INSTANT EXPERT

BLOWING HOT & COLD

COOLING

You might think that cooling systems have not changed but Rob Marshall finds plenty of them that can catch out the unaware DIYer.

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Even the most ardent internal combustion defender cannot deny that burning fuel to power a vehicle is relatively wasteful. Even the latest motorcar diesel engines struggle to achieve a thermal efficiency of over 40%, meaning that comparatively little of the total relinquished energy drives the wheels. Admittedly, not all of this heat is undesirable. Warming shivering occupants is made much easier, with a plentiful supply of heat being made available to the cabin that would have been shed otherwise. Yet, as excessive temperatures will damage the engine severely, the basic cooling system retains the obvious function of transferring and moving heat energy, using a water-based coolant.

When CO2 emissions became more prominent, carmakers needed to get their engines up to that most efficient temperature quicker than ever. The cooling system’s role of not overcooling the engine and transferring heat energy to other parts of the running gear also became increasingly important. Therefore, a modern engine’s cooling system has more than a single role, which is why ‘thermal management’ is relatively new terminology that describes the system’s function more accurately. Precise thermal management is also essential for high-voltage vehicles, a topic we shall set aside for now.

What goes wrong?

If the engine is overcooled, or overheated, your running costs will increase because of reduced efficiency. While overcooling damages the engines slowly, overheating causes rapid catastrophic destruction.

Therefore, thermal management system checks should be part of your service schedule, even though it is mentioned rarely in official literature.

Coolant is better at seeking-out escape routes than pure water. Apart from puddles being deposited on the floor, dampness and coloured crystals are obvious tell-tale signs of minor leaks. Should the level in the translucent expansion tank bottle be close to the minimum mark, do not add tap water. The different mineral content and pH values will upset the coolant’s delicate balance.

While pre-mixed coolants are easy to dose into the system, provided that the engine is cold, it may be cheaper to buy concentrated coolant and dilute it with distilled water. Even so, a mix stronger than 50/50 can reduce the coolant’s heat transfer properties.

Failure patterns and fitting tips

While modern thermal management systems share the same basic setup as vehicles made many decades ago, subtle developments have crept in over the years. Therefore, the following advice s