Marine fuel tanks obviously store fuel (either petrol or diesel) on board a vessel. And they’re constructed to withstand the harshest of marine environments, from continuous exposure to saltwater to high humidity plus vibration and hull movement from waves, which stirs up sediment.
So a marine setting means there are unique challenges for fuel storage.
Commonly made from plastic, marine-grade aluminium or stainless-steel, permanent tanks are typically fitted inside the boat’s hull and can hold up to several hundred gallons of fuel.
They’re typically designed to integrate directly with the boat’s gauges, fuel lines and ventilation solutions.
What to watch out for with marine fuel tanks during the summer months:
When you’re using your boat during the hottest season of the year (and we all know how sweltering summer 2026 has been so far), there are a number of things to watch out for that could cause damage and, ultimately, potential engine failure, including:
- High humidity
- Temperature fluctuations which can produce condensation in marine fuel tanks, leading to the pooling of liquid and creating the perfect breeding ground for microbial growth (also known as ‘diesel bug’), which can play havoc with your filters and fuel system, with the resulting slime clogging both primary and secondary filters.
- If a warm summer’s day is followed by a cooler night, partially empty tanks in particular can be especially vulnerable to condensation. For ethanol-blended fuels specifically, the resulting water can separate the ethanol from the petrol, which in turn has an impact on engine performance.
The above factors can contaminate fuel, cause poor engine performance and even failure or corrosion of metal parts.
If your fuel is of poor quality, it may cause rough running of your boat, smoke, a loss of power and other engine problems which could ultimately prove extremely expensive.
What you can do to prevent marine fuel tank problems
The good news is that there are plenty of steps you can take to keep your marine fuel tank in a decent condition over the summer months, including:
- Avoiding condensation:
Your tank should consistently be as full as possible at this point in the year. Having less room for air in your tank will minimise condensation, meaning water isn’t as likely to affect your fuel. If your tank is at approximately 95% capacity at all times, this limits the volume of available air space in which moisture can build up.
This is particularly important in the summer, when temperatures may fluctuate.Another way to prevent water build-up is to check your water separators daily and use a siphon pump or drain cock to get rid of any liquid which has collected in the bottom of your tank.
- Regular checking of full caps and vent lines:
Inspect these for any cracking or blockages. At the same time, position vent loops so that they’re high enough to keep out sea spray and rainwater.
There are also filters available which actively absorb moisture from the air going into your tank.
- Use biocides and stabilisers:
These are important because petrol and modern diesel with biofuel blends degrade pretty rapidly in the summer, certainly at a greater pace than other times of year, leading to the aforementioned diesel bug. But with a marine-grade fuel stabiliser and biocide to stop fuel breakdown and phase separation, you help keep this issue at bay. And a suitable biocide is crucial to avoid fuel blockages, especially ahead of a longer trip.
Use products specifically designed for marine use so that fuel remains fresh and so that your engine doesn’t become clogged. That’s especially the case if your boat has been sitting for lengthy periods without being used.
- Frequent filter inspection:
Both your primary and secondary fuel filters serve as your first line of defence, so look after them well in the summer. Check filter bowls regularly for water and sediment, especially if seas have been choppy since this will stir up whatever is in the base of your tank. Look in particular for dark slime or sludge and aim to conduct daily visual inspections.
- Filter replacement:
You’ll probably need to completely replace both primary and secondary filter elements at least once a year. Make sure that you pre-fill new filters with fresh fuel, so that you don’t get airlocks in the system.
- Fuel ‘polishing’:
If you think sludge may have accumulated, or you could be at risk of water contamination, think about using a professional fuel polishing service.
This comprehensive process will send the fuel through specialist water separators and filters to purify it without the need for disposing of or draining the fuel completely.
It separates water and gets rid of the biological growth that can affect marine fuel tanks.
Summer marine tank maintenance with LV Fuel Services
At LV Fuel Services, we fully appreciate the importance of keeping on top of marine fuel tank maintenance in the summer.
After all, our in-depth understanding of the issues involved is based on many years of experience. And we’re leading specialist providers of marine fuel tank services UK-wide, whether your vessel is a narrowboat, longboat or anything else.
Our suite of marine fuel tank services includes:
- Marine fuel tank cleaning
- Marine fuel polishing
- Diesel bug removal
With our help, you can rid your vessel of sludge, water, sediment and any microbial contamination from your tank to enhance fuel quality, keep your engine safe while minimising the chances of a breakdown on the water.
You may find you need us in particular if your boat has an older fuel system, or if you haven’t been out on it for a while. Owners of vessels contact us with a range of issues, including blocked filters, dirty fuel smoke or generally poor engine performance.
Equally, we can help if your vessel has had water ingress, or is experiencing recurrent contamination.
And, of course, we’ll always put safety above all other considerations.
So request a quote today and look forward to a summer of trouble-free boating.
You can also call 0800 799 9739 or email info@lvfuelservices.co.uk.
