Ask the Mechanic: How can I tell an alternator is spoilt?

Hi Paul, two days ago my Mitsubishi Pajero failed to start, I bought a new battery which also failed to start the following day. A nearby mechanic says the alternator is spoilt and needs to be replaced. I would like to know what could have damaged the alternator, how can I know the alternator is damaged is it repairable? Nelson Mukuye

Hello Nelson, the alternator on your Mitsubishi is an electrical generator which converts mechanical energy when it is turned by the car engine to produce electrical energy or alternate current. This electricity charges the car battery to help you start the car and powers all the car electrical consumers such as the lights, power windows, the radio and anything else which consumes electricity.

An alternator can break down when the diodes in its rectifier fail. This is the unit which converts the alternator’s AC (Alternate Current) to DC (Direct Current). A damaged diode can drain current or charge from the battery.

An alternator can suffer mechanical damage of the pulley system which is run by a belt connected to the engine, this usually makes noise as it fails. 

There are symptoms or tell-tale signs that can help you know that your alternator is faulty or not working well such as the permanently displayed battery warning light on your dashboard or the dimmed and flickering your headlights.  

In some cases, car electrical consumers such as air conditioning or the radio and wipers will stop working. In the case of mechanical failure you will hear strange noises. In extreme cases the engine may stall or your battery dies and fails to start. 

The alternator is repairable if you can find a qualified and honest technician with simulating and testing equipment which is used to ensure that the repaired alternator produces the correct voltage to avoid costly damage of the car’s electrical systems. 

A rebuilt alternator should have renewed electrical as well as mechanical components. You have the choice of buying a quality used alternator, remanufactured alternator or the more costly brand new alternator.

That said, there are factors or conditions that can affect the performance of the car alternator even if it is not damaged such as a bad fuse or relay, broken engine belt, dirty or loose battery terminals and damaged car circuits or wiring. These can be ruled out during inspection.

Can I use water as an engine coolant? 

In extreme temperatures, does using water instead of coolant damage my engine? Jacob. 

Hello Jacob, using water instead of coolant to cool your engine will damage your car sooner than later. Plain water tends to overheat, cause corrosion and frictional damage of metal components in the cooling system.

When your car engine is running it produces a lot of heat so it needs cooling all the time to prevent engine component damage due to excessive heat. Changing engine temperatures also causes corrosion and lubrication challenges as the oils breakdown and fail to protect the fast moving parts from metal sheet or frictional damage. 

Engine coolant is designed with chemical additives which give it a higher boiling point than plain water. This allows engine coolant to carry away or transfer heat from the hot engine to the cooling radiator.

Coolant is also blended with anti-corrosion additives to protect the metal surfaces in the cooling system from corrosion damage.

Coolant is designed with a lubricant molecule which prevents metal sheer or frictional wear of moving parts in the cooling system such as the water pump.

What makes my full headlights fail all the time? 

Hi Paul, I usually drive late in the night but often fail to engage my full lights. What makes my full headlights fail all the time? Patrick

Hello Patrick, full head lights or full beam lights are the brightest lights on your car and are angled higher to allow you see further. They are switched on when you flick the head light switch from normal beam to high beam.

A blue head light icon light on the dash board confirms a switch to high beam. There are a few reasons why the headlight full beam may frequently fail. A faulty full beam switch is the most common.

If the full beam switch is faulty, you most likely need to replace the complete light stalk, depending on your car headlight switch gear type. The other likely cause is a faulty circuit to the full beam bulb.

A good car electrician will inspect or test the circuit, contacts and bulb socket in case it is burnt or damaged. Occasionally defective or poor quality full beam bulbs fail sooner or burn the sockets.