Hydraulic fluid is vital to keep a dump truck, tow truck, or any other heavy-duty vehicle with a hydraulic lift system functioning. 

In this guide, the experts at Point Spring & Driveshaft Co. answer your questions, laying out how to resolve frequent hydraulic fluid issues faced by trucking professionals. 

Understanding Hydraulic Fluid: Maintenance, Storage & Replacement 

Can Hydraulic Fluid Go Bad?

Yes. Unfortunately, hydraulic fluid naturally degrades over time.

Moreover, several factors can cause hydraulic fluid to degrade more quickly. Certain elements can change it into a useless or even destructive substance. The majority of problems are the result of inadvertent chemical reactions.

What Causes Hydraulic Fluid To Go Bad?

Hydraulic fluid most often goes bad due to contamination or extreme temperatures. 

Contamination

Contamination is the inadvertent mixture of hydraulic fluid with another chemical or compound. This causes an undesirable chemical reaction.

Frequently, the contaminating compound is free water, air bubbles or foam, cleaning solvents, or metal or rubber particulates. Contamination typically happens due to cavitation or aeration of the hydraulic fluid’s container. 

Extreme Temperatures

When hydraulic fluid is overheated, it begins to thin. As it thins, it becomes ineffective as a lubricant. Conversely, over-cooling hydraulic fluid thickens it. If it becomes too viscous, it gums up the machinery.

Extreme heat exposure begins to oxidize hydraulic fluid, permanently altering its chemical composition. 

Can Hydraulic Fluid Freeze?

Yes. The freezing point of hydraulic fluid is -10℉ (-23℃). 

Hydraulic fluid thickens above its freezing point. To keep it functional, use a heating solution while the fluid is in use. Be sure to store the fluid and the equipment at room temperature. 

How Often Does Hydraulic Fluid Need to Be Changed?

Even in the optimal environment, hydraulic fluid breaks down over time. So, machinists recommend changing the hydraulic fluid in the average truck’s system every 2000-3000 hours of use.

That said, the frequency is highly dependent on truck type and use. For instance, most skid steer loaders need to replace hydraulic fluid every 1000 hours, whereas certain dump trailers can run about 5,000 hours between changes. 

Environments that pose a risk of oxidization or contamination, exposure to extreme temperatures, and heavy use can cause hydraulic fluid to “go bad” more quickly—thus requiring more frequent fluid changes. 

Low Fluid, Bad Fluid FAQs

What Happens When Hydraulic Fluid Is Low?

Without enough hydraulic fluid, the truck’s system will lose pressure and increase heat generation over time. 

Both issues not only impact performance, but also risk seriously damaging the hydraulic system’s component parts. Inadequate lubrication can cause wear-and-tear damage. Eventually, it creates cavities in fluid tanks, risking aeration and equipment failure.

How Does Bad Hydraulic Fluid Affect Your System?

Bad hydraulic fluid doesn’t effectively lubricate or cool your truck’s hydraulic system. As a result, performance can become poor. The system may overheat, and the excess friction will likely damage the cylinders and related system components.  

Signs Your Vehicle’s Hydraulic Fluid Has Gone Bad

When hydraulic fluid goes bad, there are often noticeable symptoms. If you see, smell, or otherwise experience the following effects of hydraulic fluid degradation, it’s wise to investigate them. 

Hydraulic Fluid Discoloration, Cloudiness

Hydraulic fluid should be a translucent liquid. It’s typically clear, amber, or pale yellow in hue.

A milky or cloudy fluid usually means water contamination, while a dark or discolored fluid could indicate other contaminants or degradation. If it looks “foamy” or “sludgy,” it’s likely contaminated with air or particulates. 

Unusual Scent

A strong, unusual odor from the fluid can indicate chemical breakdown. Often, this is a smell similar to wood varnish or shoe polish, as nitrogen-oil compounds are frequently present in contaminated fluid. 

Slow, Erratic Machinery Operation

If the hydraulic cylinders struggle to lift or load the trailer bed—particularly if their motion is sluggish or jerking—that’s a telltale sign of a hydraulic fluid problem. 

Similarly, if the truck’s lift capacity has diminished, or if it becomes difficult to maintain pressure during operation, it’s time to investigate the hydraulic system. 

High Operating Temperature (Overheating Hydraulic System)

When the hydraulic system as a whole becomes incredibly hot, it’s a sign the fluid isn’t performing its cooling function. This can stem from fluid degradation through contamination, or from thinning. 

Indicators of Low Hydraulic Fluid

A truck's hydraulic system is meant to reuse and recycle hydraulic fluid. Usually, fluid lasts until it thins out. Its natural degradation is slow, and there is still usually a decent amount of fluid in the system by the time it needs to be replaced. While the fluid's chemistry has changed enough to not work well, it's typically still mostly present.

So, low fluid is almost always caused by a leak. 

Leaks can be more problematic than simple fluid degradation. But, they’re also easier to recognize, as indications are more overt. 

Whirring, Knocking, or Gurgling Sounds

Leaks often let air in as much as they let fluid out. When air gets into the hydraulic system, it typically creates new space and alters the sound of the system's components. Unusual sounds like whining, knocking, or gurgling from the pump are clear signs of a leak. 

Low or Reduced Fluid Level in Reservoir

The hydraulic fluid reservoir is typically set under a truck’s steps. You can check the fluid’s levels through a transparent “sight cap,” which enables a clear sight line of the container without necessitating exposing the fluid to air. 

If the fluid is not filled to the “full” line on the stick marker, it’s low. 

Low hydraulic fluid stores in the reservoir is an unambiguous sign of a leak. That said, the leak’s location may not be obvious. 

To replenish the reservoir, you’ll need to access it from under the truck. Do not fill the reservoir higher than the “full” marker.

Visible Leaks

Visible fluid leaks are the most overt sign of low fluid. Check for leaks by inspecting the space around hydraulic lines, cylinders, or connections. Often, hydraulic fluid that leaks can create a “slick” on the garage floor. 

Signs a Vehicle’s Hydraulic Pump Has Problems

The symptoms described in the sections above can indicate a problem with your hydraulic fluid. They can also point to a problem with your truck’s hydraulic pump.

Visibly leaking fluid, poor performance, and grinding sounds can stem from a damaged pump, particularly one with loose or degraded components. If you also note strong vibrations, that can indicate component misalignment and, at worst, vapor dissolving in the fluid.

If the system as a whole is extremely hot, that can indicate the fluid isn’t reaching where it should—often a problem caused by a faulty pump. 

Thus, checking the pump is key to addressing hydraulic fluid issues. 

How to Troubleshoot & Solve Hydraulic Fluid Issues

At Point Spring & Driveshaft Co., our technicians have extensive training and hands-on experience. Thus, they're empowered to deliver expert hydraulic fluid services—including comprehensive hydraulic system assessment, efficient troubleshooting, and targeted leak repair. 

Efficient troubleshooting begins with visual inspection for leaks, temperature and pressure data analysis, and observation of the fluid's condition. Then, each hydraulic system component is examined in order. Any damaged or loose components are noted, and all repairs and replacements are made to prevent leaks. 

Once the core problem is solved, keep your truck’s system in tip-top shape by scheduling regular hydraulic fluid changes. 

Solve Hydraulic Fluid Problems With Point Spring & Driveshaft Co. 

If you need to replace your hydraulic fluid, identify the source of fluid loss, or simply assess the cause of any fluid trouble, why not work with the experts?

At Point Spring, we never cut corners. We work with clients to develop pitch-perfect solutions to any problem a truck throws at us. Contact us today by calling 888-787-7746. Or, fill out the contact form below.