Since the mid-1990s, all gasoline sold in the U.S. has been required to contain detergent additives to control deposits on the intake valves and fuel injectors. Here’s how detergent gasoline was originally developed back in the 1950s, what it’s supposed to do, what TOP TIER gasoline is, and why adding too much detergent can be as bad as not having enough.
The First Detergent Gasolines
Although detergent lubricating oils were developed for heavy-duty diesel engines before World War 2 and were widely adopted for gasoline engines after the war, detergent additives for gasoline date back only to the early 1950s.
The first detergent gasolines were developed to tackled the problem of carburetor gumming. An engine needs air as well as fuel for combustion; even with a high-quality air filter, there will be some contaminants in the intake air, which tend to leave sticky deposits around the edges of the throttle plate and in the idle air passages. Deposit formation is usually worst at idle, when the throttle plate is mostly closed and air around it is moving at high speeds. As deposits build up in those areas, they interfere with idle speed and vacuum spark advance, causing rough running.
In the early ’50s, carburetor deposits still weren’t a big problem for the average driver, but they were becoming a huge headache for taxicab companies. Taxis spend a lot of time idling and in heavy traffic, where their intake air becomes contaminated by exhaust fumes and crankcase blowby. Carburetor gumming became so bad for urban taxi fleets that they were having to adjust idle mixture settings every 5,000 miles and overhaul or replace carburetors as often as every 15,000 miles — way too often for high-mileage taxicabs.
In 1951–1952, the research arm of Standard Oil of California (Chevron), then called the California Research Company, did extensive work on combating carburetor deposits with different fuel blends and additives. After various unsuccessful experiments, researcher Jack MacGregor suggested that they try adding oil-soluble detergents to the fuel to wash away throttle body deposits. Experiments using the same detergents added to lubricating oil didn’t work very well, but the idea seemed promising, so researcher Maury Barusch devised a different type of detergent, long-chain alkyl amines, that proved to be remarkably effective at cleaning and preventing carburetor deposits. They then refined the chemistry to get the best results at very low concentrations, around 30 ppm.
Standard Oil of California began marketing its first Chevron “Detergent-Action” gasoline in spring 1954. They brought in several members of the California Research Company team to demonstrate the principle to sales executives using an 8-foot-tall transparent carburetor equipped with a smoke machine and vacuum generator to demonstrate how throttle deposits formed.
Chevron was followed by several other oil companies, including Texaco, which also introduced its own “Petrox” detergent additive for Texaco Sky Chief premium fuel in 1954.
Petrox was probably developed concurrently with the Chevron detergent, but Texaco was much less forthcoming about its development or even how it worked, describing it as a “petroleum-based” additive and a “new element.”
By the mid-1960s, many U.S. premium gasolines and some regular grades had detergent additives, although the composition and concentrations (“treat rates”) of those additives varied quite a bit, as did their effectiveness. Until the late 1980s, cheaper U.S. regular gas often had little or no detergent; in some other countries, regular fuel still doesn’t.
Different Types of Intake System Cleaning
It became clear even by the early ’60s that while detergent gasoline was useful, there was a lot of room for improvement. Early low-concentration detergent gasolines helped to prevent new carburetor deposits (which the oil industry calls “stay clean” or “keep clean”), but were of limited value in removing existing ones (“clean-up”), especially with the changes in average driving patterns. More Americans were now spending more time idling in stop-and-go traffic, and were running into the kinds of problems that previously had only been seen by cab companies and delivery drivers.
Emissions control measures created additional challenges. Positive crankcase ventilation, adopted by most U.S. cars in some form by 1963, reduced hydrocarbon emissions and crankcase sludge, but routed corrosive crankcase blowby back into the intake manifold, the air cleaner, or both, which tended to produce more intake system deposits.
So did exhaust gas recirculation, which was adopted on some cars from the early ’70s to reduce nitrogen oxide emissions.
While early detergent gasolines were developed specifically to reduce carburetor deposits, there was growing interest in using detergent additives to reduce the other types of intake system deposits to which gasoline engines were prone. In addition to throttle body deposits, many cars suffered deposit buildup in their intake manifolds, intake valves, and intake ports, which robbed performance, increased fuel consumption, and caused driveability problems that could be hard to fix. (One taxi fleet suffered such severe manifold deposits that the company resorted to removing the manifolds and trying to burn out the deposits with gas flame!)
Tackling these problems has required a succession of new engine-cleaning fuel additives. Although these are still often generically called “detergents,” since about 1970, the industry has also used the broader term “deposit control additives” (DCAs), since some additives are not technically detergents in a chemical sense. DCAs are usually part of an additive package that also includes rust inhibitors and fuel system icing inhibitors.
Developing suitable deposit control additives has been an ongoing balancing act. Fuel detergents and their carrier oils need to be storable and not react with rubber or plastic fuel system components. The ideal detergent additive needs to remain chemically stable all the way to the intake valves, but then needs to break down as immediately and completely as possible during combustion, without leaving residue in the combustion chambers or fouling catalysts or oxygen sensors. On top of that, gasoline distributors would really like all this to be accomplished at as low a concentration as possible, since high-concentration additives are more expensive.
As if that wasn’t challenging enough, the “additized” fuel needs to be compatible with a wide range of different engine designs and fuel systems, which have changed a lot over the years. Additives that worked well enough to for carbureted engines weren’t always well-suited to port fuel injection systems. Newer detergents that more effectively prevented injector deposits with port injection could increase intake valve deposits. Since the 1990s, detergent additives have done a better job of reducing intake valve deposits, but sometimes at the expense of increasing combustion chamber deposits, which (like “carbon buildup” in older engines) raise a gasoline engine’s octane requirements and can cause detonation and piston knock.
Regulated Detergents and TOP TIER
Considering that intake system deposit buildup can increase exhaust emissions as well as hurting performance and fuel economy, it took a surprisingly long time for detergent gasoline to be regulated in the United States. Even the California Air Resources Board (CARB) didn’t implement its gasoline deposit control additive rules until 1990.
By 1990, more than 90 percent of U.S. pump gasoline contained some amount of detergent or deposit control additives, and the federal Clean Air Act amendments of 1990 gave the EPA a statutory mandate to set regulations for detergent additives in gasoline. Even so, the first interim EPA standard didn’t take effect until 1995, and the EPA didn’t issue a final rule until July 1996.
The EPA now requires that manufacturers register all fuel additives, describing their ingredients and establishing “lowest additive concentration” (LAC) levels for fuel distributors to use. For detergent additives, the LAC is the concentration needed to keep intake valve and port fuel injector deposits below certain specified levels, as measured in standardized tests. The EPA still hasn’t established limits for combustion chamber deposits (although the current CARB rules do).
Gasoline sold in the U.S. for on-road or off-road use must contain at least the LAC of a registered detergent additive; it can have more than that, but not less. (There are exceptions for racing fuel, avgas, and R&D projects.) Contrary to popular belief, the EPA doesn’t mandate how much detergent gasoline must contain — the lowest additive concentration is determined by the detergent manufacturer. However, even in the 1990s, the EPA was criticized for setting the required performance standards too low, which allegedly led some additive manufacturers to specify lower detergent treat rates than they had been using before the regulations went into effect.
The EPA has since tightened the intake valve deposit limit, but they have yet to set limits for injector deposits in gasoline direct injection engines, even though four out of every five of new U.S.-market cars and trucks now use GDI.
In the early 2000s, several automakers decided the EPA standards were not strict enough to adequately protect their newer engines and established their own voluntary deposit control performance standards, administered through a licensing program called TOP TIER. The TOP TIER standards meet EPA and CARB requirements, but also have some additional performance standards, including ones limiting combustion chamber deposits. TOP TIER distributors have to meet these standards for all octane grades their stations sell, not just premium fuels, but the TOP TIER rules do allow retailers to specify higher additive concentrations for higher octane grades, at up to three times the approved minimum rate.
Is More Detergent Better?
Auto enthusiasts have a tendency to assume that if a little of something is good, more must be even better. The companies that sell fuel additives have enthusiastically exploited that knee-jerk assumption for years, but it’s not necessarily true when it comes to fuel detergent and deposit control additives.
Over the years, there’s been ample evidence that excessive detergent concentration can cause unintended harm. For example, in 1970, a Chevron study found that high concentrations of certain detergents caused serious damage to piston rings — some tests had to be stopped because of stuck rings or plugged oil control rings. In 2021, a GM study found that very high detergent concentrations — well above the allowable TOP TIER limits — significantly increased the risk of stochastic preignition (also known as low speed preignition) in turbocharged gasoline direct injection engines, which can cause severe engine damage. (Some researchers have disputed those findings, but it’s obviously a matter of concern, and the latest TOP TIER+ standards now incorporate additional GDI “no-harm” requirements.)
Even the TOP TIER Program FAQ emphasizes, “Merely adding more detergent doesn’t necessarily mean a fuel is better.” Different detergents may need different concentrations to achieve the same results: For example, the GM study reported that one common additive, polyether amine (PEA), needed a concentration of 85 pounds per 1,000 barrels to meet the TOP TIER standards, but another, polyisobutylene amine (PIBA), needed only 58 pounds per 1,000 barrels. What’s most important is not the detergent concentration, but how well the additives actually perform.
The chemistry of these additives and the deposits they’re supposed to control is complex (and is still not as well understood as you’d expect). However, a useful analogy might be liquid hand soap: Using soap and water to wash your hands is much better than water alone, but using three or four times as much soap won’t get your hands three or four times cleaner, and it might plug up the drain.
Ironically, modern engines are still susceptible to the kind of throttle plate deposits detergent gasolines were originally developed to clean up. Even with port or direct fuel injection, dirt will tend to build up around the edges of the throttle plate at idle speed. Modern engine computers will compensate for the flow restriction (at least to a point), but since the throttle body and manifold are “dry” (with fuel added at the intake port or directly injected into the combustion chambers), detergent gasolines and fuel system additives can no longer do anything to clean it up.
Related Reading
2016 AAA Fuel Quality Research Report on Fuel Additive Effectiveness
Current EPA Fuel Additive Regulations (at 40 CFR Part 1090)
California Air Resources Board Gasoline Deposit Control Additive Rules
TOP TIER Performance Standards for Gasoline and Diesel Fuels
1954 Texaco Sales Film on PETROX Additive
Whenever I hear the term “detergent gasoline” I immediately think back to this Mobil TV commercial from the 1970’s.
This was interesting. I routinely pump Top Tier gasoline into my cars (at Costco) but have always wondered what makes it “Top Tier”. Now I know!
This was a pleasure to read this morning—thanks very much. Nice research, clean-and-clear writing, and really useful illustrations.
All these decades, I’ve carried around only vaguest notion of what “detergents” and “additives” do, and I now know a lot more than I did a dozen minutes ago.
Who would benefit the most from promo-explaining what makes “Top Tier” gasolines better than merely minimum—the producers, or the retailers? Whoever it is, I’d think it in their best interest to do so.
Bravo, Aaron Severson…..a really fine writeup!
Thanks for the history here. Detergent gasoline isn’t something I thought about much until we bought a GDI-equipped Kia in 2018, and Top Tier gas was recommended. I hadn’t even heard of Top Tier prior to that, but afterwards (and seeing how many cars now have GDI engines), I wondered why Top Tier standards weren’t universal.
From what I understand, since Top Tier is a licensing program – and presumably retailers and/or refiners need to pay to get their gas certified – some companies will just skip that step, figuring that few people actually check. That happened recently (as far as I know) with BP, whose gas used to be Top Tier certified, but now it isn’t. I suspect the gas is the same, but BP just doesn’t want to pay the licensing fees. That’s frustrating for those of us who actively seek Top Tier.
In addition to using Top Tier gas, I use Tekron every few thousand miles. Kia’s owner’s manual specifies some sort of Kia-brand fuel cleaner, but I suspect that’s just rebranded Tekron.
Anyway, thanks for the background story.
I filled up at a BP station last week, and it now has a Top Tier sticker on the pump. Before it just said “Invigorate.”
Interesting. I just checked the Top Tier website (where they list their licensed brands), and BP’s still not on the list. Frustrating when you get mixed signals.
I use Exxon or BP exclusively, mostly BP because that’s most convenient. BP definitely used to be listed as Top Tier which is why I chose it. I e-mailed Top Tier because the Exxon station didn’t show the Top Tier sticker and they assured me that it was part of the program and not all stations displayed the sticker.
Now I’ll have to write them about BP. I also got on the bandwagon because of a Kia with a GDI engine although now I drive a Subaru. If BP no longer qualifies, I may as well go to the Murphy (not T-T) station nearby for the lower prices.
Thank you for your email about British Petroleum (BP/Amoco). At this time, we ask that you stay tuned for an upcoming program announcement…
The TOP TIER™ Team
The program is for retailers, not refiners. (Even with non-TOP TIER fuel, additives are generally the distributor’s responsibility, since different markets may require different additive packages.) There is a licensing fee for participating, and conformance to the standards has to be tested by a third-party independent laboratory, rather than in-house.
The TOP TIER Commercial FAQs address a lot of the general questions, although they don’t specify exactly how much it costs: https://www.toptiergas.com/commercial-faqs/
But I’m left wondering if it’s better to use only one brand and grade of gas or does switching brands and grade improve my chances to reduce deposits in my engine
It depends: If you’ve been using a cheap low-quality gasoline and then switch to a TOP TIER gasoline, it will likely do a better job of reducing intake valve and injector deposits. If you mean switching between different TOP TIER brands, no, likely not.
Nice detailed article .
FWIW, two stroke Diesel engines were indeed cleaned of excess carbon by putting an Oxy-Acetylene torch in one port and once the carbon got really hot you’d turn up the oxygen and the carbon would blow out dramatically in sparks….
Older Mechanics like me will remember carefully scraping carbon out of combustion chambers and piston crowns, care had to be taken to not leave any scratches / grooves that would of course collect more carbon rapidly .
The 1970’s Mobil TV commercials I remember had some filthy old guy riding under the hood just waiting to gunk up your engine .
-Nate
I must be being dumb, but in the top photos how does detergent in the gasoline keep the valve gear clean?
This is actually not super-obvious, so don’t feel bad! The answer is that the separation between the intake/fuel system and the valve system and bottom end is not nearly as rigid as we tend to think. Even a healthy engine produces a substantial amount of blowby, which is combustion byproducts forced past the rings into the crankshaft, and blowby increases with wear. The Lubrizol Corporation, whose study that’s from, explained that the additives “”provide a continuous new increment of dispersancy to the crankcase. This added reserve of dispersant, when needed, assures cleaner PCV vales as well as better overall engine cleanliness.”
In English, that means that the detergent additives also tend to make the oil less dirty.
without being a Phd in chemistry and physics (airflow) I and most if not all of us must rely on the marketers.
This has been a love of mine in that I have learned that with top tier gasolines there is a difference. As of now my understanding is that AMOCO products are best. That is subject to change in the future but for now I use their products. Also if you use additives again Techron is the standard.Someone before me said he uses it every 3000 miles tankfuls. His Kia should run great .
See above comments. Amoco and BP are the same company and neither are listed on the Top Tier website.
https://www.toptiergas.com/gasoline-brands/
I was certain that they were Top Tier and used almost always bought BP gasoline. I think they have recently left the fold. I have sent an email asking for confirmation on the matter.
Thank you for your email about British Petroleum (BP/Amoco). At this time, we ask that you stay tuned for an upcoming program announcement…
The TOP TIER™ Team
Great read as always, Aaron. I use top tier fuels exclusively, namely Chevron 94 octane. Yes, it costs more, but my car calls for premium, so I don’t have the choice to use regular. I have used Chevron 94 in all my vehicles over the years and I have yet to have a problem with combustion/intake valve deposits.
Thanks for this Aaron. While I knew about Top Tier for a while now, it was still nice to see it explained. While I don’t use it exclusively due to various circumstances, I do seek it out, most of the time.
Like many others, I’m a fan of the Chevron Techron for the fleet, but don’t do that every 3,000 miles. The article implies “too much of a good thing” being done by enthusiasts with its “more must be even better” comment. For our cars, it’s about every 12,000 to 15,000 miles. The Mustang may get it more often than this, because when the two direct injected Japanese cars get the Techron added to a tank, I usually do the Mustang at the same time, and put considerably less miles on that car than the other two.
Hopefully, this is sufficient. I haven’t had any fuel deposit issues, or any damage from doing it too often, either.
I would be remiss if I didn’t reference my (childhood and now) best friend’s uncle – the actor/comedian/writer Ronny Graham – also known as Mobil’s Mr. Dirt.
While quite entertaining, I’m have to say that Uncle Ronny probably didn’t do the world of automotive science any favors by leaving millions of television viewers with the idea that the kind of dirt that Mobil prevented was basically something akin to potting soil. I remember wondering as a little kid just how all of that soil would get into your car’s engine (if not for the various mechanisms involving Uncle Dirt – as my mom always called him as in “JEFF!Come look! Jim’s Uncle Dirt is on the television!” – dumping or pumping it into the engine as seen in commercials).
Excellent, informative post. Thank you, Aaron.
It reminds me of problem solving my rough running 2002 4.7L Dodge Next Gen V8. Ultimately I removed the throttle body and I think the intake manifold. I was flabbergasted by the carbon buildup and wondered about the detergent additives thinking it was marketing BS.
I thoroughly cleaned it only to realize I should’ve removed the TPS…
With port injection and/or GDI, there’s no fuel in the throttle body or the manifold. So, no amount of detergent in the fuel is going to reduce that buildup.
Thank you Aaron, a very informative read!
Gasoline ‘detergents’ do nothing to keep intake valves clean on GDI engines. Fuel is injected downstream of the intake valves (directly into the cylinder). This means that any PCV or EGR system will deposit an oily film on intake valve stems. Some engine manufacturers have included additional port injectors which do help keep intake valves clean.
Fuel additives have significantly *less* effect on intake valve deposits in GDI engine due to lack of fuel wash; “do nothing” is an overstatement.
Thank you for this very informative article Aaron. My newer Toyotas have recommended (but not required) Top Tier fuels and I have long wondered if there was any real basis for such fuels being any better than those not so labeled. The licensing stipulation is interesting as there may very well be gasolines that meet the requirements but have not paid for licensing.
Since I joined the Costco brigade a couple of years ago, I do try to fill up there at least every other time. and on trips stick to the major brands like Exxon, Sunoco, Shell and so on. Interesting about BP, which apparently stopped paying the license fee.
Another fantastic article. This is the reason I come back daily. Thanks Aaron!
The local grocery store chain gives coupons for a local gas-station chain. Depending on how much you spend on groceries, you receive a 6-cent, 10-cent…all the way up to 25 cent per gallon discount coupon. Two coupons can be used at a time, so theoretically a 50-cent-per-gallon (12-gallon limit.)
This was wonderful when those stations were peddling Top Tier fuel. In fact, they advertised “More” detergent than required by Top Tier. Then, that small regional chain of gas stations got bought-out by a national chain. Now, only “Premium” is said to have “extra” detergent beyond legal minimums; the Top Tier branding is gone, and there’s no more pump-then-pay, we are forced to pre-pay as if the whole world was nothing but drive-away criminals.
I’ve been using Techron Complete Fuel System Cleaner–a 20-oz bottle in the gas tank at every oil change. GM used to sell a GM-branded fuel system cleaner; (Might have been “X66P”) the bottle shape was exactly the same as Techron, and if you flipped the bottle upside-down, you could see the “CHEVRON” brand name molded into the bottle.
NOW GM is selling “44K” which I think is a BG product, not Chevron.