How To Change Hydraulic Oil In A Gravely Zero-Turn Mower

Upgraded Home Team
by Upgraded Home Team

Zero-turn mowers are enjoyable and can make cutting the yard fun. The mower operates on a hydro transmission that works the right and left sides of the mower separately. Gravely mowers are one of those zero-turns that have been around for over 100 years.

Gravely is a famous brand established in 1916 and continues manufacturing some of the most reliable mowers available.

With every piece of lawn equipment, there comes the time of maintenance. One of those essential things on the list is changing the hydraulic oil and filter. The hydraulic oil keeps the hydro transmission running smoothly the same way it does for a transmission on a car.

Here is how to change hydraulic oil in a Gravely zero-turn mower from the prepping to disposal of the oil. The primary steps include:

  • Draining the oil.
  • Changing filters.
  • Filling the correct oil.
  • Closing the cap tightly.

We will go through each of these steps, tips, and more throughout the article.

Preparing for the Project

There are a few tools you will need to begin this project, along with some safety items. Let’s start with the safety items first. Get some goggles or a face shield for any oil splashing and some latex gloves.

Motor oil seeps into the skin, causing cancer. Most mechanic shops started requiring their workers to wear latex gloves to protect their hands. You will not be able to keep oil from getting on your hands without the gloves.

For the parts, you will need hydraulic oil filters. Some Gravelys have one filter, and others have two separate pumps with filters. The hydraulic oil used is 15W-50 or 20W-50 motor oil.

You will also need a pan to drain the oil and a five-gallon bucket with the cover to store the old oil. At the end of the article, we will discuss the proper way to discard the oil.

The tools you will need are socket and ratchet sets, oil filter wrench, and you may need an Alan Wrench set for some. Not all Gravelys are made the same. It depends on the size of the mower and if it is commercial or homeowners.

Understanding Hydrostatic Transmissions

All Gravely mowers have hydro-gear hydrostatic transmissions. Information coming straight from the manufacturer tells us it provides smoother, improved torque ratings and infinitely variable speed adjustments. The hydro-gear transmissions operate off of motor oil which acts as transmission fluid.

All zero turn mowers have two reservoirs, and some have one or two pumps. The majority has two pumps that power each side of the back wheels individually for steering. Each reservoir has a cold line to show how much oil is needed, and it should get filled to the mark.

When it comes to maintenance, the hydraulic oil and filter need to be changed after the first 75 hours of running. Every 400 hours after the first hydraulic oil change, it should continue on that cycle. Getting some reading done in the owner’s manual can also get you more familiar with the oil change.

The Steps to Changing the Hydraulic Oil and Filter

Here are the steps on how to change hydraulic oil in a Gravely zero-turn mower.

Step 1: Prep the Mower

Park the mower on level ground and jack up the back end. If the mower ran for a while, leave the engine off to cool it off before getting underneath it.

Step 2: Get a Bucket to Catch the Oil

Get a bucket and place it under the drain plug. The drain plug will is located underneath the hydraulic fluid reservoir.

Step 3: Take Off the Drain Plug

Remove the lid to the reservoir to release the pressure to allow the oil to drain freely. Before you unscrew the drain plug, you should clean off the area to prevent contamination. Once the area is clean, unscrew the drain plug with an adjustable wrench or ratchet and socket to release the oil.

Step 4: Take Off Hydraulic Oil Filter and Dry Off the Old Oil

Let all the oil drain before doing this step. Use the oil filter wrench to remove the oil filter and continue to let the oil drain. Clean off all the excess oil when it is finished dripping.

Step 5: Reinstall the Plug and Filter

Screw the drain plug back into place, take some old motor oil, and rub it on the filter gasket. This will make it easier to remove the filter next oil change without the gasket staying behind. Screw the filter hand tight, then use the wrench and turn it 3/4 of a turn.

Step 6: Fill the Reservoirs with Oil

Fill both reservoirs with oil to the cold line. You will need a funnel for this step, and be sure to wipe off any excess oil from spillage.

Step 7: Put the Cap on and Double Check Everything

Replace the cap and screw it on tight. If it is not screwed on tight, air can get inside the lines, or oil can spill out. Turn the motor on to expel air from the lines and filter.

Leave the motor running for about a minute, then shut it off. Go back and double-check the reservoir and the underneath of the mower to make sure nothing is leaking. If you notice the reservoir is low, add some more oil.

Once everything checks out, you can put the mower back down, and it is ready to cut some more grass.

Special Notes and Tips

Here are some things to consider when changing the hydraulic oil.

  • There are 11 different types of Gravely mowers, both commercial and homeowners. Not everyone is made the same.
  • Machines with wheel motors and pumps drain the oil straight from the reservoir tank only.
  • When changing the hydraulic oil on transaxles, the vent plug must remain open when filling with oil.

Why Change the Hydraulic Fluid?

Hydraulic oil keeps the mower operating and steering smoothly. It is a lubricant and keeps the entire hydraulic system going. If the hydraulic oil never gets changed, it will affect the whole system.

Gravelys are expensive and run in the thousands of dollars. The last thing you want is to cut your grass to find out the hydraulic system is messed up. Remember, everything lasts longer when maintenance is a priority.

Many may wonder how long a Gravely zero turn mower will last. The answer is the warranty lasts for 1500 hours. After this time limit, you can expect to have problems.

Keep in mind; the manufacturer may void the warranty if the maintenance is not kept up. After 75 hours and 400 hours, the mechanics can tell if the hydraulic oil has been changed. Some say you can go 1000 hours, but that is not recommended for Gravely.

Hydraulic Oil and Temperature

Many people do not know the temperature affects hydraulic oil. In colder temperatures, the oil is not as efficient as in warmer temperatures. This means it is not lubricating the parts as much as it should.

The hottest temperatures are not suitable for the oil either. In the hottest temperatures, the oil does not distribute evenly among the inner parts of the system. This means the oil will not reach the parts in time to stop damages from occurring.

Here is a tip on how to get the oil right in different temperatures.

  • Check the dipstick before starting the mower.
  • If the oil is too thick, run the mower at idle speed for a few minutes.
  • Running the mower at idle speed will get the oil to all parts before turning it up to full throttle.

Related Questions

What is a zero-turn lawn mower?

Most lawn mowers operate with the front tires turning the mower. With a zero-turn mower, the back tires work through a hydraulic system which can turn the mower in circles.

How long are 1,000 hours for a Zero Turn?

It is difficult to determine how long hours are to months. It depends on how often the mower is used. On average, 1,000 can be about six months during the grass-cutting seasons.

Are Gravelys good mowers?

Considering the competition and how long they have been around. Yes, they are good mowers. However, Cub Cadet has been listed at the top of the list when it comes to mowers.Gravely came in at number six on the list.

Upgraded Home Team
Upgraded Home Team

We are a team of passionate homeowners, home improvement pros, and DIY enthusiasts who enjoy sharing home improvement, housekeeping, decorating, and more with other homeowners! Whether you're looking for a step-by-step guide on fixing an appliance or the cost of installing a fence, we've here to help.

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