If you are losing steering or power on your zero-turn mower, then it could be in need of an oil change. It’s not complicated, but there is an order in which things need to be done. So, before you run to the store to pick up some hydraulic fluid for your mower, there are going to be a few things you need to know first. So, let’s take a look at how to change hydraulic oil in your zero-turn mower.
Can You Change the Hydraulic Fluid in a Zero Turn Mower?
Not every hydraulic transmission is serviceable. So the first question you need to answer is if your mower allows servicing. Non-commercial zero-turn mowers are designed with modern hydraulic transmissions or hydrostatic drives that are usually sealed units and do not allow any form of service.
My best advice is to look up your mower serial number and check to see if your hydrostatic drive can be serviced. If it can, then you can move on to the next step.
When You Need to Change Hydraulic Fluid in a Zero-Turn
Manufacturers recommend varying periods between hydraulic fluid changes, but the general consensus is around every 1200 hours of running time. It’s best that you first confirm this with your owner’s manual because I have seen shorter intervals.
Now, if you have a serviceable system with a fluid reservoir and dipstick, you’ll need to check it at least every 200 hours. If you have a very old machine, you should check the fluid reservoir every 50 hours. Again, it’s safest to confirm these time intervals with your manual.
One point to remember is that good quality hydraulic fluid has a life of around five years. So even if you haven’t used your lawn mower much and haven’t gotten near the servicing time, you’ll still need to change the fluid once you get close to the five-year mark.
Besides changing the fluid because it’s servicing time, you may notice some symptoms relating to the hydraulic system. This usually results in the partial or complete loss of drive and will come down to the lack of fluid in the system, which we’ll come to later.
What You’ll Need on Hand to Change Your Hydraulic Fluid
To change the hydraulic fluid on your zero-turn mower, you’ll need the following tools and parts.
Tools Required to Change a Zero-Turn’s Hydraulic Fluid
- Socket Wrench Set
- Hex Set
- Strap Wrench
- Fluid Catch Pan
- Jack
- Jack Stands
Parts Required to Change a Zero-Turn’s Hydraulic Fluid
- Filter
- Hydraulic Fluid
How to Change the Hydraulic Fluid in a Zero Turn Mower (Step By Step Guide)
Now that you have all your tools and parts, let’s go through the steps required to change the hydraulic fluid in your zero-turn mower.
Jack Up Rear of the Mower
The first thing you’ll need to do is jack up the lawn mower. I like to get the rear wheels at least three inches off the floor. Then you’ll want to use a pair of jack stands to support the mower. Once the stand is in place, you can remove the jack to give you additional work room.
Remove Filter Guard
Under the lawn mower’s rear, you’ll find the hydro motors where the wheels attach to the mower. Each hydro motor has an individual fluid filter hidden behind metal guards—both need to be removed. The guards are usually bolted on and can be removed using your socket wrench.
Loosen Filler Cap
Next, locate the filler cap on the fluid reservoir and loosen it off. It doesn’t need to be removed at this point; just loosen it to allow the oil to drain faster.
Loosen Vent Plug
You will find a vent bolt at the top of each motor. Loosen this so the air can escape when you fill the motor with fresh oil. Typically these bolts use a HEX head and can be loosened with your HEX set.
Remove Drain Plug
Next, you’ll want to locate the fluid drain plug on the bottom of each motor. If you don’t have drain plugs, you can move on to removing the filter. But, for you guys that do have drain plugs, you’ll need to remove them. So, place your fluid catch pan under where the oil will drain, then remove the plug using your socket wrench.
Remove Filter
With the fluid drained from the drain plug, you can go ahead and remove the filter. Just remember to use your catch pan to catch the additional fluid from the filter. Also, use your strap wrench to make getting the filter off easier.
Repeat for Both Sides
Once one side fully drains, you can move to the other side. Repeat the steps required to drain the oil.
Oil the New Filter Gasket
Take your new filter and cover the rubber gasket with fresh fluid. This will stop the gasket from binding up when you install the filter and make it an easier job.
Install New Filter
Screw the oiled filter onto the lawn mower. I usually tighten it with my hands first and then give it a quarter turn with the strap wrench.
Install Drain Plug & Guard
Next, reinstall the drain plugs if you have them and reinstall the filter guards.
Fill with New Fluid
The final stage of the fluid change is to fill the system with new oil. Remove the filler cap from the reservoir and fill it with fluid. I recommend filling it with only 50% of the stated volume and then checking the vent plugs.
Once the motors are full of fluid and have pushed the air out, the vent will begin to leak. This is a good indication of when the air has fully gone. So, continue to check the vents while you fill the system and stop when they begin to leak.
Tighten Vents
Once you see fluid coming from the vents, you can tighten them up using your HEX set.
Complete Filling with Fluid
With the vent closed, you can complete filling the reservoir until the fluid reaches the full mark. When finished, you can reinstall the cap.
Purge the System
Even with all of your best efforts, there is going to be some air left in the system. For those without an auto-purge system, you’ll have to do it manually. So, disengage the hydrostatic drives on both sides and take a seat on the mower.
Purging
Switch on the mower’s engine and engage forward drive. With the motors disengaged, the wheels shouldn’t turn. If they do for any reason, the drives were not correctly disengaged.
With disengaged drives, push forward on both handlebars and hold for a few seconds. Then pull the bars back into reverse drive and hold for a few seconds. Repeat this several times and increase the power each time.
Once done, reengage the drives and repeat the forward and backward process. This time the wheels will turn, so be very careful.
Testing the Zero Turn
Finally, you can remove the jack, stand, and test out the mower. If, for any reason, the drives feel weak with increased power, then repeat the purging process. It can sometimes take a few tries to get all of the air out.
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