When considering fuel quality, we’ve always thought first about water, rust, and other impurities in the fuel. Knowing we intended to travel the world and expecting poor quality fuel in the many less-developed countries we would visit, we left Seattle with 48 primary filters on board. What we have learned is that fuel quality is mission-critical in  less-developed countries and, generally, fuel quality has been remarkably good everywhere we’ve been.

In the 10,063 hours we have traveled with Dirona, we have never seen material water in the fuel. We have seen lots of rust and even a fairly large cockroach that came in with a fuel load, but nothing difficult to filter out. All fuel that gets to our Deere 6068AFM75 main engine has to pass through at least four levels of filtration and most fuel burned has passed through three of those filters many times. We’ve had no issues with fuel quality.

In fact, the only time we have a truly poor fuel buying experience was on our previous boat in Northern British Columbia, Canada where we spent more than $5/gal to buy a load of fuel that included several gallons of water, also at $5/gal. It’s nasty seeing all that water in in the fuel system but even in this extreme situation, the filters pulled it out, the engines ran fine, and there were no follow-on issues.

We’ve noticed more recently, however, that there is more to fuel quality than avoiding debris and water in the fuel. The first is oil cleanliness. Our Deere has always produced black oil within minutes of an oil change. It’s not a big deal and it doesn’t indicate an engine problem, but on our engine, the oil just blackens the oil right away.

A weird thing happened over the year we spent in the UK and Ireland in 2017/2018. When we changed the oil, it didn’t blacken for more than 100 hours. Very few things on a diesel engine get better with wear so we were scratching our head as to why an engine with 9,000 hours would suddenly stop blackening the oil.

Another factor magically improved over that year. The dry exhaust has always produced some minor sooting on the boat deck under certain conditions. It doesn’t happen always but there is often minor sooting which, if it doesn’t get cleaned up quickly, even a few bits of soot end up ground in or streaked.  It’s ugly but it’s not that common nor that hard to clean. It’s made us slightly more interested in wet exhaust designs but, other than that, it’s not really been an issue. Many owners are careful to run hard before stopping the boat and to cover the exhaust stack so that water doesn’t run won the pipes. We’re told if you do this, you can virtually eliminate the problem.

On the sooting, another “magic” clean-up happened. Over the last six months in the UK and Ireland, we don’t recall cleaning any marks off the deck or the crane. It’s nice to see, but it seems weird that a 9,000 hour engine would end up improving.

It appears these improvements are due to fuel quality. Most of Dirona’s running hours have been on high sulfur content fuel. As we travel the world, we are often getting 500 PPM to even 1000 PPM. This is within the Deere specification and, for most of these locations, the choice is to take that fuel now or wait at the dock for few years for environmental regulations bring improvements. There are times when you have little choice on a fuel purchases.

John Deere Fuel and Oil Quality Specifications

Before travelling to Norway, we’d burned through 3 tanks of 10 ppm sulfur fuel purchased in Kinsale, Loch Maddy, and Dublin Ireland where Irish fuel standards require that fuel for non-road mobile machinery contain no more than 10 ppm sulfer. It didn’t make much difference at first but, over the six months, the oil stayed clean after a change and there were no soot marks on the deck.

Three months ago we took on a load of fuel in Tromso, Norway way up above the Arctic Circle and we are now back to 500 ppm sulfur fuel. We’ve seen some sooting return and the oil is again black. Our fuel injectors needed replacement at 9,000 hours which we think is respectably good. We suspect that if we’d spent the 9,000 hours on 10 ppm diesel, its possible we would still be running the original injectors.

Fuel quality is not just about avoiding water, rust, and other impurities. Higher sulfur content can increase wear, require more frequent oil changes, blacken the oil, and contribute to sooting.