On modern vehicles, the fuel system is essentially sealed and should stay as clean as the fuel that is put in it. But that’s not always foolproof, and inevitably some sediments and contaminants wind up in the system, which can get sucked up into the pump and circulated throughout the fuel system. The main danger is that the fine passages in the fuel injectors can clog, which interferes with the injector spray pattern and the fuel volume.
There are a couple of different ways to do a fuel system cleaning service, and they can be done together or separately. The first is the simplest, involving an additive that is poured into the fuel tank. There are numerous products available, which are all more or less solvents, that are added to a tank of gas. The fuel pump itself then circulates the cleaner through the fuel system. This can be called a fuel system cleaning service or a fuel injector cleaning service.
The second kind of fuel system cleaner addresses deposits in the intake system; from the throttle plate to the intake runners, to the intake valves and the combustion chamber itself. The intake system is prone to sooty or gummy deposits from various sources. Dust enters, depending on how efficient the air filter is; oil enters from recirculated crankcase vapors; and both can bake down to carbon toward the end-point in the combustion chamber where high heat is encountered. Cleaning the intake system is intended to remove gummy deposits and carbon build-up.The simplest method uses a pressurized canister to spray a cleaning solvent into the intake system while the vehicle runs.
Costs of Fuel System Cleaning
This fuel system cleaning service is typically done at a fixed price, regardless of the make and model of the vehicle. To do a simple gas additive service, the average cost is about $50 to $80. This is often done in conjunction with a scheduled service interval and bundled in with other things, such as inspections and fluid changes.
The more involved intake system cleaning service can cost between $150 and $350. There are various different brands of products available and various kinds of injection methods. In many cases, the two kinds of services are done at the same time, again for a fixed price of $150 to $350. The products themselves are fairly inexpensive.
How Effective is Fuel System Cleaning?
That is a contentious question. A gas additive that you pour into the tank can be effective. There are some more advanced methods of cleaning injectors that have been around for awhile, where the injectors are removed from the vehicle and mounted in a fixture where they can be run and their spray pattern inspected. If there are problems, then solvents can also be run through them until the spray pattern is as good as it should be. This kind of device isn’t common, but it’s the kind of thing that prompted the development of fuel additives to clean and maintain injectors. There is some objective research that shows a benefit to miles per gallon and emissions if those were being harmed by an injector spray pattern issue. Applied as preventative maintenance, the ideal is that you’d use a fuel system cleaner to avoid problems rather than solve problems; done that way, no improvements would be noted.
Cleaning the intake system is a more laborious and tricky thing to do and less certain to be necessary. In normal circumstances, cleaning the throttle plate is periodically necessary, and is a normal part of a traditional tune-up. Most of the time, it’s best done manually (with solvent and a rag), but an alternative is to do it with an intake system cleaner. The result is usually not as good, and the cost is higher than an old-style throttle body cleaning.
Going farther in, various types of products do a reasonable job of cleaning gummy residue from the intake runners, but there is no real data that says residue in the runners causes actual harm. Farther from that, removing carbon from the valves and combustion chamber is one of the least supported claims. In most engines, the intake valves stay pretty clean because they are downstream from the fuel injectors and the air/fuel mixture itself cleans them. On a direct-injection engine, however, the fuel is injected into the combustion chamber itself, and the intake valves can be prone to a build-up of gummy residues and carbon. In that case, a fuel induction service is useful, and is often part of scheduled maintenance services.
Which is also to say to the initial question, “how effective is fuel system cleaning?”: opinions and results are mixed. The easy and inexpensive gas additive may be well justified, but the more expensive fuel induction cleaning spray is probably not worthwhile, except on a vehicle with direct-injection.
What Can Go Wrong with a Fuel System Cleaning?
There isn’t much to worry about with a simple fuel additive that goes into the gas tank, other than usually making sure there’s at least half a tank of gas so it isn’t too concentrated. But when doing the more involved work of spraying solvent compounds into the intake system, problems can occur if care isn’t taken. The vehicle is designed to burn fuel in a specific mixture, and adding too much cleaner too quickly can throw things out of balance, while also introducing a lot of liquid into the combustion chamber. Liquid doesn’t compress, so if it’s done too quickly, the engine can stall or hydro-lock, and in the worst case, it can bend a rod or cause other internal damage.
There are many intake systems where the routing of the runners allows fluid to collect, and an intake system cleaning compound can puddle up in the system if it’s not sufficiently atomized. Then, on sudden stops or starts, the trapped fluid can slosh forward into the cylinders, causing the engine to stall again or, in a worst case scenario, hydro-lock and possibly cause damage. Introducing the solvent slowly and giving it a good test drive afterward is usually sufficient care.
It is very common for an intake system cleaning to cause isolated misfires as it works and to trigger the engine light, but that should solve itself within a few miles, and reset with a couple of key on-off cycles. Sometimes a vehicle will go into limp mode, but that’s also solved by shutting the engine off and restarting.
On a standard fuel injected vehicle, there is usually no recommended fuel injection service. On a direct-injected vehicle, it might be every 30k or 50k; reading the owner’s manual maintenance information is best.
It is very easy for any vehicle owner to purchase a fuel system cleaner that goes in the gas tank and pour it in. Cleaning the intake system is more difficult, requiring some expertise and tools. It is possible to do it at home, but not often advised.
Following the owner’s manual’s service recommendations is the best way. The second best way is to track mileage; if the vehicle is suffering from poor mileage, but has no engine light or other indications of a cause, trying a fuel and intake system cleaning might be the least expensive first attempt to improve things.