stuff into my car every 5-10K miles. Before anyone argues that you spend more money that way, at the mileage increase I got, I'm saving nearly 28 gallons of fuel every 5000 miles. Gas costs about 3.25 a gallon where I live (car takes premium) so that's over 90 bucks worth saved for spending 10-20 bucks on this stuff. Seems logical to me.
