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Why are my car's headlights leaking? Add to ...

My headlights are leaking. What I mean is that there is always moisture inside the headlight unit. I can’t find the hole where the leak is occurring. Any suggestions? – Phil in Coburg, Ont.

There are holes in all modern plastic headlight units, deliberately placed there to allow for the pressure difference between the inside and outside of the units.

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It is common for some moisture to appear, especially if the inside of the unit is warmer than the outside – like what happens to the windows in the car, but the headlights do not have a defroster.

Moisture will often appear on the inside of the lens; this usually happens after the lights have been on and the car parked overnight. As the ambient outside temperature goes up in the morning and the inside temperature of the inactive light goes down, the moisture evaporates.

If you use the headlights, the heat generated usually dries out the inside.

Most cars sold in Canada use partial power from the headlights for the daytime running lights (DRLs) so they are partially heated inside even when the headlights are not on.

If there is sufficient moisture inside, it may run down the inside and out the bottom vent. Some units vent better than others, and some too well. I had a car recently with a little moth inside the lens; it obviously got in through the vent.

You should locate the vents in the light unit and ensure they are not plugged.




I read where turbocharging was becoming the favored way to address the issues of fuel mileage and power, i.e. using a small engine for fuel mileage purposes but turbocharging it to extract the necessary power. I recall stories my dad used to tell of supercharged race cars and airplanes. Is there a reason car makers are not using this method of boosting output? Why has it been abandoned in favor of the turbocharger? – Dereck

Supercharging has not, in fact, been forgotten. Many manufacturers are currently using superchargers. Audi (S-lines) Ford (Shelby Mustang), General Motors (Cadillac CTS-V, Corvette ZR-1), Jaguar (XFR-F, XKR), Mercedes (SLR) come to mind immediately.

But you might notice a trend there: no small engines. The reason is that superchargers extract power from an engine in order to produce more power.

Both turbochargers and superchargers are air pumps that force the fuel/air mix into an engine rather than ask the engine to suck it in, as is the case with the normal combustion process. Turbochargers are spun by exhaust gases while superchargers are driven by a belt, chain or gear off the driveshaft. Because the crankshaft is used to spin the supercharger they extract some power (perhaps two to eight horsepower) from the engine at all times and are thus more commonly found in larger-displacement engines with more power to spare. Look at the list above and the common theme is a big and already powerful engine.

Another factor is that superchargers are generally larger than turbos and thus easier to fit to a larger engine. They are generally located between the banks of cylinders of a V-6 or V-8 engine. Turbos can be very small and are incorporated in the exhaust system.

Rudolph Diesel applied for the first patent regarding a supercharger in 1896. Their development was hastened by the First World War where they were used to extract maximum power from air-cooled aircraft engines. They later came into common use for large trucks and construction equipment.

Send your automotive maintenance and repair questions to Richard Russell at globedrive@globeandmail.com

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