Changing an oil filter

Fitting a cartridge-type filter

Fitting a new disposable cartridge is a simple task, but you must make sure that the new sealing ring that comes with it is correctly fitted in its proper place, on the inner end of the cartridge. Smear its outer face with clean engine oil.

Screw the cartridge into the side of the crankcase by hand until the sealing ring just contacts the flange, then tighten it another three-quarters of a turn, enough to compress the rubber to make an oil-tight seal. Do not overtighten, as this will distort the seal and cause an oil leak.

Fitting a new element into a replaceable-element filter

Fitting a new element begins with replacing the oil-sealing ring: a new one comes with the element when you buy it.

Fit the ring carefully into its groove in the mounting flange, making sure that it is not bunched or twisted.

Smear its outer face with clean engine oil.

A light spring is fitted below the element and a large locating plate which supports the element.

Insert the new element into the filter bowl and hold it against the mounting flange. Locate the central bolt and engage the first few threads with your fingers.

Tighten it with a spanner, only enough to compress the sealing ring. Do not overtighten or the seal may be distorted and oil will leak.

Refilling with new oil

The quantity and grade of fresh oil you need should be noted from the car handbook before draining. The oil is usually cheaper in 5 litre cans.

To avoid spilling any on the engine, put a funnel in the oil filler hole and pour the oil straight from the can or from a smaller measuring jug. Some cans have a pull-out plastic spout.

If you use the can, pour the oil in small amounts, taking frequent dipstick readings until the level is just above the Full/Max mark.

Allow time for the oil to drain into the sump so that the readings are correct.

A measuring jug enables you to pour in the exact amount required, allowing for the new filter, but always double check with the dipstick.

Once the sump is filled to its correct level, restart the engine and allow it to idle for a few minutes. Check for leaks from the filter sealing ring and the sump drain plug, and tighten them if necessary.

Stop the engine and wait a minute for the oil to drain back into the sump, then check the oil level again with the dipstick.

If necessary, add more fresh oil through the funnel. When the level is correct, remove the funnel and replace the oil filler cap to complete the job.

Cleaning the oil-filler-cap breather

This job is necessary only if the oil filler cap acts also as the crankcase breather (See Checking the emission valve and breather).

Three types of breather filler cap are most commonly used:

• A sealed one with a wire-gauze filter inside the body;
• A plastic one on some cars (Fords) which can be separated to get at the filter inside the body;
• A metal or plastic cap without a filter, but with small air-restricting holes.

They should all be cleaned at least once a year to remove the gradual build up of road dirt around the breather holes on the underside of the cap, and sludge from the wire-gauze filter inside if one is fitted.

Remove the cap from the engine rocker or cam cover either by simply pulling it off, or by twisting anti-clockwise before pulling, to disengage its 'bayonet' fitting.

The best way to clean all three types is to submerge them completely in a small can of paraffin.

Use a stiff brush to scrub the outside and remove all traces of dirt and grit.

With sealed metal filler caps, work the brush through the breather holes to remove as much dirt as possible from the wire gauze filter inside. Repeat the cleaning procedure inside the cap body tube.

For a plastic filler cap which can be separated, prise off the top to gain access to the wire-gauze filter inside.

Lift out the filter and scrub it thoroughly until it is clean. Clean out the filler-cap body and top.

Filler caps without a filter inside should have their small air-restricting holes carefully probed, to see that they are not blocked with dirt and sludge.

Clean the cap thoroughly with the brush, and probe the holes clear with a piece of wire.

On all types of filler cap, flush out the inside with petrol or paraffin. If you have a foot pump, blow the inside of the cap and the filter dry.

Otherwise allow them to dry naturally, giving them an occasional shake. If you use petrol, make certain it has all evaporated before you refit the unit.

If a removable wire-gauze filter is fitted, be sure to put it back before pressing the top cap into position.

If the cap has a sealing ring, make sure also that it is in good condition before you put the cap back on.