Leaks - Lethal Ones and Elusive Ones

Leaks - Lethal Ones and Elusive Ones

Some fluid leaks on a car we can live with, at least until we have time to fix them, but there are others that are so dangerous that they require immediate attention. Chief among the latter is a petrol leak.

The only good thing about a petrol leak is that it gives you fair warning by the unmistakeable, strong smell of petrol around the car.

Never drive a car smelling of petrol until you have established where the smell comes from. If it's only the tank that was filled to the brim on a hot day and the expanding petrol is now pushed out of the overflow tube, it's not so bad - except for your pocket and the environment.

But if it comes from somewhere in the engine, don't even think about starting the car.

Petrol around hot engine components is seriously bad news, especially if the odd stray spark is also present. Trace the leak by following the fuel lines and looking for petrol stains, or unions that are moist with petrol.

Brake fluid leaks are almost as dangerous, except that the split braking systems on modern cars provide a margin of safety.

If the hydraulic lines to one set of wheels lose their fluid, you should still have brakes on the other set of wheels. But the overall braking efficiency will not be the same as when all wheels are braking, and in an emergency stop things can go badly wrong.

So if you have a sudden, major brake fluid leak - say from a flexible hose splitting, switch on the hazard flashers and drive slowly, straight to a place where the leak can be attended to.

Coolant leaks can be the devil to pinpoint because they are sometimes pinhole-sized and only visible when the coolant is hot enough for the cooling system to be under pressure. As soon as you switch off the engine and the coolant starts contracting, the pressure drops and the leak disappears.

Furthermore they are sometimes small enough for the tiny jet of coolant to be vaporised by hot airflow before it can leave the tell-tale greenish-white streaks where it runs down. If you have a mysterious, ongoing loss of coolant, pray that it's a pinhole leak rather than an internal leak where coolant seeps into the oil passages or combustion chambers.

Radiator shops will do a pressure test which might show up an external leak. If not, you just have to monitor the situation very closely.

A pinhole will soon enlarge itself enough to remove all doubt, and an internal leak will either leave signs on a spark plug, or the dreaded symptom of water in the oil - a brownish emulsion, looking like mayonnaise - will appear on the dipstick.

The most elusive leaks on a modern car are slow leaks of the air-conditioning refrigerant. Aircon systems circulate a mixture of liquid and gas under high pressure.

Tracing a tiny leak in such a system is made more difficult by the fact that aircon components are located in some of the most inaccessible places on a car - behind the dashboard, between the radiator and the grille, etc.

Various ingenious methods have been tried to trace a refrigerant leak without doing laborious disassembly work.

The propane flame method used a low-volume propane torch drawing in air through a long hose. A technician would place the hose in areas prone to leaks, hoping to draw in enough leaking refrigerant to change the colour of the flame.

This didn't work well for small leaks. Then came electronic gas sniffers, but they were too easily triggered by other gases.

The latest automotive leak tracing technology uses an assortment of safe, non-toxic fluorescent dyes which have the useful property of glowing bright yellow-green under ultraviolet light.

To trace a leak, add the appropriate dye to the fluid that's leaking, wait for a while, then shine an ultraviolet light all along the system. You cannot miss the bright dayglo green under a dark bonnet or in some tight corner behind the dash.

While on the topic of refrigerant leaks, here's a tip from an experienced aircon technician:

A leak often occurs when the film of oil between the compressor main shaft and its oil seal dries out because of the aircon not being used for lengthy periods. To prevent this, switch on the aircon for at least a few minutes every week, even in winter.