Jon Thomas, via carcraft.com: Do automotive fluids in factory-sealed containers have a limited shelf life? For example, I have a bottle of brake fluid that's about five years old. The plastic container has become misshapen, like a vacuum is forming inside (yes, unlikely, I know.) But is it still good? How about motor oil?
On another subject, when do you lube fasteners? What do you use, and where-on bolt threads and under bolt heads? This might make a good article.
Jeff Smith: Jon, any brake fluid has a shelf life that can be directly attributed first to the type of container used. For example, the plastic container that you mention is not as good as metal cans with a pressed-in seal and a screw cap. The fact that the bottle is misshapen probably has more to do with pressure changes than anything else. I have several plastic bottles that have done the same thing that are only about six months old. I spoke with Amsoil and the company says that in its sealed plastic container, the brake fluid is good for two years, stored in a cool, dry location away from sunlight. The company also says the paneling or changes in shape of the bottle are merely cosmetic and have no relation to the quality of the fluid inside. I also spoke with Wilwood brakes and the company representative says that purchasing the smaller brake fluid containers minimizes the loss. So the key here would be to buy brake fluid in small quantities so there's not a larger container sitting around. Also keep the fluid container tightly closed to help with shelf life.
In your case, the problem with even a still-sealed new bottle that is five years old is that the plastic bottle is still slightly porous. Brake fluid is hygroscopic, meaning that it attracts water and will absorb moisture right out of the air. I'm not sure where you live, but let's just say that if you live anywhere that is humid (which is just about everywhere except maybe the desert Southwest or Denver), that the brake fluid in your can is probably contaminated with water. The problem with water in brake fluid should be obvious. Not only does water create rust and corrosion in the brake system, which can lock up wheel cylinders, but water also turns to steam when subjected to temperatures above 212 degrees F-something a wheel cylinder or caliper can easily achieve. Once the water turns to steam, it creates air in the system, which creates a very spongy pedal-something else you don't want. Brake fluid is rated by its dry boiling point. There are several grades of brake fluid: DOT 3, 4, 5, and 5.1. The above chart (courtesy of AfcoRacing.com) illustrates the differences in boiling points at degrees F. Also note the drastic change in boiling points when the fluid is mixed with as little as 3 percent water. With DOT 4 fluid, this small amount of water creates a massive drop in boiling point of 30 percent. This is why it's so important when taking any car to a road course track day where the brakes will be severely heat tested to always completely change and bleed the hydraulic system with new, high-quality brake fluid. DOT 5 brake fluid is silicone based, which is not recommended for any performance application. The only advantage to silicone might be with museum-stored cars that are rarely driven in which the fluid might delay hydraulic circuit moisture damage.
I contacted oil engineer Mark Ferner at Quaker State and he says that when stored inside in a cool, dry place, engine oil has a shelf life of about four years in its original, sealed container. Exposure to sunlight and/or higher temperatures can significantly shorten this time period. Longer than the noted shelf life, additives may tend to fall out of suspension, although higher-quality oils will probably do a better job of maintaining integrity than inexpensive brands. Moisture is also a detractor, which is why it's best to keep the oil in its original sealed container. Also consider that as oil classifications change, oil more than four years old could possibly not be adequate for newer vehicle applications.
Your question about what lubricant to use with fasteners is a highly debated subject. The abbreviated answer is that engine oil is the standard by which all factory fastener torque values are based, but there are numerous variables that affect this torque. Basically, if you coat a bolt with engine oil and then subject it to a sequence of torque and release, the actual clamp load on the fastener will change each time the bolt is retightened, despite the fact that bolt is tightened to the same torque. This is because engine oil will not respond consistently under these high-pressure conditions. ARP just recently introduced a new thread lubricant called ARP Ultra-Torque that is designed to be consistent through numerous torque applications. At least for ARP fasteners like head bolts, this would be the lubricant that we would recommend and what ARP's torque specs will likely indicate. Keep in mind that when you use a torque wrench, a majority of the torque applied to the fastener is used to overcome friction. For a head bolt, for example, friction between the underside of the bolt head and the washer, between the washer and the head, and then between the bolt threads and the block requires some kind of lubricant. Because of the variation in torque readings that occurs during this procedure, many manufacturers are now using what is called torque-angle measurements. This is where the bolt is pretightened to a given spec like 20 ft-lb and then the fastener is turned a given number of degrees-say 90. The pretorque and the angle are established through very specific testing to establish the proper clamp load. This is more accurate because the torque-angle method is not affected by resistance due to friction that affects all torque wrench readings. If there is enough reader interest in this subject, we could do a complete story on how torque angle is a much better way to load certain engine fasteners like head bolts.
Brake Fluid / Dry Boiling / Wet Boiling
DOT 3 / 401 / 284
DOT 4 / 446 / 311
DOT 5 / 500 / 356
DOT 5.1 / 518 / 375
All temperatures are in degrees Fahrenheit. Wet boiling point is brake fluid containing 3 percent water by volume.
Automotive Racing Products (ARP)
We made a quick pass through the all-GM car show at Woodley Park in California's San Fernando Valley and ran across this super-sleeper '62 Buick Special quadra-door. The drivetrain is a 350ci small-block Chevy, 700-R4 automatic and a Ford 8-inch. The owner says it runs 14s at 100 mph.