How to service the Fuel Filters on a Classic Car

How to service the fuel filters on a Classic Car
How to service the fuel filters on a Classic Car

This guide captures ‘bygone’ advice on how to service the fuel filters on a Classic Car. It is part of a series I am building that describes what to do on a Classic Car Basic Service.

Useful information for Classic Car and Retro Car enthusiasts, as many of these tasks are no longer required on modern day cars.

Remember folks these are ‘bygone guides’ … useful but the safety and personal protective equipment measures are reflective of bygone awareness. Stay safe.





Where is the Fuel Filter on a Classic Car

The petrol filter is part of the petrol pump, which is built into the petrol supply line somewhere between the tank and the carburettor. It traps dirt from the tank before it can reach the carburettor and then the engine.

Any car can suffer from the effects of a dirty petrol tank. An older car will gradually accumulate specks of rust, dirt which gets in through the petrol tank filler, and even shreds of material from tank connections.


When to clean the Fuel Filter on a Classic Car

There is no hard and fast rule on how often the fuel filter should be cleaned because driving conditions vary so much. But a good plan is to check it once in late spring, to eliminate possible summer holiday breakdowns and once more before winter sets in.

Cleaning the petrol filter takes only a few minutes. Finding the pump may take a little longer. It will be either mechanical or electrical.


How to change the Fuel Filter in a mechanical fuel pump on a Classic Car

The mechanical pump is fitted on the engine, usually near the bottom of the crankcase but sometimes much higher-as on the Hillman Imp where it is found on top of the engine.

If it is not immediately recognizable, the fail-proof way of finding it is to trace the feed-pipe back from the carburettor to the pump which, because · it is driven by the engine, must be in its immediate vicinity.

Mechanical pumps usually have a slightly domed cover, held in place by three or four screws. Removing these will allow the dome to be lifted off the pump body exposing the filter.

Mechanical fuel pumps have a domed top held on by a knurled nut. To service the filter start by removing the nut and dome
Mechanical fuel pumps have a domed top held on by a knurled nut. To service the filter start by removing the nut and dome

The filter is a circular metal-and-gauze wafer, and the dirt will be visible on the gauze. The worst of the muck can be removed, carefully to avoid damaging the gauze, with a piece of card, a brush or even one’s finger. A quick swill with petrol will shift the rest.

The filter-a metal-and-gauze disc-is removed next. Clean it in petrol, using the fingers or a brush to remove siubborn dirt
The filter, a metal-gauze disc, is removed next. Clean it in petrol, using the fingers or a brush to remove siubborn dirt

Petrol will tend to dribble out of the pump as the filter is being checked, and this is a fire hazard. Avoid the temptation to use a match or cigarette lighter, even if working on the roadside in a winter gloom.

Be careful not to snag your hands on the retaining screws.

A considerable amount of rubbish can collect in the bowl. Clean it out and wash all components before reassembling
A considerable amount of rubbish can collect in the bowl. Clean it out and wash all components before reassembling

Where is an electric fuel pump on a Classic Car

Electric pumps are more of a problem, since they are independent of the engine and can be mounted almost anywhere. The make of car is unfortunately no guide.

On the Morris Minor, for example, the pump was ideally placed on the bulkhead near the battery, where it could be instantly reached; on the Mini, it is almost inaccessible beside the rear-wheel arch.

The depths of the boot is another favourite hiding place, often made more obscure by some form of shield over the pump.

However, electric pumps give off a rattling noise when the ignition is turned on so can sometimes be found by ear. If not, the only way is to trace the fuel line from the carburettor towards the tank until you see a cylindrical object with an electric wire leading into it.


How to service the Fuel Filter in an electric fuel pump on a Classic Car

An electric pump has two pipes coming from it, one from the tank and the other to the carburettor, and the filter is usually between these pipes.

Before opening the pump, switch off the ignition. The dirt might stop the pump working, since the fuel flow is interrupted, but removing the filter with the ignition on will make the pump start up again and spew petrol everywhere.

One of several designs of electric fuel pumps, which need to be removed from the car for servicing. First open the filter housing
One of several designs of electric fuel pumps, which need to be removed from the car for servicing. First open the filter housing

Quite apart from the dangers of naked lights, a spark from the pump could trigger off an explosion. Also, have some kind of clamp or plug ready – the end of a plastic bag and a rubber band will do – to stop petrol dribbling out of the inlet pipe.

Remove the cartridge-shaped filter, and clean it and the filter housing thoroughly by brushing them with petrol
Remove the cartridge-shaped filter, and clean it and the filter housing thoroughly by brushing them with petrol

Unscrew the pump with a spanner, and clean the filter (which can be a gauze tube or gauze disc) by brushing it lightly with petrol before replacing it.

When reassembling, check that all sealing rings and gaskets are in immaculate order. Replace with new any faulty ones
When reassembling, check that all sealing rings and gaskets are in immaculate order. Replace with new any faulty ones

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How to change an Inline Fuel Filter on a Classic Car

As an alternative to, or sometimes to supplement the filter in the fuel pump filter an line filter is used in some cars.

This takes the form either of a plastic disc about 7.5 cm (3in.) in diameter, or of a length of plastic tube of a wider gauge than the fuel line.

It is inserted into the fuel line near the carburettor. Usually a line filter cannot be cleaned, but has to be replaced. But it is just a few minutes’ work to remove the Jubilee clip at each end of the filter, remove the filter and discard it, and fit a new one.

The replacement does not even have to be identical to the old, so long as its diameter fits your fuel line.

As well as the filters in the fuel line itself, some cars have a small extra filter inside the carburettor just where the fuel line enters it. These need occasional cleaning, and I will cover them in later posts on the servicing of individual makes of carburettor.


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