Brake fluid

Understanding Brake Fluid Shelf Life and Other Important Auto Essentials

You’ve probably wondered about the various substances in you garage, specifically brake fluid shelf life. Just how safe is it to use a can or bottle of fluid that’s been sitting in the garage or basement? You’re right to give this some thought, as it’s not just brake fluid, but a number of other automotive fluids and products that have a definite lifespan once they’ve been opened (or even when they stay sealed). Knowing the difference between what’s acceptable to put in your car and what should be disposed of can make a big difference in your vehicle’s performance on the road.

Brake Fluid and Moisture

Brake fluid shelf life is directly related to the amount of moisture it’s exposed to after the bottle has been opened. Brake fluid is hygroscopic, which means it attracts and absorbs water from the surrounding atmosphere. The more water that it absorbs, the less effective it becomes when introduced into your vehicle’s braking system. With water in the mix, the boiling point of brake fluid can be greatly reduced, which given the pressures it’s under during braking translates into less effective stopping power and a spongy brake pedal.

Opened vs. Unopened

When a bottle of brake fluid leaves the factory, it’s sealed so that it doesn’t come into contact with any outside air that might also contain moisture. Most brake fluid manufacturers state that a sealed bottle has no set expiration date. In a sense, the fluid doesn’t break down over time and offers the same level of performance even after years on the shelf.

An open bottle is a different story. Even if you’ve only poured a little out of the bottle, you’ve still introduced moisture into the equation, and the chemical process of absorbing that liquid from the air has begun. Most manufacturers recommend that any open bottle of DOT brake fluid should be used within 12 months, or else discarded. Keep in mind that a full year is the very outside limit of what would be acceptable. A three-month period is more likely to offer a better limit of safety in terms of keeping the boiling point near its original level.

Oil dipstickOil and Power Steering Fluid

Engine oil follows a different guideline compared to brake fluid shelf life. Although moisture isn’t really an issue for oil, the lifespan of the additives packed inside the bottle has a definite impact on how long it can be stored before it should be thrown away. In a stable environment, where temperature doesn’t fluctuate dramatically or reach extremes of cold or heat, you can get about five years out of a bottle of motor oil. Check for an expiration date, as more manufacturers have started to add this to each container. Power steering fluid is a similar story. Unopened, three to five years under normal temperatures is a safe window for use.

Check out all the brake system parts available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on brake fluid shelf life, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Morguefile.

about author

Benjamin Hunting

Having been bitten by the car bug at a young age, I spent my formative years surrounded by Studebakers at car shows across Quebec and the northeastern United States. Over ten years of racing, restoring, and obsessing over automobiles lead me to balance science writing and automotive journalism full time.  I currently contribute as an editor to several online and print automotive publications, and I also write and consult for the pharmaceutical and medical device industry.

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