A grease gun delivers high-pressure lubricant to machinery bearings through Zerk fittings, and using one correctly means loading the cartridge, priming the system, and pumping with steady strokes until fresh grease appears.
A dry bearing fails fast. A grease gun is the tool that keeps joints, bushings, and fittings alive on everything from a tractor to a truck — but only if the grease actually reaches the bearing. The procedure is straightforward, but skipping one step (priming the air out, cleaning the Zerk) turns the whole effort into wasted strokes. Here is the exact sequence that works for manual lever and pistol-grip guns.
The Right Way to Load a Cartridge
Pull the plunger rod all the way back and twist it to lock the spring in the retracted position. Unscrew the barrel from the head assembly and remove any old cartridge. Take the plastic cap off one end of the new grease cartridge — the open end goes toward the pump head (facing the plunger), and the metal-sealed end faces the barrel cap. Make sure the follower plate sits between the cartridge and the plunger; without it, the plunger cannot push grease effectively. Screw the barrel back onto the head assembly until it is tight.
Priming: The Step Everybody Skips
An air lock in the head means you pump air, not grease. If your model has an air-bleeder valve, open it. Push the plunger into the barrel to force grease forward and expel trapped air. Then pump the lever handle until grease flows steadily from the coupler tip with no bubbles. Once it flows, close the air-bleeder valve if you opened it. A properly primed gun delivers grease on the first stroke to the fitting.
Applying Grease to a Zerk Fitting
Locate the machine’s grease fitting (Zerk). Clean it thoroughly with a rag — dirt pushed into a bearing is the fastest way to damage it. Check for damage and replace the fitting if necessary. Push the coupler firmly onto the Zerk at a 90-degree angle for a firm seal; on lever-type couplers, flip the lever to lock it. Pump with steady, consistent strokes. Stop when you feel resistance, see old grease forced out around the dust boot, or see fresh grease appear. Over-greasing wastes lubricant and attracts dirt. After finishing, release pressure if your gun has a pressure-release valve, then pull the coupler straight off — do not twist, which can damage threads. Wipe away excess grease immediately.
Choosing the correct grease type matters as much as the technique.
Common Mistakes and Safety Notes
- Air locks. Failure to prime or open the bleeder means air instead of grease reaches the bearing.
- Contamination. Dirt, metal slivers from cartridge lids, or uncapped fittings all damage bearings. Clean before every attachment.
- Mixing greases. Different grease types (lithium vs. calcium, or different NLGI grades) can react and cause bearing failure. Use only the lubricant specified by the equipment manufacturer.
- Over-greasing. Pumping beyond the point where fresh grease appears builds excessive pressure that can blow seals.
- Wrong angle. Attaching the coupler at anything other than 90° can block grease from entering the fitting entirely.
- Safety. Keep hands and clothing clear of moving equipment. Mark the grease gun clearly to identify the grease type and prevent cross-contamination.
FAQs
What PSI can a manual grease gun produce?
How many strokes does it take to deliver one ounce of grease?
How should I store a grease gun between uses?
Store the gun unpressurized, lying horizontally in a clean, cool, dry area to keep the oil from bleeding out of the grease. Cover the coupler to keep dirt out of the tip.
References & Sources
- O’Reilly Auto Parts. “Prepare and Use a Grease Gun.” Guide covering loading, priming, and application steps.
- O’Reilly Auto Parts. “How to Use a Grease Gun.” Supplemental instructions for manual and pistol-grip types.
- This Old House. “How to Load and Use a Grease Gun.” Practical walkthrough with tips on air-bleeder operation and over-greasing.