Tuesday, March 17, 2020
TAKE CARE OF YOUR DIESEL
The corona virus issue will have a major effect on cruisers and many will be canceling their plans to join their vessels overseas for the northern hemisphere summer. Their major concerns are the risk of contracting the virus, the relative inadequacy of medical facilities in some destinations, uncertainties about medical insurance and repatriation in case of illness, difficulties for their visitors to travel and return to their country of origin, the difficulty in returning should any emergency occur at home, the large scale closure of cafes, restaurants and tourist areas of interest, possible difficulties in obtaining technical assistance should the crisis worsen and the general uncertainty during what is currently an escalating phase.
This is an article we wrote published a while back in Pacific PowerBoat magazine.
Since a large number of diesel engine problems are fuel-related we should always follow best practice procedures in managing our fuel supply; the key areas to consider being monitoring, filtration and rotation.
Fuel Tanks and Filtration
All tanks require an air breather to equalise internal pressure during changes in fuel level and should ideally have a removable inspection port enabling access for periodic inspection and cleaning. The tank's outlet should be situated as low as possible to avoid the accumulation of water and contaminants in the bottom of the tank.
Filtration starts with a “primary” filter to separate any water present and clean the fuel before it reaches the engine, where a replaceable on-engine “secondary” filter provides a final clean before fuel is supplied to the injection pump. If water accumulates in the primary filter's clear inspection bowl we need to identify its cause and resolve the problem.
Many primary filtration systems have a vacuum gauge to indicate when the replaceable filter cartridges should be changed. In any case they should be replaced about annually as the paper filter media can deteriorate after long term diesel immersion. Sometimes it's hard to tell if this gauge is working (Envoy’s needle rarely moved) and you can check this by slowly closing the engine's fuel supply valve (not the return valve) with the engine idling in neutral. You should see the gauge's needle begin to rise confirming a vacuum is present. Every boat should carry several spare filters and every skipper should know how to change them.
While diesel sold throughout Australasia is generally high quality and contamination is rare, this is not always the case in other countries and long range cruising vessels often have a further filtration (or “polishing”) system to polish all fuel into one designated tank (often called a “day tank”) which solely supplies fuel to run the engine(s). The excess fuel from the engine(s) also returns to this tank. Most commercial vessels also use this system.
A long range cruising vessel also generally has a dual primary filter installation so that a filter cartridge can be replaced underway.
For a boat owner the mention of diesel “bug” invokes about the same amount of consternation as osmosis. All diesel carries bug to some extent and the presence of water encourages growth, hence the need to reduce condensation in fuel tanks by keeping them as full as possible. The bug is a fungal organism called Hormoconis resinae (H.res) and is a bacteria not an algae (which would require light). It can normally be seen in filter bowls as black spots or stringy matter. Water and/or hazy, cloudy fuel is also a sign of possible pending problems.
Another issue is asphaltenes (sticky black tar-like particles) which can start to form after about 90 days in unstabilised fuel. You can tell the difference between asphaltenes and other contaminants by collecting a black particle from the fuel filter and putting a drop of acetone or thinner on it. If it begins to melt it’s an asphaltene particle from old, degraded fuel. Bacterial particles also emit a sulphur dioxide (rotten egg) smell.
Aboard Envoy we had a New Zealand-made De-Bug unit installed in the polishing system's fuel input to reduce the chances of diesel bug and either by good luck or good management we never encountered the problem.
We always used a fuel stabiliser when refueling to reduce oxidation, increase lubricity and reduce fuel injector pump and injector wear. It's important to add the correct levels of stabiliser and especially not too much. While stabilisers act as antioxidants they also gradually break down any asphaltine particulates and it's important this occurs only gradually and not suddenly as could happen with excessive additions. Also if too much stabiliser is added any water present may emulsify in the diesel and pass through the filters into the injection pump and injectors where it could cause damage and corrosion.
Additives that deal with water fall into two categories:
The first encourages its mixture with, or suspension in fuel so the water is captured by a water separator or goes to the engine to be vaporised in combustion. These are known as emulsifiers or dispersants or suspension additives. The second category encourages its separation from fuel so it can be drained from a tank or filter. These are demulsifiers.
Some engine manufacturers prohibit using the first option, so only use additives recommended by your engine supplier.
What about bio-diesel?
New Zealand's bio-diesel has a 5 per cent “bio” content (sourced from tallow) and isn't generally sold at marine outlets. Bio-diesel is slightly more hygroscopic than standard diesel although at the five per cent level it is very similar to standard. An industry source informed me that while bio-diesel should preferably be used within six months of purchase it contains additional antioxidant and shouldn't be a problem for up to twelve months. Some commercial operators regularly use bio-diesel and report less emissions and longer periods between filter changes, however unlike privately owned vessels theirs are in frequent use and constantly turning their fuel over.
Maritime New Zealand recommends checking with your engine manufacturer before using bio-diesel. In the Med the commonly sold fuel is 15 per cent bio-diesel and we've used this up to two years after purchase without any issues.
The key point is whatever fuel you are using, monitor it and always use your oldest fuel first.