DIY car maintenance - what not to do

Handling vehicle maintenance jobs yourself can save you money and improve your familiarity with the vehicle you own and drive.

Some owners with more technical and mechanical skills undertake more complex tasks.

But mistakes are easily made and can cause significant issues. It could even result in the voiding of the vehicle warranty.

Here’s a rundown of some common mistakes and how to avoid them.

Oil changes

Oil is the lifeblood of an internal combustion engine, and changing the oil as per the schedule is vital for its continued health.

But so is using the right oil. Your car’s owner’s manual will recommend which viscosity (or thickness) range to use. It will be represented as 20W-50 or similar.

The engine is designed to work with the thickness of oil recommended by the manufacturer.

It’s also imperative to put the right amount of oil in the engine. Overfilling can be just as damaging as running low.

And be wary of electronic oil sensors as they can be faulty. If a sensor fails and oil isn’t added as needed, it could result in serious engine damage.

Of course, you should also change the oil filter when you change the oil. But make sure you fit a new filter ring (and remove the old one) as well, otherwise it can leak oil.

Other fluids

Of course, there are other fluids that need attention in the car such as brake fluid, radiator coolant, power steering fluid, and the windscreen washer reservoir.

Here’s a tip on brake fluid: if you’re fitting new brake pads, rotors or shoes, then drain some fluid from the master cylinder or you’ll have the master cylinder reservoir overflowing.

Wipe off any excess quickly because brake fluid strips paint.

If you’re refilling the radiator, make sure you don’t leave large air pockets in the system. This is a potential issue because in modern cars the radiator cap is not always the highest point in the system.

Be aware that some cooling systems do not have drain plugs. These vehicles need to be serviced by qualified technicians with correct specialised equipment.

Look for bleed screws or jack the car up (or park across a hill) to ensure the cap is higher.

Make sure the new coolant matches the specification recommended by the car manufacturer.

Spark plugs and electrical

While spark plugs may be simple to replace on some vehicles, they can be complex on others, requiring the removal of multiple components to get access.

Specialist sockets may be required to remove the plugs, and if you don’t know what you’re doing or use the incorrect tools, you run the risk of snapping a plug or damaging other nearby components.

If you know it’s been a long time since the plugs were removed, then get some penetrating fluid (like WD40 or CRC in there to help.

On the topic of vehicle electrics, when working on the car don’t forget to disconnect the 12V battery by removing the negative terminal (black, -) first. Removing the positive (red, +) first might create a short circuit or cause a nasty arc flash.

Some vehicles are equipped with security codes for radios and will lock the radio if the battery is disconnected. Be sure you have the radio code to insert back into the radio once the battery is fitted. This also applies when changing a battery.

And if you’re changing a battery, make sure your replacement has the correct Cold Cranking Amps (or CCA). Sophisticated electronics also mean the battery could need to be coded to the car. Incorrect fitment could cause starting problems and even fry the engine control unit (ECU).

Timing belts

Carrying out a timing belt replacement correctly also includes replacing pulleys, drive belts and tensioners, as well as the timing belt.

A mechanic will often recommend replacing the water pump at the same time to save money should the pump fail in the future. That avoids the cost of the components needing to be removed and replaced again.

Timing belt replacement requires specialist tools. Simply marking up by eye can cause significant issues if the teeth on the cam pulleys are not lined up correctly. Unless you’re very experienced, leave this one to the professionals.

Don’t void your warranty

If you’re servicing a vehicle within its initial manufacturer warranty period, bear in mind that servicing work must be carried out within specific time frames and by qualified technicians to retain warranty coverage.

Check your service handbook. The scheduled service may require an air/cabin/fuel filter replacement or spark plugs. It may also be due for a transmission service. These items must be addressed on schedule.

People also sometimes make the mistake of ordering parts based on the year the vehicle was first registered. Using the VIN number is the correct way to go about it.