Vehicle Maintenance 101: Fluids

Imagine you just took your car to a Shop (Dealership or indepedant shop) for an oil change. You're waiting for your car to be done. THe service advisor walks up to or calls you. They tell you that, because you are at 60,000 miles, you are due for a brake fluid flush, a transmission fluid flush, a coolant flush and a fuel induction service. This might seem like an obvious attempt at getting every penny out of you they can. But, while shops love selling the flushes, they are good for your car.

Trust me, I totally understand the irony of my next statement: The Internet isn't always right. There is actually no such thing as lifetime fluid, be it Transmission fluid, brake fluid, Coolant or Power steering. All fluids, synthetic or petroleum-based, break down over time. Take engine oil, for example. Oil does far more than lubricate the engine. As oil passes through the many passages in the block and head(s),  it picks up foreign material such as tiny metal fragments, sludge, carbon deposits and the like, and carries them down to the oil pan, and ultimately the oil filter where the contaminates are filtered out.

Over time, the Oil tends to break down. In an engine, especially in climates that have radical temperature changes (Like much of the Midwest), the engine oil can go from zero degrees Fahrenheit to 240 degrees Fahrenheit in less than 10 minutes, repeatedly. This causes the chemical compound to change slightly, affecting the effectiveness of the oil itself. Add to this the sediments the oil picks up, as mentioned earlier. Oil manufacturers like Amsoil have handy information pages like this one that goes a bit more in depth on the subject.

This same principle applies to all of the fluids in a car, with the exception of brake / clutch fluid. Most brake fluid, commonly referred to by it's Department of Transportation designation, is a Hygroscopic (Water-absorbing) Glycol-Ether-based fluid. As it heats up and cools down, any water vapor that the fluid absorbs can turn to vapor, which causes the hydraulic system to malfunction. So, over time, the fluid picks up moisture from either condensation in the lines or slight seal seepage. This causes the fluid, normally clear and colorless, to develop a bit of a greenish or amber hue, and eventually a black color. When the fluid changes color, it should probably be replaced. DOT 3, 4 and 5.1 applications are all this way. DOT 5, usually only seen on performance cars or off-road high-heat applications, is silicone-based, and does not absorb water, so DOT 5 can't be mixed with any other type of brake fluid.

Transmission and Power steering fluid have friction modifiers in it to help transmission clutches and bands grab, yet keep things clean and lubricated. Over time, these wear out, and need replacement as well.

So, as I've explained, fluids do break down and need to be checked often. Try checking your oil levels at the gas pump. Some cars need to be at operating temperature, but after enough time has passed for it all to have run back down into the pan. Certain cars, especially Subaru's, need a bit longer for the oil to drain.

I hope this has been helpful.

-Phil