Why Is My Motorcycle Leaking Gas or Oil? Causes, Fire Risk and What to Do

A drip of petrol under the bike, a strong smell of fuel while riding or a patch of oil under the engine are all signs to stop and deal with the problem properly. This guide explains why your motorcycle is leaking gas or oil, the fire risk and what to do on the road. It is not a DIY repair guide: the aim is to recognise the problem, stop safely and tell the bike owner or a workshop. It is based on guidance from the Spanish automobile club RACE (07/10/2026), a motorbike fire-prevention advisory published on the Bac Ninh provincial government portal (Vietnam), and reports from the Vietnamese news sites VnExpress and VietNamNet.

Quick answer

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• Switch off the engine straight away, keep flames and cigarettes away, and do not restart while fuel is still leaking (RACE).
• Do not ride on if fuel is dripping near the engine, exhaust or rear wheel (RACE).
• Common causes: cracked, hardened or loosely clamped fuel hoses, a cracked tank or worn seal, a stuck carburettor float, or an overfilled tank (RACE).
• Why it is dangerous: leaking fuel evaporates and can ignite when it meets the heat of the engine (VnExpress).
• If the bike catches fire: never use water on a fuel fire (Bac Ninh fire-prevention advisory).
• Rental bike: call the owner and do not remove fuel hoses or the carburettor yourself.

Why is a fuel leak dangerous?

According to VnExpress (02/03/2012), when fuel escapes, evaporates and meets the high temperature of the engine, it can ignite, and leaking fuel easily forms a mixture rich enough to burn. RACE (07/10/2026) also stresses that petrol is flammable and can fall onto hot parts. When unburned fuel reaches the exhaust (because of a rich mixture, weak ignition or a leaking injector), RACE warns of backfiring, overheating, damage to the catalytic converter and oil dilution.

Common causes of a motorcycle fuel leak

Location	Possible cause	Source
Fuel hoses	Cracked, hardened or loosely clamped hoses; old fuel lines with cracks that open at the joints	RACE; Bac Ninh advisory
Fuel tank	Cracked tank or worn seal	RACE
Breather	Tank overfilled; blocked breather pipe	RACE
Carburettor (older bikes)	Stuck float, worn or non-closing needle, loose drain screw	RACE
Air filter	Filter soaked with fuel	RACE
Fuel quality	Poor-quality fuel ageing the fuel system and causing leaks	VnExpress

A crash or a drop can also damage the fuel hose or tank; see what to check after dropping a motorcycle.

What to do as soon as you see a leak or smell petrol

1. Switch off the engine and keep the bike away from flames; do not smoke nearby (RACE).
2. Close the fuel tap if your bike has one (RACE).
3. Stop somewhere ventilated and safe from traffic, then look for the source without touching the hot exhaust or engine (RACE).
4. Do not restart while fuel is still leaking, and do not ride if it drips near the engine, exhaust or rear wheel (RACE).
5. Take the bike to a workshop to check the tank, hoses, carburettor or fuel injection (RACE). On a rental, call the owner first for instructions.

The fire-prevention advisory on the Bac Ninh portal adds that if a bike shows unusual signs such as hard starting, strange engine noises or flickering lights, it should be taken for inspection immediately.

What if the motorcycle catches fire?

• No water: when there are signs of a fuel fire, never use water to put it out.
• Use a fire extinguisher if one is available; it is the effective way to put the fire out.
• Raise the alarm to people nearby, move nearby vehicles away from the fire and ask people to evacuate the danger area.
• Call the fire and rescue police straight away.

These steps follow the motorbike fire-prevention advisory published on the Bac Ninh provincial government portal. Your safety matters more than the bike.

Motorcycle leaking oil: causes and what to do

According to VietNamNet (03/08/2021, citing Lao Động newspaper), oil leaks on motorbikes are commonly caused by:

• The oil drain bolt not being tightened or cleaned properly.
• A cracked engine case after a collision, a drop or an unstable stand, which opens the gasket.
• Sudden temperature changes: washing the bike right after a long ride can also crack the engine case.
• The oil filler cap with a seal that no longer fits.

The article advises taking the bike to a service centre if you lack experience. On the road, if oil gets onto the tyre or rear brake, do not keep riding; call the owner or the nearest workshop. If the engine runs unusually hot after losing oil, see motorbike overheating on a trip.

Preventing fuel and oil leaks before a trip

1. Have the electrical system, carburettor and fuel tank serviced regularly (Bac Ninh advisory).
2. Keep the bike clean so fuel leaks are easier to spot (Bac Ninh advisory).
3. Do not modify the wiring or fit fuses incorrectly (Bac Ninh advisory).
4. Do not overfill the tank (RACE).
5. When you collect a rental bike, look underneath and check for any smell of petrol.

If the bike also loses power or stalls, see motorcycle losing power on the road. Renting for a long trip? Ask Mr Tú – Old Quarter Motorbike Rental how to reach them if the bike has a problem on the road.

Frequently asked questions

Can I keep riding if my motorcycle is leaking gas?

No: RACE advises not restarting while fuel is leaking and not riding if it drips near the engine, exhaust or rear wheel; take the bike to a workshop or call the owner.

Why does my motorbike smell of petrol?

Possible causes include a cracked or loosely clamped fuel hose, a cracked tank or worn seal, an overfilled tank, a stuck carburettor float or unburned fuel reaching the exhaust, according to RACE.

Can you put out a motorbike fuel fire with water?

No. The fire-prevention advisory on the Bac Ninh portal says never to use water on signs of a fuel fire from a vehicle; use a fire extinguisher and call the fire service.

Why is my motorcycle leaking oil?

According to VietNamNet: a loose oil drain bolt, a cracked engine case after a crash or drop, washing the bike right after a long ride, or a worn oil filler cap seal.

Sources checked on 13/11/2026: RACE (07/10/2026), why a motorcycle leaks fuel (Spanish); Motorbike fire-prevention advisory, Bac Ninh provincial portal (Vietnamese); VnExpress (02/03/2012), types of vehicle fires in Vietnam (Vietnamese); VietNamNet (03/08/2021), motorbike oil leaks: causes and fixes (Vietnamese).