How to Load M18 Milwaukee Grease Gun: DIY Guide

Key Takeaways

• The Milwaukee® M18 grease gun offers three loading options: standard cartridges, bulk suction from pails, or high-speed bulk pump filling.
• Always remove the M18 battery pack before loading to prevent accidental trigger pulls and ensure a safe, clean workspace.
• Proper priming by releasing trapped air through the valve ensures consistent grease flow on the first trigger pull.
• Users should purge the tool when switching grease types to prevent mixing incompatible formulations and maintain peak lubrication performance.
• GenuineTools offers authentic Milwaukee M18 grease guns and power tools at up to 60% off MSRP with a 30-day guarantee.

The M18 Milwaukee® Grease Gun Loads 3 Different Ways

The Milwaukee® M18 Cordless Grease Gun (2646-20) offers three loading methods to suit any job site: standard 14.5-ounce cartridges, bulk suction, and bulk pumping. Cartridge loading is the most common for DIY maintenance, while suction loading allows users to draw grease directly from a pail. For high-volume professional use, the pump-to-filler fitting method provides the fastest refill without opening the barrel.

Properly loading your M18 grease gun ensures a maximum operating pressure of 10,000 PSI and prevents air locks that stall productivity. Regardless of the method, always remove the M18 REDLITHIUM battery before servicing the tool to prevent accidental activation. Once filled, use the onboard air bleeder valve to prime the pump and ensure a consistent flow of grease through the 48-inch flexible hose.

How Do I Load a Grease Cartridge?

For most DIYers, cartridge loading is the go-to method. Standard 14.5 oz grease cartridges are widely available, easy to handle, and keep things clean. This is the method you'll use most often for general maintenance tasks around the garage or workshop.

1. Remove the battery pack. Before doing anything else, pull the M18 battery pack off the gun. This is an important safety step, as accidental trigger pulls during loading can cause serious injury or a grease-covered workspace. Set the battery aside on a clean surface where it won't get contaminated.
2. Lock the rod into the retaining slot. Pull the rod all the way back toward you, then push it sideways firmly into the retaining slot. Make sure it's fully locked in. If it's not properly seated, the rod can spring back unexpectedly, which gets messy and can interfere with cartridge insertion. 
3. Remove the barrel and insert the cartridge. Unscrew the barrel from the grease gun body by rotating it counterclockwise. Once removed, take your 14.5 oz (411 g) grease cartridge and remove the cap from the open end. Slide the cartridge into the barrel open end first. This is a common mistake people make in reverse, which prevents the grease from feeding correctly into the pump mechanism.
4. Remove the cartridge’s seal and attach the barrel. With the cartridge seated inside the barrel, peel off the foil seal from the open (exposed) end of the cartridge. Don't skip this, as leaving the seal on blocks grease flow entirely. Once the seal is removed, screw the barrel back onto the grease gun body clockwise until it's hand-tight and secure.
5. Release and press the rod from the retaining slot. Push the rod back out of the retaining slot to release it, then press it completely into the barrel. You should feel it push against the back of the cartridge follower plate. This step creates the initial pressure that will feed grease toward the pump when the gun is primed and triggered.
6. Prime the grease gun. Reattach the M18 battery pack, then locate the priming valve on the gun body and press it until all trapped air escapes. Hold the hose assembly by the spring strain relief, always pointing it away from your body and anyone nearby. Pull the trigger continuously for 10 to 20 seconds. If grease doesn't appear at the coupler, repeat the priming valve step and trigger again until it flows consistently.

There are three main ways to load a M18 2646-20 Grease Gun

How Do I Use Bulk Grease Suction Loading?

Suction loading is ideal when you're working with bulk grease from a tub or pail. It works best with softer, lower-viscosity greases. This is common in farm, fleet, and heavy equipment maintenance where buying individual cartridges isn't cost-effective. Instead of inserting a pre-filled cartridge, you use the barrel itself to draw grease up directly from the container.

1. Remove the battery, detach the barrel, and submerge it into bulk grease. Start by removing the M18 battery pack completely. Then unscrew the barrel counterclockwise and remove it from the gun body. Take the open end of the barrel and push it down below the surface of your bulk grease. If the open end isn't fully below the grease surface when you pull the rod back, you'll draw air in instead of grease, which means you'll be dealing with an air lock during priming. 
2. Lock the rod and remove the barrel. With the barrel submerged, pull the rod back as far as it will go and push it sideways into the retaining slot to lock it in place. This creates a vacuum inside the barrel that draws grease in as you pull back. Once locked, slowly pull the barrel straight up and out of the bulk grease container. Keep it level to prevent grease from spilling out the open end.
3. Wipe excess grease, reattach to the grease gun, and press the rod in. Before reattaching the barrel, wipe any grease off the outside of the barrel and especially off the threads. Screw the barrel back onto the gun body clockwise until it's hand-tight. Then release the rod from the retaining slot and push it all the way into the barrel until it seats firmly against the grease follower plate inside.
4. Prime the grease gun. Reattach the battery pack and press the priming valve to release any trapped air. Hold the hose assembly by the spring strain relief and point it away from your body before pulling the trigger. Pull the trigger for 10 to 20 seconds. With suction-loaded bulk grease, priming can take slightly longer than with a cartridge because there's more potential for air pockets in the barrel. If grease doesn't appear at the coupler after the first 20 seconds, press the priming valve again and repeat.

Once grease flows consistently from the coupler, the gun is ready to use. It's also worth running a small amount of the grease you've loaded through the gun before actual use. Milwaukee® recommends purging the tool with your intended grease brand to clear any residual grease left from factory testing.

How Does Bulk Grease Pump Loading Work?

Pump loading is the most efficient method when speed matters. Instead of pulling grease in by suction or inserting a cartridge, a grease pump pushes grease through a loader fitting directly into the gun via the loader coupler on the barrel. 

However, there's one important safety rule with pump loading that you must follow without exception: only use low-pressure loader fittings with the Milwaukee® M18 Grease Gun. High-pressure loader fittings can cause excessive pressure buildup inside the barrel, creating a serious risk of injury. 

1. Remove the battery and lock the rod into the plunger. Pull the M18 battery pack off first. Then pull the rod back, but this time, lock it directly into the plunger. This is the key difference between pump loading and the other two methods. This configuration keeps the rod in a neutral position that allows grease to be pushed in from the front without the rod fighting back against the incoming grease pressure.
2. Release the rod without pushing it into the retaining slot. Once the rod handle is locked into the plunger, release the rod. The Milwaukee® manual is explicit here: do NOT push the rod into the retaining slot during pump loading. Releasing the rod/plunger in this locked position is what allows incoming grease from the pump to push it back naturally as the barrel fills.
3. Insert the loading fitting. Insert the compatible loader fitting into the grease gun's loader coupler. Before you connect anything, confirm your fitting is both compatible with the coupler and rated for at least 10,000 psi (690 bar). 
4. Operate the loader pump and rotate and press the rod. Once connected, operate the loader pump until the rod is pushed approximately 8 inches out of the barrel. Then rotate the rod handle to release the plunger, press the rod completely back into the barrel.
5. Prime the grease gun. As a final step, prime the gun using the same method described in the cartridge loading section above.

3 Ways to Load the M18 Milwaukee® Grease Gun: Summary Table

M18 Milwaukee® Grease Guns and Other Power Tools Are Available at GenuineTools

Various Milwaukee® M18 grease guns are available at GenuineTools.

At GenuineTools, we stock the full range of Milwaukee® M18 power tools, including grease guns, for DIYers and tradespeople who need reliable gear they can count on job after job.

Every tool we carry is 100% authentic, factory-sealed, and ships from our US warehouse with 1 business day handling. You get the real thing in your hands fast, with zero guesswork about what's in the box.

GenuineTools offers power tools at a competitive price. 

We price Milwaukee® M18 tools at up to 60% off MSRP, because professional-grade gear shouldn't mean paying a professional-grade markup. 

If something goes wrong, our 30-day money-back guarantee covers you with a full refund on defective or unopened items. We also offer personalized service from real tool experts and special incentives for bulk buyers, so if you need one gun or twenty, we have you covered.

Shop for Milwaukee® grease guns at GenuineTools today!

Frequently Asked Questions (FAQs)

Can you use any grease cartridge in the Milwaukee® M18 Grease Gun?

The Milwaukee® M18 Grease Gun is designed to accept standard 14.5 oz (411 g) grease cartridges. This is the size specified by Milwaukee for the M18 platform and is compatible with most professional and consumer grease guns. As long as the cartridge matches that size, it will fit and feed correctly. 

What happens if you push the rod into the retaining slot during pump loading?

During pump loading, the rod handle is supposed to lock into the plunger, not the retaining slot. If you push the rod into the retaining slot instead, the incoming grease from the pump has no way to push the rod back as the barrel fills. This prevents the barrel from loading correctly and can create uneven pressure inside the gun.

How do you know when the grease gun is fully primed?

Priming the Milwaukee® M18 Grease Gun involves pressing the priming valve until all trapped air escapes, then holding the hose by the spring strain relief and pulling the trigger continuously for 10 to 20 seconds. If grease doesn't appear after the first 20 seconds, press the priming valve again and repeat the trigger pull. Suction-loaded guns often take slightly longer to prime than cartridge-loaded ones because of the higher chance of air pockets forming inside the barrel during loading.

Can you switch between bulk grease and cartridges in the same gun?

Yes. The Milwaukee® M18 Grease Gun is fully compatible with all three loading methods interchangeably. Just make sure the barrel is clean and free of old grease residue before switching grease types, as mixing incompatible grease formulations can cause performance issues and reduce the effectiveness of lubrication on your fittings.

What Milwaukee® M18 Grease Guns are available at GenuineTools?

GenuineTools stocks the Milwaukee® M18 cordless grease gun, available as a bare tool (2646-20) or as the 2646-21CT kit, which includes a battery, charger, and carrying case. If you're setting up your first cordless grease gun or adding to an existing M18 system, there's a configuration to suit your needs and budget.

*Note: Pricing and/or product availability mentioned in this post are subject to change. Please check the GenuineTools website for current pricing and stock information before making a purchase.