Parker United Kingdom

Dealing with Condensation and Filtration Problems: A Guide for Diesel Boat Owners

Dealing with Condensation and Filtration Problems: A Guide for Diesel Boat Owners  - Parker UK - Clean oil in filtersMany boat owners have little choice but to store their boats for fairly long periods of time, such as over winter. Often, that can lead to two major problems – condensation, and fuel condition deteriorating.

So what can be done to help reduce the risk of unnecessary blockages and marine engine breakdowns? The following basic tips are intended to support new boat owners and people starting out on the water.


Condensation can be a big problem for diesel boat owners. Unlike petrol engines, there is no vapour pressure to suppress condensation on diesel boats. So when the tank cools, humid air draws back into the tank and water condenses on the tank walls.

When condensation takes hold, the water in the system can cause all sorts of problems - including rust and corrosion, particulate damage or even diesel bug.

This means it’s important for diesel boat owners to take preventative actions such as:

  • Keeping the tank full – this means there are no spare surfaces to produce condensation
  • Draining off the boat each year – where practical, this option also tackles the problem of potential fuel deterioration (although smaller systems tend not to suffer as much from condensation).

Manufacturers often state that fuel shouldn’t be stored for more than 6-12 months for diesel (and less for petrol), as it will physically start to deteriorate after that time. But for many boat owners, short storage periods can be cost-prohibitive.

If fuel needs storing for a longer period, the easiest way to minimise condensation levels is avoiding big fluctuations in temperature. Many modern tanks are designed to reduce the possibility of condensation – and plastic tanks tend to be affected less than metal tanks – but it doesn’t take the problem away completely; so boat owners should also consider fitting tank insulation, as an extra layer of protection for their craft.

Monitoring fuel quality

Boat owners that travel extensively know that fuel quality can vary widely from one place to another. Some marinas pride themselves on fuel storage and have excellent procedures; but in others, it’s possible to find fuel held in 50-gallon barrels stored outside. And where barrels are stored on their end, water can collect in the top and enter the barrel.

When it’s time to refuel a boat, owners should make sure their fuel comes from a good source. Look for barrels that have been stored on their side, ideally in protected conditions. 

Boat owners putting marina fuel into their tanks may want to consider filtering the fuel as it goes into the craft. The simplest way of doing this is to use a fuel filter funnel with water removal filtration media; or if budget permits, there are advanced electric transfer pumps with inbuilt filters, such as Parker Racor’s FBO fuel filter cart range.  These filters remove contamination and water as fuel is pumped onto the boat – cleaning and conditioning the fuel as it goes on board.

Another option is to commission a third party to clean the fuel. There are companies that will visit a boat storage facility, clean the fuel and then put it back into the boat for a service charge.

What to do when water gets into the tank

A top priority for boat owners is making sure that air or particle contamination from one point is not transferred into the boat system. But it’s still quite common to get some moisture or water in the tank.  And if water gets into the fuel, this can cause all sorts of wear and tear problems, as well as risking the injectors becoming damaged. Burning wet fuel reduces octane levels – and that’s bad news for diesel boats.

Engine manufacturers and boat builders usually put some form of water filter separator on their engine, a prior to the fuel injection or engine itself. That filter’s job is to make sure that water doesn’t get into the engine.  However, it’s useful to bear in mind that build quality can vary; and filters can become overwhelmed and these engine mounted filters can be difficult to change or maintain at short notice. So the number one priority for boat owners should be to have a good secondary water separation and particulate removal system prior to the primary engine filter.

Dealing with Condensation and Filtration Problems: A Guide for Diesel Boat Owners  - Parker UK - Parker Raco Engine FilterThe atmosphere can also be a contributory factor. Most tanks have a vent to allow boat owners to let the air out of the system. So it’s a good idea to invest in a quality vent filter – for example, Racor’s lifeguard fuel/air separator - as this will reduce the amount of air that gets back into the tank. 

If the worst happens and water gets in, there are other options worth considering, such as fitting moisture sensors in the boat’s fuel system, to monitor water ingress and show how much water is in the fuel.

For many small boat owners, that’s not really practicable though. So the first sign of a problem could be when the engine stops. Depending on where the boat is at that time, this can be a minor aggravation or a very maintenance issue. 


Filtration replacement for boat owners 

There isn’t a strict right or wrong way to decide when filters need replacing, so it’s down to individual preference.

Often, boat owners choose to replace filters at regular intervals (say, once a year) based on the amount of time they use the craft or the conditions they sail in.  

This may mean some people change filters when they don’t need to, which could result in unnecessary expense; but arguably that’s preferable to not replacing filters on time and being vulnerable if the boat stops due to a blockage.

One thing is clear – if there’s a lot of water or contamination in a system, it’s important to change filters more often. This means more expense, and a heightened risk of getting caught in difficult situations.

Standby filters

Another common option is to have two filters – a main filter, plus one on standby in case of any problems.  This is known as a ‘duplex system’ and is a little more expensive, as it requires two filters and a valve. 

For owners of larger boats this can be a good option. If the filter gets blocked and the boat won’t start, having a duplex on board means you can switch filters and repair the blocked filter at a more convenient time. And crucially, if the boat is vulnerable (say, due to tides, winds or the need to manoeuvre quickly) it takes just a few seconds to move the lever over and continue the journey.

Quick-change filters

Something else worth considering is the speed and ease involved in filter replacements. Some systems take time to strip down, and boat owners also need to get rid of any fuel already in the system.

But there are modern filtration systems that can be changed in seconds. For example, Racor’s Turbine Series and 800 Series filters have easy-change filter cartridges, which can be kept as spares and easily switched without the need for lots of tools.

With a regular maintenance programme and the right tools, boat owners can enjoy many years on the water. If any owners need help, technical advice or specialist products, any of Parker's authorised marine distributors will be happy to assist.


Going to the London Boat Show?

Dealing with condensation and Filtration Problems: A Guide for Diesel Boat OwnersParker's UK sales company and marine distributor ASAP Supplies are at the London Boat Show from 10 to 14 January 2018. Show delegates are welcome to visit stand LB022 for friendly help and advice on dealing with condensation and filtration problems.





Content by Glenn Crame, technology and market development manager at Parker UK







Related links

Check out more Parker blog posts for boat owners:

Diesel Bug and How to Avoid It: Tips and Resources for Diesel Boat Owners

Water - A Diesel Engine's Worst Enemy

Racor SNAPP Fuel Filtration Specified for New OXE High Performance Diesel Outboard Engine

Fuel Filtration for Marine Applications

Filtration Solutions for the Changing Marine Engine Market

New Design for Small Outboard Marine Filtration Applications - SNAPP Fuel Filter/Water Separator

Clearing the Air on Global Emissions Standards for Non-Road and Marine Diesel Engines


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