Maintenance & inspection
What is a fluid leak?
A fluid leak is any loss of oil, fuel, coolant or hydraulic fluid from a vehicle. Leaks are a roadside prohibition item, an environmental issue, and usually a symptom of something else.
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<img src="https://fleetoptix.co.uk/glossary/fluid-leak/diagram.svg" alt="fluid leak — diagram from FleetOptix" width="880" height="620" loading="lazy">
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<a href="https://fleetoptix.co.uk/glossary/fluid-leak">What is a fluid leak?</a> — diagram by
<a href="https://fleetoptix.co.uk">FleetOptix</a>
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</figure>They are checked by looking under the vehicle before it moves, which is the part of the walkaround most likely to be skipped in the dark or the rain.
A leak is rarely the fault itself. Oil on the ground indicates a seal, a hose or a joint that has begun to fail, and the interesting question is what.
Environmental exposure is separate from the roadworthiness one. Fuel or oil reaching a drain is a pollution incident regardless of whether the vehicle was roadworthy.
What goes wrong in practice
- Checked only where the vehicle is currently parked, missing a leak that appears when running.
- A small leak monitored indefinitely rather than diagnosed.
- Spillage on a yard not treated as a pollution issue.