Car care: Don't take cooling systems for granted

Diagnosing overheating problems and refilling cooling systems correctly is an area that requires skill.

If asked, most vehicle owners would say the cooling system in a motor vehicle has the job of circulating water through the engine block to avoid overheating. Or words to that effect.

So, as long as the water level remains topped up, then engines should never overheat or give any problems - right? Well no, not really.

Cooling systems have come a long way since the very early days when engines relied on a simple thermosyphon circulating system which allowed hot water to flow from the top of the engine block, into the radiator where it was cooled before re-entering the engine at its lowest point. There are now many parts to a cooling system and they all have to work together to ensure engine temperatures and levels are controlled.

Radiator caps, thermostats, hoses, radiator and heater cores, electric fans, water pumps plus the coolant itself (a combination of anti-freeze and corrosion inhibitor), are all vital components and have specific jobs to carry out.

But it's not just about trying to stop an overheated condition. Modern fuel-injected engines are now designed to operate at their peak within a certain temperature range to achieve optimum performance, fuel efficiency and to reduce tailpipe emissions. That means a reduction in warm-up time is paramount, a job largely left up to the cooling system to ensure those ideal temperatures are reached as quickly as possible.

As vehicles age, however, it's only natural cooling systems suffer from deterioration and there is potentially lots to go wrong, such as leaks. The use of plastics in cooling systems can create coolant loss issues with top and bottom radiator tanks and thermostat housings are both well known within the trade as potential problem areas.

Because cooling systems operate under pressure (controlled by the radiator cap) any weak links in the system are quickly found out.

But identifying and correcting a leak only applies pressure to the next weakest point so if one hose for example is showing signs of deterioration or is leaking, then chances are others of similar age will quickly become the next weakest spot.

It's for this reason that most reputable repairers will often recommend other hoses are replaced at the same time to help avoid future cooling system leaks a short time after repairs.

Corrosion within the system is another potential problem area that can produce leaks and other overheating issues and is controlled by having recommended replacement intervals for the coolant itself. Most of the modern fleet now have coolants that will last 10 years or 200,000km (whichever comes first), which obviously helps reduce service costs in the perfect world. Issues can arise, however, when the coolant is drained so other repairs can be carried out or because of an accident resulting in coolant loss.

Using the correct type and amount of coolant is obviously critical to the system being allowed to carry on doing its job properly. For older and high mileage vehicles it could be argued any coolant (amount and type) is better than no coolant at all, but in the main it's best to stick with the respective original manufacturer's recommendations and/or take advice from your trusted repairer.

Any engine overheat should be avoided at all costs. Excessive heat can mean a major internal meltdown which can sometimes lead to repairs costing more than a vehicle's total value.

Diagnosing overheating problems and refilling cooling systems correctly is another area that requires a high skill level. At times, the result of an overheating problem is blamed as being the original cause and repairs are carried out only to fail again a short time after because the original problem still exists.

If repairs involve the draining and refilling of the cooling system, for example, it is not unheard of for head gaskets to fail because the cooling system had not been bled properly and air has become trapped in system. So if you're a home mechanic then be warned; clearly identify the reason for an overheating problem and be confident you can bleed the cooling system properly after repairs are carried out (especially so with a Subaru with its horizontally opposed Boxer engine).

In addition and regardless of who carries out the repairs, check the garage floor for any signs of coolant, the radiator level, plus keep a close eye on the temperature gauge for a week once it's back on the road.

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