What you can get from a multigrade viscosity hydraulic fluid.
by Jim Carroll
November 16, 2018

In business, every cent counts toward a company’s bottom line. This is especially true when the business in question relies on the use of heavy machinery. Every cent that is not spent on repairing equipment is another cent that can go toward profit. The potential for generating revenue increases exponentially when heavy equipment can be kept running longer and is more resilient, avoiding the need for offline maintenance.

Of course, managers have to consider which maintenance costs are worthwhile. After all, spending money on aging equipment that may suddenly break down is unlikely to pay off. But cutting corners on some resources can hurt a company’s bottom line more than it can help. One example of such a dilemma is choosing between a multigrade viscosity hydraulic fluid versus a lower-quality and less expensive alternative. While it may sound cliché, the evidence is clear: you get what you pay for.

Perils of Poor Quality

It is not uncommon to hear operators rev an engine on startup, especially when they are using older equipment that is acting sluggish. What they are technically doing is using increased rotations per minute (rpm) to compensate for the thinning of the equipment’s hydraulic fluid in order to get the engine to do the same amount of work as it ordinarily would if it had a higher-quality hydraulic fluid. Whether the equipment is powered with diesel or electricity, that operator is paying an energy penalty when they increase rpms. If the viscosity of the hydraulic oil were to retain its grade, then the engine could do the same amount of work with less energy—i.e., the operator would not have to rev the engine.

Sluggish starts and performance are just a couple of symptoms related to lower quality hydraulic fluids. Another major indicator can include excessive chatter and vibrations as the equipment’s actuator is being engaged. This is often caused by cavitation, or a lack of sufficient oil in the pump. Cavitation results from a lack of fluid going into the pump and is usually attributed to poor viscosity—either because heat has caused the hydraulic fluid to become too thin to provide enough protection, or because cold temperatures have caused the fluid to thicken to the point that it does not adequately flow. Cavitation results in excessive wear in the pump and greatly increases the potential for catastrophic equipment failure.

Varnish buildup can also have a dramatic effect on equipment performance. Varnish starts as a sticky-soft residue tenaciously clinging to metal. The sticky-soft nature of the varnish attracts wear debris while preventing antiwear additives in the oil from attaching to the metal, thereby dramatically increasing wear. Varnish buildup leads to a chain reaction within the hydraulic system that results in erratic operation, increased wear on valves and pumps, shorter fluid life due to increased oxidation, less fuel efficiency and increased downtime.

Another issue related to hydraulic fluid quality is leaks. Leaks often result from seal failure and ruptured hoses, both of which can be caused by excessive operating temperatures. Seals and hoses are both made from rubber, which crystallizes and becomes brittle when exposed to extreme heat.

Excessively high temperatures can be avoided by maintaining correct volumetric pressure. One of the best ways to modulate volumetric pressure is by using fluids that maintain their viscosity in extremely hot conditions.

Formula for Success

It is important to identify the signs indicating inferior-quality hydraulic oils, but knowing what to look for in a superior hydraulic oil can keep managers from being put in that position in the first place.

Viscosity—a fluid’s resistance to flow—is the most important criteria to evaluating hydraulic fluid performance. After all, hydraulic systems are all about flow. Keep the lubricants flowing, and the equipment pumps will more efficiently deliver better and more consistent performance.

A fluid’s viscosity changes as temperatures increase or decrease—the higher the temperature, the thinner the oil and, consequently, the lower the viscosity. Cold temperatures have the opposite effect of thickening the oil and raising viscosity. This change in viscosity in a given fluid determines its viscosity index (VI). Hydraulic fluids with a high VI will maintain the same viscosity over a wider range of temperatures, resulting in better efficiency, less fuel consumption and decreased maintenance—all of which contribute to keeping the equipment running more efficiently with less downtime.

Another key attribute in superior hydraulic fluids is the use of a superior base stock. Fluids that use a higher-quality base stock have inherently higher VI ratings, so they are less likely to lose viscosity as operating temperatures increase. As a general rule, synthetic hydraulic fluids will always provide a higher VI than petroleum-based fluids. Even the best petroleum-based hydraulic fluid will not have as high a VI as a synthetic fluid, due to the nature of the molecular structure of the base stocks involved.