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Advice on fixing your classic.
QMy 1.3-litre Escort MKII smells of petrol when I return to it from a trip around the shops. It starts well, so I don’t think it’s flooding. I can’t find any escaped fuel. Any tips?
AClassics sometimes smell of petrol after a stop when they’re hot. This is due to fuel evaporating from the float chamber of the carburettor: it warms up and readily boils within a minute-or-so of turning the engine off. This is nothing to worry about. Modern cars with their completely sealed fuel systems don’t do this, so it’s quite noticeable by comparison.
Similarly, a smell around a vented petrol filler cap or tank breather is normal – it’s the hot vapour expanding and escaping. A strong and prolonged smell, however, warrants investigation, as it almost certainly indicates a leak. We’ll go over a number of possibilities here, to be as comprehensive as possible.
Petrol smells that get stronger the longer the car’s parked (overnight, for example) are usually caused by a leak below the fuel level in the tank. Gravity pushes the fuel out of rust perforations in the tank, chafed or rusty fuel lines or perished hoses. Make sure all hose clips are tight and the hoses haven’t softened, hardened or cracked around their ends. Fuel hose should be regarded as a consumable item. It should last a good five years – but assume nothing.
A low-mounted pump can leak through a perished diaphragm, both externally and into the sump if it’s engine-mounted. Pumps can also leak from their unions or their detachable top if it’s not screwed down tightly or its seal has deteriorated. Most are designed with an external drain hole to minimise fuel ingress to the sump in the event of diaphragm failure.
A blocked tank breather may provoke leaks. If the car’s parked in the sun or in a garage that warms up during the day, the tank vapours expand and pressurise the whole system. Note, though, that this indicates a weakness somewhere else. Small underbody leaks sometimes don’t drip onto the ground – the petrol’s absorbed by dirt, underseal and wax. Look for stained patches or areas where the underseal looks stickier or blacker.
If the smell seems to be coming from the engine bay, consider that the leak may be finding its way quickly onto the hot engine or exhaust manifold and evaporating off without leaving dampness. Look for resinous brown stains around the pump and carburettor. Staining can build up naturally over the years, so clean it off and see if it quickly reappears.
Feel underneath the fuel pump after stopping the engine and smell the oil when it’s hot to check if the pump is leaking into the sump. Look at the fuel hose
unions in the engine bay. Steel or brass hose stubs are peined into the zinc castings of fuel pumps and carburettors and these can become loose with age and vibration. If they move freely, withdraw them as far as they’ll go with pliers, coat them with threadlock and tap them firmly back. You can try to re-pein them by centre-punching a few times around the circumference – but note that the casting is brittle. Ultimately, the pump or carburettor may need to be replaced or rebuilt.
Don’t discount flooding without checking the float level and the condition of the needle valve – if the needle has a wear ring around its conical end, it may need replacing or re-facing in a drill with a fine file and abrasive paper.