Car Advice

Dirt-Busting Fuel… fact or fiction?

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

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 (5th 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.

 

 

Do dirt-busting fuels work?
Image courtesy of the AAA. Top Tier Gasoline is petrol that contains a higher concentration of cleaning agent (deposit control).

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. 

According to the Book of Detergents, “Polyether amines are effective at controlling combustion chamber deposits, but less effective with intake valve and fuel injector deposits. Both PIB-amines and PIB-Mannichs are effective at controlling intake valve deposits and slightly less effective at preventing fuel injector deposits. PIB-succinimides are moderately effective against port fuel injector deposits, but relatively ineffective at controlling intake valve deposits”.

The first generation of fuel cleaning agents

The first lot of deposit control additives were known as carburettor cleaners which were introduced in the 1950s, but proved less effective in controlling deposits as engine technology changed into the 1960s and ’70s, because of the introduction of positive crankcase ventilation (PCV) and exhaust gas recirculation (EGR) emission control systems which actually increased the level of deposits in engines.

From 1968 detergent dispersants began being used in fuel at levels three- or five-times higher than the original carburettor cleaning additives. This additive continued to be effective until the introduction and wide take-up of unleaded fuel; this saw the introduction of the first-generation of what were specifically known as deposit control additives in 1970.

However, with the arrival in the 1980s of electronic fuel injection systems car makers began experiencing issues with injectors sticking or becoming clogged due to contamination in the base fuel. These port-fuel injected engines sprayed fuel directly above the intake valves, which resulted in carbon build-up on the injector nozzle and backside of the intake valve. Some of these engines were susceptible to fuel varnishing near the injector tip, caused by fuel trapped inside the injector, when the car is switched off, being subjected to intense heat and thus causing ‘deposit formation’. 

Fuel companies responded by pumping petrol full of aggressive detergents, and that helped clean up the intake valve, but it caused combustion chamber deposits, otherwise known as ‘coking’. If the build-up got too bad it could cause engine failure due to the interference in the performance of the pistons, valves and cylinder heads.

The second-generation of detergents was developed which eliminated both issues. This is the generation of cleaning agent we have now.

How do cleaning agents in fuel work?

According to the Handbook of Detergents, “Each detergent type shares a common general structure; consisting of a long hydrophobic tail comprised of a varying number of monomers, and a hydrophilic nitrogen-containing head. The purpose of the hydrophobic region of the compound is to increase solubility in a carrier fluid. The nitrogen- containing head varies depending on the specific nitrogen-containing functional group. Common functional groups are amines, Mannich (aromatic amine), and succinimides.

“It is generally believed that the hydrophilic nitrogen-containing region of the detergent is responsible for preventing deposit formation by adhering to the metal surface and forming a thin hydrocarbon film. It is also believed that, at higher concentrations, detergents can remove deposits by dissolving the soluble part of the deposit, which binds to the surface of the metal.”

What’s the go with the fuel quality and cleaning agents in Australia?

Good question. While Australia’s fuel (both petrol and diesel) generally line-up with guidelines set in places like the US, EU, Japan and South Korea, Australia is way out of step when it comes to the amount of sulphur in our fuel. Currently, Australian petrol contains between 150 parts per million of sulphur in regular unleaded fuel and around 50ppm in premium unleaded. However, the EU, Japan, South Korea and the US (just this year) have all had a sulphur content level of 10ppm, with some countries mandating this level in 2003 (Germany).

It is widely believed that a reduction in the sulphur content in fuel can contribute to a reduction in tailpipe emissions. And the same goes for aromatics which, as the name suggests, give fuel a sweetish smell. They also help to raise the octane rating of fuel… In most countries, there is an aromatics restriction of 35vol%max, indeed, the EU introduced this in 2006. However, here in Australia the aromatic content of our fuel is up to 45vol%max. Aromatics are a further contributor to tailpipe emissions.

The above were the key recommendations in a paper submitted to the Australian Government in 2014 by Hart Energy. The Government has not adopted the recommendations, which Hart Energy claimed could have a dire effect on the ability of car makers to sell their latest vehicles in Australia, because of the high sulphur content in our fuel and its incompatibility with new-generation fuel-efficient and emissions-reduced engines.

So, what about cleaning agents in Australian fuel? Nowhere do they rate a mention. If you do decide to trawl the Net for information on cleaning agents in fuel, then you’ll be looking for references to additized fuel and deposit control agents.

Other recent studies, like the Review of Sulphur Limits in Petrol, published in 2013 have looked at the impact of keeping the sulphur content in Australian fuel where they are and all have concluded that there will be an increase in tailpipe emissions, but all have fallen short of suggesting the sulphur content should be reduced, rather that car makers should work harder on emissions control technologies to work with the high sulphur content in Australian fuel.

There is currently a draft submission to Government that’s proposing the removal of regular unleaded from sale across the country, with many claiming it would be an instant air quality win for Australia. And it would, but would make more sense is if Australia simply adopted the 10ppm sulphur content in all fuel (regular and premium) that’s been mandated in many countries across the world.

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:

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?


  • JohnGC

    Isaac, I like how you ask yourself a question and then in your reply tell yourself it was a good question. A bit of positive self talk.
    Your article actually convinced me to stick with Ultimate. I was using it all the time, my leasing company gives me a discount for BP and the servo is close to home, but recently started using the ethanol mix 94 that BP has. But as I understand it, the Ultimate is better for my car and has reduced emissions compared to fuels with less detergent. But environmentally, the ethanol blend is still probably a better choice, but it won’t have the detergent benefits that Ultimate has. Have I understood that correctly?

    • Hi JohnGC, that is a good question 😉
      Here in Australia it’s a tough one to answer definitively… But, yes, on the surface, you’re better off using a fuel that does contain deposit control additives… better for the environment (as a dirty engine is more polluting) and better for fuel economy. But, Mobil offers deposit control additives across all of its fuel in Australia and not just one or two, like BP.
      I hope this helps? – Isaac

      • JohnGC

        Yes, thanks that does help. I’m probably operating out of fear a bit too and the marketing people know how to push consumer buttons. Spend $40K on a car and you don’t want to wreck it with inferior fuel (as the ads allude to) just save a few dollars. But compared to the ethanol mix the price of Ultimate has been as much as 23 cent per litre more ($11-$12 in my car!).

  • Glenn59

    I think the benefits of these additives in fuel is questionable. More and more cars now are direct injection and the fuel no longer cleans the valves as it enters the combustion chamber. Premium fuel is very expensive and a large number of motorists are using it unnecessarily. These additives are mostly marketing tools rather than actually doing very much for your car in my opinion.

    • Hi Glenn, a study in the US showed that they do help keep key parts of the engine cleaner than if you don’t use them. What frustrates me is the lack of ‘evidence’ to support the claim that it’ll work in two tanks. We’re continuing our conversation with BP. – Isaac

  • Monty

    I’m using 98 in my car, the recommendation is minimum 95. A mobile mechanic I used for years (he does not service my current vehicle type) uses 98 in his Toyota van. Various forums advise that 98 is good for my car. It’s usually 10 cents a litre more than 95. I generally put 50 litres in each time. That’s about a take away coffee difference. It would be wonderful if consumers actually knew what they were getting. You can find out exactly what is in your cornflakes but not in petrol. Surely the fact that you are paying for a product gives you some rights to know the contents?

  • Johnny Manbeard

    This is certainly the most comprehensive article I’ve come across on this subject. Thanks for the depth and detail.
    I can only add my own subjective impression which is that 98 octane premium fuel seems to give better performance and economy over the 95 RON in my 2013 SSS Nissan Pulsar.
    This article suggests that my emissions are probably lower as well, so I will continue to but the higher priced fuel.
    My question is about the comparison of petrol to diesel. Many diesel owners refer to the better fuel economy from their oilers. My impression is that this doesn’t nearly make up for the increase in noxious emissions produced by a diesel. Do you think that a petrol engine, despite its increased fuel consumption, is better than a diesel on environmental grounds?

    • Generally yes which is why the tide is turning against diesels, but it depends on many factors – how modern the engine design is, and the load on the engine. Best of all is a hybrid.

  • bmcdude

    This is all sort of pointless in the age of direct injected engines i.e. fuel is injected into the combustion chamber rather than the throttle body or inlet manifold close to the valves.

    The fuel never comes in contact with the valves in a direct injected engine, so the valves are not being cleaned by the fuel regardless of additives.

    The above is a problem for modern engines, particularly diesels, as the EGR (emissions) systems plum (hopefully) small amounts of oil vapour from the crankcase of the engine through the inlet manifold, with no fuel going through the manifold and past the inlet valves these oil deposits stick and start to clog things up reducing efficiency over time.

    In older non direct injected engines normal 91 is generally plenty “cleansing” enough to get EGR related oil deposits of inlet valves.

    As for the 91 vs 95 vs 98, your milage may vary (literally) but generally if your (non performance) car only needs 91 (i.e. just about any toyota) doesn’t ping and you are using 95/98 you are likely pissing away money on more expensive fuel for a (very) nebulous gain in economy or performance vs cost.

  • Luke Nguyen

    I load the stuff in a tanker. All BP petrol going to licenced resellers has additives,I watch it metered in when I load, only ultimate diesel gets it. What additive it is I don’t know. Independents get no additive. An example is 7-11, before they used the Mobil branding they got base product. 7-11 were using Mobil for quite a while before this. For what it’s worth I wouldn’t trust United Petroleum product as far as I could kick it.

  • Hilldene

    I took a Rav4 for service and they told me that fuel in Australia is now cleaner so Toyota had doubled the life of the fuel filter.
    I have used three 98 octane fuels and they give better performance.
    Fuel 1. A 1600cc manual car had a generous increase in acceleration.
    Fuel 2. Same car drove smoothly and downward gear changes were made at 500rpm less.
    Fuel 3 Same car lost the tendency to stall in the first 3 to 4 kms. Mid range power was also improved.
    Used in an automatic low end torque and acceleration was improved and results were similar to above.
    Maybe these engines were designed to work on 98 octane but driving with these fuels is easier and more fun. The newer ethanol fuels can also give good performance .
    I tried the latest cleaning fuel in my four stroke whipper snipper and the engine stopped running on after the first use. This was so for a while but now returns now and again but the run on is only for a few revs.

Isaac Bober

Isaac Bober

Isaac Bober was born in the shadow of Mount Panorama in Bathurst and, so, it was inevitable he’d fall into work as a motoring writer. He began his motoring career in 2000 reviewing commercial vehicles, before becoming editor of Caravan & Motorhome magazine. He then moved to MOTOR Magazine before going freelance and contributing to Overlander 4WD, 4×4 Australia, TopGear Australia, Men’s Health, Men’s Fitness, The Australian, CARSguide, and many more.