Check your oil, coolant, and transmission fluid levels often and change them according to the vehicle manufacturer’s maintenance schedule. That message has been drilled into drivers’ heads since the days of Drivers Ed 101, and with good reason. Fluids are a vehicle’s lifeblood, and over time, they are depleted and also wear out.
But what about the so-called “forgotten fluids,” the ones you don’t hear about every day? Their function is just as important as the previously mentioned three fluids, but they can’t provide protection unless their levels are checked often and they are replaced frequently.
Providing protection in the form of lubrication is what comes to most people’s minds when they think about their engine oil, transmission fluid and other lubricants. But that’s just one of a fluid’s many purposes. They also contain detergents designed to trap contaminants and hold them in suspension until they’re removed during the next fluid change, thereby preventing the contaminants from adhering to the surface of the very parts the fluid is designed to protect. Transmission fluid is a good example of a high detergent fluid because of its ability to remove and hold contaminants. Many old-school mechanics, backed by a healthy dose of modern online chatter in vehicle forums, even advocate adding some ATF to the engine before an oil change. The theory is that the ATF’s high detergent levels deliver a superior cleaning performance, removing contaminants and buildup that can affect engine performance. Do you agree? Have you ever tried this? If so, what were the results? (Let us know in the comments.)
Since transmission fluid probably isn’t one that you’ve been neglecting, let’s focus instead on the four forgotten fluids – transfer case, differential, brake, and power steering. If you’ve been neglecting any of these, it could be time for a vehicle fluids checkup.
Transfer case fluid
Vehicles with four-wheel or all-wheel drive have a transfer case on the back of the transmission. Its job is to direct power to the vehicle axles. Because it’s filled with rotating gears that are doing some heavy lifting and need constant lubrication, it needs to contain the right amount, type and quality of transfer case fluid.
Just like your vehicle’s other vital fluids, transfer case fluid degrades over time and needs to be changed. How often depends on a couple factors, including manufacturer’s-recommended guidelines and driving conditions.
Using a ’04 F150 with a 5.4 liter Triton V-8 and four-wheel drive as an example, Ford recommends changing the transfer case fluid at 150,000 miles. Shorter change intervals are recommended if the vehicle is driven through water, such as during stream crossings or when launching or retrieving a boat. That’s because there’s a chance water could seep into the transfer case and degrade the fluid’s lubricating properties sooner.
Because wheels on the same axle don’t always turn at the same speed, every axle needs a differential. On front wheel-drive vehicles, the differential may be housed within the transmission and utilize the transmission fluid. On rear-wheel drive vehicles there’s a differential in the back, and on four-wheel drive vehicles there can be three differentials – one in the front, center and rear.
And, just like the transfer case fluid, differential fluids have to keep all those turning gears and parts lubricated and moving freely. Fortunately it too is usually a high-mileage interval change, but consult and follow specific vehicle-manufacturer recommendations to be sure.
Brake fluid is hygroscopic. Simply put – it attracts moisture. That’s its weakness and the reason it needs to be changed according the manufacturer’s specs. That’s also why, in addition to convenience, the under-hood reservoir is usually see-through, so the level can be checked without removing the cap and exposing the brake fluid to more moisture in the atmosphere. Interestingly, and helping prove the case in point about forgotten fluids, Ford’s online resource that lists the maintenance schedule for an F-150 includes no mention of ever changing the brake fluid, which appears to be an oversight on their part. All brake fluid isn’t the same either so don’t just grab anything off the shelf. Most manufacturers are using DOT 3 or DOT 4 brake fluid, but find out for sure what’s recommended for your vehicle because those brake fluids can’t be mixed with DOT 5 fluid. Here’s why.
DOT 3 and 4 brake fluids are glycol based whereas DOT 5 is silicone based, containing at least 70 percent silicone by weight. Because of its higher boiling point, DOT 5 is often specified for applications that include military vehicles and high-performance race cars. Unlike other brake fluid, it also doesn’t attract moisture and won’t damage vehicle paint if accidently spilled. Before you go out and purchase a bottle of DOT 5 brake fluid however, know that it can only be used when specified by the vehicle manufacturer. Mixing it with other types of brake fluid can lead to system corrosion and failure, and it isn’t compatible with anti-lock brake systems.
Further confusing the naming system is DOT 5.1 brake fluid. This category was created to include glycol-based brake fluid with performance characteristics similar to silicone-based DOT 5 fluid, despite the fact that it doesn’t include any silicone. Unfortunately many people understand – incorrectly – the 5.1 as signifying some sort of connection to silicone-based DOT 5, further confusing the situation. Think of DOT 5.1 as a DOT 4 brake fluid that performs like a DOT 5 brake fluid. Is that as clear as a dirty fluid?
Power steering fluid
Some manufacturers and mechanics say power steering fluid never needs to be changed while others have specific mileage- and/or time-based intervals. All will agree, however, that the level needs to be checked periodically to prevent damage to the power steering pump and to avoid a situation where you’re forced to try and steer a vehicle whose power-steering has failed. Take it from me, it’s nearly impossible, and dangerous. That’s why I’m of the opinion that it’s a lot less expensive to replace my power steering fluid than it is a power steering pump so why not show it some love with a change out every so often?
If you’re guilty of forgetting fluids, take comfort in the fact that you’re not alone. Consult the owner’s manual that’s in your glovebox or available online, ask your mechanic, and check your fluid’s levels and ages. You’ll save money in the long run and drive with peace of mind.
Editor’s note: Stop by Advance Auto Parts for the fluids, parts and tools you need to finish your projects. Buy online, pick up in store, in 30 minutes.