How to spot tampering with anti-siphon devices
Fuel theft remains a costly problem for many operators, especially anyone managing fleets or heavy plant machinery. That’s exactly what we’ve designed our anti-siphon devices to address here at TankSafe – particularly our TankSafe Optimum. Often, the sight alone is enough to act as a deterrent, but occasionally there are some people who prove a little more tenacious, especially if they’re skimming from inside the organisation.
It helps to know what signs to look for before the damage spreads, the losses mount, or the situation escalates. Drivers, mechanics, and depot supervisors all need to inspect fuel security systems regularly and deliberately. Tampering may not always be obvious, especially when thieves work quickly and try to avoid leaving evidence. Every person who interacts with the vehicle or plant should know exactly what to look for and report anything that looks off, even if it seems minor at first. So, here’s what to watch out for.
Look for signs of forced entry around the filler neck
Workshop teams and drivers should start each inspection by looking closely at the filler neck and surrounding panel. If anyone has tried to force entry, they’ll often leave behind visual signs – a bent neck, scratches on the paint, or warping around the fuel cap recess. Drivers doing daily walkarounds should check this area before and after every shift. If the vehicle is left unattended in a public area or on-site overnight, the chances of tampering increase, so you need to check more often.
Yard supervisors can also review CCTV coverage if the vehicle was parked in a known blind spot or isolated bay. A tamper attempt might not succeed, but even partial damage to the filler neck can let water or debris into the tank. Mechanics in the workshop should document all visible damage immediately and tag the unit for deeper inspection if they suspect forced contact. No one should assume that small marks are accidental – treat every scrape as potential evidence until proven otherwise.
Check for loose fittings or misaligned caps
Drivers and fuelling operatives must always check that the anti-siphon device is seated properly and that the fuel cap fits flush. If someone has tried to lever out the device, it might sit slightly raised or appear to rock in place. That gap gives away the attempt. Fuel caps may also fail to sit straight once tampered with, especially if a thief used a pry bar or screwdriver to gain leverage.
Any cap that no longer clicks tightly or shows resistance during removal needs to be flagged. Mechanics can remove the unit and inspect the mountings directly – some thieves damage internal retaining clips or grind down part of the housing to bypass the mechanism. This sort of tampering often escapes notice until someone removes the part completely. If drivers skip checks or ignore a misaligned cap, the next person might fill the tank without realising they’re fuelling into an insecure system.
Watch out for tool marks or foreign residue
If any prospective fuel thief tries to pierce the anti-siphon cage or grind through its structure, they’ll usually leave behind scuffs, chips, or scrape lines. Fitters and technicians should use a torch to inspect the internal components of the neck, especially in low light. You might find metal shavings, plastic filings, or traces of tool oil. These small signs often point to a failed breach attempt.
Drivers and service engineers must also check for anything that doesn’t belong – glues, foreign sealants, or sticky residues used to hold parts together after forced removal. Some criminals try to put devices back in place loosely so no one notices until it’s too late. If the tank smells strange or shows unexpected build-up around the top edge, someone needs to take the unit apart and investigate properly. It can be a mistake to assume spillage – make sure to check the cause!
Monitor unexplained changes in fuel usage
One good way to cut down on fuel theft is to track average fuel usage for each unit on a regular basis. If one vehicle or machine suddenly shows higher consumption without a mechanical fault or mileage increase, someone should trigger an alert. Many thieves steal fuel gradually to avoid drawing attention – which is exactly the issue with skimming. A consistent drop in miles-per-litre or an increase in top-ups during the week might signal siphoning activity.
Workshop leads can work with telematics data and fuelling logs to identify patterns, and of course, drivers should never adjust or reset logs without supervisor approval. If someone notices missing fuel after a full tank, they’ll need to notify the shift lead immediately. The earlier a pattern is spotted, the better the chance of stopping further loss. Everyone involved in refuelling, from the depot to the field, must treat anomalies as possible red flags.
Your drivers sit on the front line. They see the vehicles up close every day and are the first to notice when something changes. That means they’ll need the proper training to report anything unusual – whether it’s a stiff cap, a strange smell, or signs of interference near the tank. Ideally, encourage a culture of immediate escalation, even for minor issues. It might sound intensive, but it can potentially save you a huge impact on your bottom line.
Supervisors and fleet leads need to make the reporting process simple and direct. If drivers face long forms, delays, or dismissive feedback, they’ll stop reporting. It’s important to act on every report and follow up after every inspection – and make sure the workshop logs each case clearly and adds notes to the vehicle file!
That’s all the essentials in a nutshell. Whatever the case, we’d always recommend reviewing the integrity and condition of your anti-siphon devices on a regular basis. And any of yours are looking like they may be past their sell-by date, we’d recommend upgrading with our very own TankSafe Optimum. It’s the only security device that can offer you 3 in 1 protection by saving you from fuel spills, overfilling, and making your vehicles 100% immune to fuel theft. Our product range is protected by 45 patents covering 49 territories worldwide, so rest assured you won’t find a more efficient and reliable source of protection anywhere else.
If you have any questions regarding any of our products, or you simply need some advice, feel free to head over to our FAQs page, where we answer some of the most commonly asked questions regarding our products and services. However, if it doesn’t address your queries, you can give us a call on 01253 400 401, and we’ll be happy to help however we can!