With blocked diesel filters causing severe problems for machine operators across the country, FCA England chairman Simon Bowes turns a spotlight on fatty acid methyl ester (FAME), suspected to be the root cause of the issue.

“FAME! I’m gonna live forever!”

You have to be of a certain age to recognise the lyric. Irene Cara sang the theme tune to the 1980s TV show about a performing arts school where there was lots of singing and dancing. I remember the leg warmers it made popular – something I never understood but which was adopted by nearly every girl I knew, including my girlfriend at the time.

But no, it’s not that Fame we’re interested in. It’s something called fatty acid methyl ester and it’s causing all sorts of problems for forestry contractors, farmers, plant companies, quarries – in fact anyone running heavy diesel-powered machinery fuelled by what we commonly call red diesel.

FAME diesel is the generic name for biodiesel derived from renewable sources. There was once a local outlet just outside York that sold diesel made from recycled cooking oil collected from local fast food outlets. It was mixed up with various chemicals and sold to the public on a first come, first served basis, but with a limit of 25 litres per visit. I ran an old Transit on it for most of a year with no problems other than people standing at traffic lights sniffing the air, wondering where the smell of chips was coming from. To be fair, the van ran just as well on it as it did on pump diesel. I replaced that van with a newer Transit and although it seemed fine on the biodiesel it only took a couple of weeks before it lost power and stopped. The fuel filter was full of a yellow waxy substance, and once replaced with a new filter the van ran fine again for a couple of weeks until, again, the filter blocked up. I never found out why the first van ran happily on biodiesel but the second one would not.

Forestry Journal: Operators have reported having to replace their diesel filters twice a week or more.Operators have reported having to replace their diesel filters twice a week or more.

This is a story that more and more people are becoming familiar with. I was using almost pure FAME diesel back then and I knew what I was getting. The guy said to try a 50/50 mix and see if there were any problems. He knew not all vehicles liked his special brew. But why should there be issues with red diesel now?

The problem is that mineral diesel, the stuff refined from crude oil, has been classified as dangerous for the environment. This is a bit of a catch-all as road diesel (white diesel or derv) isn’t actually that much of an active climate-change gas producer, but it is bad for human health. It is also a non-renewable resource as crude oil is finite.

In 2006, the British Standard for road and non-road diesel was revised to allow the inclusion of FAME diesel, though it wasn’t included in red diesel at the time. There was a further change in 2011, when the EU ruled diesel must contain no more than 10 parts per million of sulphur. This was ULS diesel or what we now know as A2 class red diesel. Heating oil or class-D red diesel continues to contain sulphur at 100 ppm.

In April 2018, changes to the Renewable Transport Fuel Obligation (RTFO) meant that a target of 12.4 per cent biofuel in diesel was to be achieved by 2032. This is to be introduced in stages: 7.25 per cent as of now, 9.75 per cent in January 2020. Now these changes have been set in motion, it is almost impossible to source diesel that doesn’t contain an element of FAME.

To understand why FAME is causing problems, it’s important to understand what the fuel is made from.

FAME is largely derived from waste cooking oils (just like in the stuff I used to buy), but it can also be made from many recycled fats, including animal fats. This brew has been added into road fuel since 2004, but had been excluded from red diesel because of the cost of the manufacturing process, until 2018.


The most widely publicised problem is that of microbial growth. It is not algae, as algae needs light to survive which isn’t something usually found in fuel storage tanks. There are microbes that grow in diesel tanks, but to understand how this happens there are two further significant properties of FAME diesel that need explaining.

FAME is a food. You wouldn’t eat chips unless they were cooked in an edible fat, and if you can digest it so can the microbes we now find in our fuel tanks.

FAME is hygroscopic. It absorbs water which, incidentally, is another thing those microbes need to survive. If it absorbs water it can also release it again and, coupled with condensation, water ingress through lids being insecure and ingress during filling, a water layer can form on the bottom of tanks that aren’t regularly drained completely.

It is on this boundary between the water and the fuel where the microbes form colonies and where they can produce what has become known as the ‘rag layer’. This is where the microbes live, multiply, thrive and die. If some of these microbes are drawn into a machine’s fuel tank, they will continue to thrive, especially given that the fuel is constantly warmed, and they will clog the filters and fuel lines. It is estimated that a major colony of microbes in a fuel storage tank could consume as much as 1 per cent of the fuel volume (around 10 litres of fuel in a 1,000 litre grab tank).

A problem not so widely known is that FAME diesel is an effective detergent. It will dissolve and free up all kinds of debris that would normally stay put in a fuel tank, including paint, rubber, sediment, etc. It can also damage fuel lines, seals and other components within the high-pressure fuel system. Common rail diesels, which are fitted in newer forest machines, are very susceptible to hard particulate damage. Injectors and pumps operate within very fine tolerances and any damage caused by wear and scoring can have severe effects on performance and fuel efficiency. Eventually, modern control and engine management systems will simply shut an engine down once damage is detected.

Though I’ve already mentioned water as a factor in microbial growth, it is also a significant problem in its own right. Water causes corrosion and while it is suspended in the FAME fuel it can begin to cause corrosion at a low level. If it is dropped out of the mix, then this problem becomes more severe. All machine operators know the misery of trying to start a machine with water in the fuel – draining, changing filters, bleeding, draining again, and that’s in warm weather. Throw a hard frost into the mix and the problems really stack up. It is, however, the corrosion caused by water sitting in pumps and injectors that can be really expensive and a machine manufacturer will tell you their warranty doesn’t cover damage caused by dirty fuel. It is your responsibility to put clean fuel into their engine, if you ever want to claim on the warranty.

The last and simplest problem is that FAME diesel has the annoying property that it can form a gel, which bungs up filters completely. This is akin to the waxing of diesel in very cold weather. I’m old enough to remember adding an anti-waxing solution into the diesel tanks at home on the farm when someone had forgotten to specify a winter mix for the delivery after harvest. Modern winter diesel doesn’t have additives. It is a blend of constituent chemicals with a lower combined gelling point than a summer mix will have. This can be so effective that there is a blend called Arctic diesel that will stay fully liquid to –40°C.

FAME diesel unfortunately contains glycerin, which can begin to gel at relatively high temperatures, even as high as 13°C, and it doesn’t readily re-liquify once the temperature rises again. This process is called soft gelling, in which the fuel doesn’t become solid but it will contain globules of a more viscous fluid, which will become trapped in filters and eventually block them and stop fuel flow. Unfortunately, a filter blocked in this way can appear perfectly clean with only a slight sheen on the surface of the filter element, though that will be quite enough to stop the fuel flowing.

A final sting in the tail where cold fuel additives like those we used to add into diesel are concerned is that they don’t work so well as they did before the change to ultra-low-sulphur diesel.

Forestry Journal: This picture of a blocked filter, which was only said to have done 52 hours, was shared to the FCA Facebook page.This picture of a blocked filter, which was only said to have done 52 hours, was shared to the FCA Facebook page.

All these things added together mean that modern diesel fuel, much like modern petrol, is subject to instability, degradation and a much shorter shelf life than ever before.

This can mean the fuel in your storage tanks quickly begins to produce a sticky varnish, sediment, acids and becomes more viscous even in warm weather. As a rule of thumb, diesel with a FAME element shouldn’t be stored for more than six months, at an ambient temperature of 20°C, but this time is shortened as the temperature rises. In the summer this can be down to four months and, naturally, the end user has no way of knowing how long his delivery of fuel has been sitting in tanks at the refinery or distribution depot.

These periods are much reduced for fuel in a machine’s tank. Diesel is heated and cooled as it circulates within the fuel system and it can quite quickly become degraded. This degradation includes a high hard particulate content caused by wear particles from the mechanical components in the pumps and injectors and contamination by carbon particles created at the injectors.


All things considered, FAME diesel doesn’t have a lot going for it from a machinery operator’s point of view. There is clearly going to be a turbulent period until some of these problems are ironed out. It’s all very well saying that we should just go back to high-sulphur mineral diesel, but we are set down this road and the political will to be green is something that won’t change. There will be a huge outcry from manufacturers of diesel-powered machinery as they find their engines won’t cope with FAME diesel, and of course it will begin to impact on industry.

Farmers have a huge lobby and construction has a voice. Let’s see what happens when road building and upgrading is stopped because diggers and bulldozers are parked up with wrecked fuel pumps.

Forestry, however, is largely ignored. As long as there are woods for people to walk through at weekends, who really cares if hundreds of harvesting jobs stop because of contaminated fuel?

Our only option is to take all the advice we can, and there is plenty out there. Tanks have to be cleaned, and not just once – they need regular draining and cleaning. Filters will need to be changed more often, fuel will have to be used quickly and machines will need filling only when completely empty.

So far, I don’t see any long-term solution other than a wholesale reformulation of biofuel to make it compatible with modern engines or, conversely, fuel systems in modern engines need to be redesigned to cope with the available fuel.

There is a short-term solution in additives. The typical cost of biocides to treat microbial growth is around 1p per litre, with cold-weather additive another 1.25p per litre and cetane booster around 1.25p per litre – so that’s 3.5p per litre, which is a substantial extra cost.

Surely the fact that a thousand-litre grab tank of diesel will need another £35 worth of additives mixed in to make it usable isn’t acceptable.

If we add in the cost of maybe three or four times as many filter changes into the equation, plus the labour costs and downtime, is this fuel actually fit for purpose? I would suggest it isn’t, and the critical factor for me isn’t that it is only a few engines that are affected. Older engines are less dependent on ultra-clean fuel, but they are less fuel efficient, more polluting engines which we’re told should be phased out.

There appear to be more questions than answers here and it’s not down to the end user to provide the answers. All we can do is shout as loudly as possible until someone listens.