Car Advice

Dirt-Busting Fuel… fact or fiction?

20 Nov 2018

Isaac Bober 13

Most fuel companies in Australia claim their high-octane fuel contains dirt-busting properties… but what does that mean?

NOTE: This article was first published in 2017 but with a particular fuel company paying a lot to promote its dirt-busting fuel as ‘editorial’ on automotive websites I thought it would be worth reminding people that all fuels (petrol and diesel) have to contain cleaning agents.

DIRT-BUSTING FUEL. Do a quick search of the internet and you’ll realise just how clever the marketing department of one fuel company, in particular, has been, and how totally lacking in quality control most news outlets are.

Now, I wouldn’t quite go as far as Donald Trump, and call Fake News on this stuff, but I would say that when a handful of reasonably well respected publications, from The Telegraph in the UK, to auto industry publication, GoAuto (here in Australia) and many others suggest that BP’s dirt-busting fuel is a unique, wunder-fuel then people are likely to dig into their wallets to keep their engines running clean.

And I’m not saying they shouldn’t, because the fuel really does have dirt-busting properties, as do all of the others claiming so, and even some that don’t, too. I’m just calling for a breath to be drawn and some perspective applied to the situation.

BP isn’t alone in peddling its dirt-busting fuel. Surely you’ve all seen the TV Ads with a gunk monster following a car down the road, only to be blown to smithereens when the hero fills his car with expensive “dirt-busting” fuel. Or the pink anchor dragging behind another car, via another fuel company trying to illustrate the effect dirty fuel has on your car.

When it announced the release of its new dirt-busting high-octane fuel, BP said: “Ordinary fuels have been shown to result in the formation of harmful engine deposits that can clog up critical engine components, reducing fuel economy and engine performance. BP Ultimate has been specially designed to fight the negative impact of deposits on key engine components. (And this is true -Ed)

“The formulations of the new BP Ultimate fuels contain special molecules that attach themselves to dirt, releasing it from key engine components. The fuel is then burned in the combustion chamber”. Only that’s not true (the molecule bit)… it’s a cleaning agent, otherwise known as detergent, but that doesn’t sound quite as cool. We’ll get into this as we go on…

What started out as an article on the dirt-busting properties in some fuel retailers products has grown into so much more. To be honest, I’ve raised more questions than I’ve answered, but the one key stand-out is that Australia needs to pull its finger out to improve the quality of fuel available in this country, and ensure our fuel retailers are more transparent on just what additives, and the levels, are in their fuel.

So, what is this dirt that needs busting?

All fuel contains ‘dirt’ (sediment) and suplhur, and it’s this stuff (depending on the amount in the fuel) that can cause a build-up of gunk on intake valves in petrol engines causing the engine to have to work harder, or inside a diesel engine’s fuel injectors and on the injector tip causing an irregular spray of diesel and thus affecting combustion. Excess sulphur in fuel can also cause a breakdown of fuel tank sensors, and is a major contributor to tail-pipe emissions.

All vehicles have fuel filters which are designed to filter out the larger bits of rubbish that run down your fuel line, but they can’t always catch the super fine stuff (like sulphur) that causes a build-up of gunk on key components of your car’s engine. If they could, then we wouldn’t need any cleaning agents added to fuel in the first place.

According to the latest edition of the World Fuel Charter (5^th edition), which most automotive bodies are signatories of, unleaded fuel should contain no trace metal elements, only 1mg/L of sediment, no more than 30g/kg of Sulphur and that there should be added fuel injector cleaners, intake valve cleaners and combustion chamber cleaners; this is the dirt-busting additive BP and others are referencing to in their marketing.

So, if all fuels (petrol and diesel) must contain cleaning agents anyway then what’s BP talking about? Simple, it’s referring to the fact that its BP Ultimate Active 98RON fuel contains a higher amount of cleaning agent than its other fuels. It’s a little bit of marketing smoke and mirrors, although it doesn’t say how much more than normal.

So, it’s not only the expensive fuel that gets a cleaning agent?

No. BP has told Practical Motoring it won’t roll-out its dirt-busting additive across its fuel range but what it’s saying is that it won’t lift the amount of cleaning agent in its other fuels to match its Headline-Grabbing stuff. Although, we don’t actually know just how much extra cleaning agent it adds to the top-shelf fuel. Or, maybe it doesn’t actually have a cleaning agent in its other fuels… some fuel retailers in Australia have cleaning agents in all their fuel.

Indeed, the Mobil Australia website says exactly that: “A detergent additive is present in Mobil petrol grades Special Unleaded 91, Special E10 94, Extra 95 and Supreme+ 98 and in Mobil Diesel grade Special Diesel […] the additive is designed to improve engine performance by helping vehicle engines run more smoothly. It works to help remove harmful deposits from vital engine parts (fuel injectors and intake valves) that can build up over time”.

And, Caltex too admits that its fuels contain a cleaning agent, but that its premium fuels contain around 25% more of the stuff. New player, in the service station market, Costco, says its Kirkland Signature Range of fuel contains deposit control additives, but doesn’t detail the level.

So, it stands to reason that the higher-octane fuels with deposit control additive will be more effective than a cheaper grade of fuel (with potentially no cleaning agent added) at keeping the engine clean. But, what hasn’t been answered, is whether the additive concentration in these more expensive fuels would be more effective than simply adding an off-the-shelf fuel cleaner when you fill up.

Does the dirt really compromise performance?

Yes, it does, but it’s unlikely you’ll be able to tell the difference. In a recent study by the AAA in the US (it’s an organisation along the same lines as the Automobile Association of Australia), it was revealed that gunk build-up in an engine (specifically on the intake valves; the test was petrol engine only) can reduce fuel consumption by 2-4% but that performance drop wouldn’t be noticeable to the driver.

The AAA also found that filling up using low-detergency fuel caused a build-up of gunk of 660mg per intake valve as opposed to 34mg per intake valve on high-detergent fuel, but it didn’t state the specific levels of detergent in the fuel…

But, of most interest in the AAA testing was its finding that while engine performance was negligible on one or the other type of fuel, it found that carbon-monoxide emissions were reduced when running a Top Tier fuel, that is a fuel with two- or three-times the cleaning agent as mandated by the EPA in the US.

“Testing has shown that running an engine on a non-enhanced additive package fuel can roughly double carbon monoxide emissions (180-200% rise) and cause a 20-30% increase in hydrocarbon emissions. These emission increases were measured ahead of the catalyst over the course of 55 hours of dynamometer testing that equated to approximately 2000 miles (3200km) of real-world driving. The engine was then switched to a fuel with an enhanced additive package and the emissions returned to normal levels after about 1,000 miles of real-world driving as simulated on a dynamometer,” the AAA said.

It’s worth nothing that most research has been conducted on the performance of cleaning agents in petrol, but the cleaning agents in diesel are a very similar compound and will benefit all diesel engine types, be they older or a modern unit. Diesel cleaning agent consists of a compound to scour away the deposit and a compound that coats the surface of the metal (making it slippery) to help reduce further build-up. In the early days of deposit control additives for diesel, the cleaning agent was too strong and actually stripped the essential lubricating nature of diesel, and so adjustments to the formulation were needed.

According to Hungarian researchers writing on the Development of Deposit Control Additives for Diesel Fuel in 2009, “DCAs (deposit control additives) [in diesel fuel] are generally long chain hydrocarbons attached to a polar head group. Deposit precursors are attracted to the deposit control molecule, and become bounded into the dispersant micelles. At normal operating temperatures the DCA is a liquid that forms a thin film on the surface of the inlet system. The thin film is driven forward by air and fuel vapour flow, but forms a first line barrier to deposit precursors as well as a dispersant/neutraliser of the precursors protecting the metal surface. In the case of deposits on the metal surface, the liquid film slowly removes them by a detergent action”. This is the same principle as cleaning agents in petrol but they now don’t strip away the engine lubrication.

How much cleaning agent is in fuel?

That’s a hard question to answer, especially where Australia is concerned as none of the fuel companies will publish just how much detergent is added to their fuel. Overseas, however, there have been a couple of studies that found regular unleaded can contain between 6-20milligrams/100mL of deposit control additive. In high-octane fuels the cleaning agent levels can be as much as 31mg/100mL.

Are cleaning agent levels comparable to other fuel additives?

No. Deposit Control additives (cleaning agents) are used at concentrations that are 20 times to 50 times higher than the concentrations of other petrol additives. Because of the high concentration of these agent in fuel there’s a good chance they can affect other parts of the fuel system, and so deposit control additives are tested for the absence of negative attributes (no harm) as well as for the positive attribute of controlling deposits. Fuel containing cleaning agents must be “fully compatible with the elastomers and metals it will contact. In addition, it must be compatible with other gasoline additives, tolerate water well, and not contribute to spark plug fouling, crankcase sludge formation, or intake or exhaust valve sticking,” according to the EPA.

How is the cleaning agent dispensed into fuel?

Usually detergent is added to a base load of fuel when it’s loaded into a tanker which usually holds around 30,000 litres. It’s dispensed electronically via an applicator in the tanker itself, pumping in up to 20 litres, or more, of detergent. Depending on the fuel company, the amount of cleaning agent will vary, but the base chemical will likely be the same, and these are: polyether amines and polyisobutylene-based (PIB) compounds such as (PIB)-Mannichs, (PIB)-amines, and (PIB)-succinimide. 

What’s the go overseas?

In the US, after car makers got together and complained that the poor quality of fuel sold in that country was causing repair issues the Environmental Protection Agency stepped in (1995) and mandated a certain amount of cleaning agent must be included in all fuel sold in the US. But that didn’t stop issues, like intake valves becoming gunked up or fuel tank sensors to be eroded by the amount of Sulphur in the fuel.

So, at the behest of the car makers, US fuel retailers formed the Top Tier Program which saw the amount of cleaning agent included in both petrol and diesel increased by two- to three-times the amount mandated by the EPA.

Most car makers have come out and publically promoted the use of Top Tier fuels to their customers, with some claiming they’ve seen a reduction in repairs related to intake valves and fuel injectors becoming gunked up. According to the GM’s head of fuels, Bill Studzinski a dirty engine would be imperceptible to the driver, saying GM is a supporter of detergent in fuels because “we’ll often get a rash of warranty issues related to low-detergency” causing fuel sensors to fail.

Honda America PR executive, Chris Martin has been quoted widely as saying, “We’ve supported it [Top Tier fuel] because we’ve seen a benefit from it for our consumers in the long run […] We don’t require that our vehicle owners use Top Tier gas [fuel] [but it helps] make sure the engines are going to last as they could”.

All Top Tier fuels must be performance tested by an independent ISO 17025 (which covers the competence of testing and calibration labs) accredited laboratory. In March last year, Top Tier revised its Deposit Control Performance Standard to include a more stringent test of the performance of the cleaning agents, and that Top Tier fuels aren’t just high-octane fuels, but all the fuels in a fuel retailers armoury, meaning the cleaning power is the same no matter the octane rating.

Do car companies agree that fuel should contain a ‘certain level’ of cleaning agent?

Yes. BMW, Toyota, Audi, FCA, GM, Honda, Volkswagen and Mercedes-Benz are all on record as saying the minimum detergent requirements in many countries don’t go far enough to ensure engine performance. All have stated in the US editions of their owner handbooks that Top Tier fuels should be used in their vehicles.

In Australia, there is no minimum requirement for a ‘level’ of cleaning agent, because according to the Proposed Standards for the Fuel Parameters (Petrol and Diesel) 2000, cleaning agents and general additives are already added at the refining stage (in other countries its added at the fuel delivery stage), and that there are a number of off-the-shelf products available. But that document doesn’t specify how much cleaning agent is added at the refining stage or whether it adheres to the World Fuel Charter recommendations. Given the importance placed on this topic in other countries, it seems odd that motoring groups and car makers here haven’t jumped on the bandwagon…

Practical Motoring sent a list of questions to BP’s Fuels Marketing boss, Ryan Wade, and here’s what he said (and, no, this isn’t a paid for post in any way shape or form as I’m sure you’ve already gathered):

Practical Motoring: How did BP determine that fuel was inherently dirty and that the ‘dirt’ wasn’t already being filtered out by the fuel filters in a car?

BP: The first thing is to get the right concept of ‘dirt’.  Dirt is the cumulative product of fuel oxidation from ageing and exposure to heat and oxygen.  ‘Dirt’ is essentially carbon and oxygen based gums and soot left over from the fuel burning process.  In the same way that a barbecue will start out clean but after being used it will accumulate a carbonaceous dirt or gunk, a vehicle engine exposes carbon based fuel to air and high temperatures resulting in dirt or gunk deposits accumulating in the engine. This has always been an issue with combustion engines and in the past was dealt with by regularly decoking the engines. Engines are now more technically sophisticated with much longer service intervals such that, the process of removing the dirt or gunk needs to be continuous to get the best performance out of an engine.

Practical Motoring: How did BP study the dirt in fuel, and did it look at fuel quality across the world or just in the UK where Ultimate with its dirt-busting additive was developed?

BP: BP has long studied the impact of dirt in engines with the aim of providing a better quality of fuel to the consumer. It impacts all types of engines from heavy mining, transport all the way down to passenger vehicles. Part of the Ultimate development process involved looking at fuel quality across the world and testing the formulation in fuels from different parts of the world to ensure that it provides the claimed benefits in every market e.g. busts dirt in just two tanks. For example, fuel from Australia and New Zealand were sent to the BP testing centres overseas to allow for claims testing with local fuels. BP doesn’t say how much cleaning agent is in its BP Ultimate Active fuel.

Practical Motoring: How can a punter tell if there is dirt building up in their engine?

BP: Dirt can lead to a loss of performance, rough running and reduced fuel economy. The average punter cannot always tell if there is dirt building up within the engines because it is a slow build up process. They may feel that performance and power are not what they used to be. Their vehicle’s engine could struggle when climbing a hill and has to change down gear more often, typically a symptom of reduced power, or the engine may struggle or seem stressed on hot days. When using BP Ultimate after a prolonged spell on ordinary fuels punters generally see an improvement in performance, the vehicle accelerates better, the engine runs better without the hesitation or lumpiness caused by dirt accumulating in the engine.

This statement needs to be taken with a grain of salt as there are a number of reasons for a loss of performance but, generally speaking, yes, a dirty engine will cause reduced performance. But not in quite the way BP suggests, according to testing by the AAA the performance effects of a dirty engine would be barely perceptible by the driver and would most likely effect things like knocking or pinging caused by pre-ignition, but because most cars have knock sensors that their engine control systems use to retard the ignition timing and/or add additional fuel to prevent detonation and, to a lesser degree, pre-ignition. Dirt build-up will likely be most noticeable via a rough idle, with the biggest impact on fuel consumption because the engine is having to work harder.

Practical Motoring: By saying that BP Ultimate will bust the dirt in a car’s engine and that regular fuel is dirty, is BP admitting that its own regular fuel is dirty?

BP: All hydrocarbon fuels burn dirty in engines because the combustion process is not perfect (it has to allow for many different speeds and operating conditions). In the presence of air and heat all hydrocarbon fuels will form gums and dirt which is a natural oxidation process.  BP is not saying that it’s fuel is dirty, we are saying that regular fuels without the cleaning properties and formulation of Ultimate can potentially clog your engine with dirt after prolonged use.

Practical Motoring: Thus, will BP consider rolling out its dirt-busting additive to its regular fuel lines?

BP: Not at this stage.

That final statement, if I can editorialise at the moment, sounds pretty darn cheeky. By refusing to include a deposit control additive in its regular line of fuel, it’s, more or less, forcing motorists into spending more on fuel that’s better for their car’s engine, putting aside whether their car has even been tuned to run on 98RON fuel.

What about off-the-shelf additives?

There are also off-the-shelf products you can buy to add to your fuel system that will help clean the ‘gunk’ from fuel injectors and intake valves. Following the manufacturer’s instructions should see these products cause no damage to your fuel system and engine, but whether they’ll make a noticeable difference in a once-off application is another thing. And you wouldn’t want to make up your own cocktail and tip half-a-dozen bottles of the stuff into a tank of fuel as that will seriously compromise the chemical structure of your petrol and likely to do more harm than good.

While the motoring club, RACV admits these products do work, just how well they work will depend entirely on the magnitude of the problem; with more drastic intervention required (replacement of the fuel injectors or intake valves) if the issue is serious enough.

What would be of more use, is if we knew the current level of deposit control agents in Australian fuel. This would allow motorists to determine whether its cheaper to buy a bottle of cleaner as opposed to filling up with a high-octane ‘dirt-busting’ fuel.

Should I bother filling up with higher-octane fuel with a higher concentration of cleaning agent?

Well, at the end of the day, that’s a decision that only you can make. Spending more money on fuel with more cleaning agent than Regular Unleaded (95RON) certainly won’t hurt your engine. But, while fuel companies selling this dirt-busting fuel in other markets, must have their claims tested by an independent laboratory running a standardized series of tests, there’s no such requirement in Australia. And, while we asked BP for its data, it said it only released its test results and the make-up of its fuel if required by a Court.

So, in summary, all fuel sold in Australia contains an amount of cleaning agent, but some allegedly carry more than others (none of the fuel retailers here have submitted their fuel to independent testing) – there’s no mandated amount of detergent that fuel sold here should contain. And there’s the rub; other countries have mandated an amount of cleaning agent that should be in fuel, but not Australia.

Maybe we should be pushing for improvements in fuel quality in Australia (like the introduction of cleaning agents in higher concentrations, reduction in the sulphur content and a reduction in aromatics), and that fuel companies should be pushed to submit their products to independent testing.

And, while we’ve seen this argument derail online and end up being about octane ratings, remember that the presence of a cleaning agent in fuel (petrol and diesel) is a different story to whether you should spend more money on higher-octane fuel for your car.

Question: Should Australia’s fuel retailers be required to have a certain level of ‘cleaning agent’ in all their fuels, and should those claiming enhanced dirt-busting properties, have their fuel tested by independent labs to assess the cleaning effectiveness of the detergent?