Best Grease for a Grease Gun by Grade, Water Resistance and Heat

You load a fresh cartridge, hook the coupler onto a fitting, pump five times, and nothing happens. Or worse, the grease goes in fine but comes out of the trailer coupler as a milky, runny mess after one launch. Washout often comes down to the grease you load, and a stalled gun after a cartridge change is often trapped air. Both are covered below. The choice of grease matters more than the brand of gun. Here is how to pick the right one and get it into the fittings without fighting the gun.

What Is the Best Grease for a Grease Gun?

For most boaters, the best grease for a grease gun is a waterproof, high temperature NLGI 2 grease in a standard 14 oz cartridge. NLGI 2 is firm enough to stay put in most boat and trailer fittings and soft enough to flow through a manual lever gun and a standard fitting.

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Marine Grease Tube 3oz or 14oz

Stock the grease you need for boat trailers, wheel bearings, hitch balls, bikes, ATVs, and machinery before service day.

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That answer covers most of the fittings on a typical boat and trailer, including steering, tilt tubes, swivel brackets, couplers, winches, and roller shafts. The exceptions are special cases like centralized lube systems, which want a softer grade, or very cold climates, where an NLGI 2 can stiffen up in the gun. A good grease to keep loaded is Better Boat Marine Grease, which is NLGI 2, waterproof, and rated for high temperature, so one gun covers the common grease points on a boat and trailer.

Three specs decide whether a grease fits the job.

• NLGI grade. How thick the grease is. Grade 2 is the default for grease guns.
• Water resistance. How well it resists washout. This matters most on anything that gets dunked or sprayed.
• Temperature range. The temperatures the grease is rated to handle, which depends on more than when it softens. Wheel bearings can get hot on long tows.

Why NLGI Grade 2 Is the Default for Grease Guns

NLGI grade measures grease consistency on a scale from 000 (nearly fluid) to 6 (block hard), and grade 2 is the standard for hand grease guns. It has roughly the consistency of peanut butter, which is the sweet spot for pushing through a fitting while still staying put once it is inside.

Go softer and some greases can squeeze out of loose joints or drip in summer heat. Go firmer and a lever gun struggles, and any grease gets harder to pump in cold weather.

Grease Thickener Types and Water Resistance Compared

For anything that touches water, choose a grease built for washout resistance, typically a calcium sulfonate or a lithium complex marine grease, over a general purpose lithium grease. The thickener is the soap structure that holds the oil, and it determines how the grease handles water, heat, and mixing with other greases.

General purpose lithium grease is fine on a lawn mower. Plain lithium grease on a winch shaft or other fitting that is dunked often can soften and wash out, while a waterproof marine grease is built to hold up in the same spot.

Water resistance varies by product within each family, so check the grease data sheet and the equipment manual.

One rule matters more than the brand. Do not mix incompatible thickeners. Some polyurea and lithium greases are incompatible, and when incompatible greases meet in the same joint the blend can soften and run out. Check both manufacturers' compatibility information. When switching greases, follow the component maker's changeover procedure. The purge or cleaning method must come from the equipment and lubricant manufacturers.

Which Size Fits Your Gun, a 14 oz Cartridge or a 3 oz Tube?

Buy 14 oz cartridges for a full size grease gun and 3 oz tubes for a mini gun or a glovebox kit. The 14 oz cartridge is the industry standard for lever and pistol grip guns, while 3 oz tubes fit compact guns and are easy to stash in a tackle box or tow vehicle.

Both sizes of Marine Grease in 14 oz cartridges or 3 oz tubes carry the same NLGI 2 waterproof formula, so you can run a big gun at home and a small one on the road without mixing thickeners.

Avoiding Air Locks After a Cartridge Change

Trapped air between the follower and the pump head can cause priming failures. Loosen the head about one turn, then pump until a bead of grease shows at the threads and retighten it. Finish by pumping into a rag until clean grease flows from the coupler.

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Marine Grease Gun

Grease trailer bearings, zerk fittings, bike gears, automotive parts, tractors, and machinery with one tool.

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Before connecting, wipe each fitting clean. Dirt on a fitting goes straight into the joint with the grease. Keep a stack of shop rags from the Better Boat sponges, cloths, and towels collection in the grease bucket for exactly that reason.

Where to Use a Grease Gun on a Boat and Trailer

A typical outboard boat and trailer has several grease fittings, and many of them call for an NLGI 2 marine grease. Confirm the grease and the interval in each owner's manual.

• Outboard swivel bracket and tilt tube. Follow the engine manual, which typically calls for pumping slowly until fresh grease just shows at the seams.
• Steering cable tube. Grease with the motor tilted down and the cable retracted, following the steering maker's instructions.
• Trailer coupler. A small amount is enough. Over greasing just collects grit.
• Winch and roller shafts. A small amount, stopping when fresh grease just appears at an open fitting.
• Wheel bearings with grease caps. Follow the bearing manufacturer, since over pumping can blow out the rear seal.

Trailer wheel bearings are a topic of their own, with the right wheel bearing grease, repacking technique, and seal checks all going well beyond what a grease gun covers, so treat them as a separate job. For the rest of the trailer, the Better Boat trailering and boat trailer accessories collection covers the hardware those fittings live on. For lower units and powerheads, see the Better Boat engine maintenance collection, since outboard service goes beyond what grease handles.

A common mistake is pumping until the joint stops taking grease. On a sealed joint or a fitting with no relief path, clean grease may never appear, and the pressure goes into the seal instead. Use the amount the equipment manual specifies there, and save the stop when fresh grease appears rule for open fittings designed to purge.

Frequently Asked Questions

Can I use marine grease in a regular grease gun?

Yes, marine grease in a standard 14 oz cartridge fits most standard lever, pistol grip, and cordless grease guns, but check the gun's manual for its cartridge size and loading system. Most marine grease is NLGI 2, the same consistency the gun is designed for, so it pumps the same as general purpose grease.

Why does my grease gun stop pushing grease after a cartridge change?

An air pocket trapped between the follower and the pump head is the usual cause. Loosen the head about one turn, pump until a bead of grease appears at the threads, then retighten and pump into a rag until grease flows steadily.

Is it okay to mix two different types of grease in the same fitting?

No, not unless both greases use compatible thickeners. Incompatible blends can soften and leak out of the joint, and compatibility depends on the specific products, not just the thickener names. When switching, follow the component maker's changeover procedure.

Is NLGI 2 grease thick enough for boat trailer wheel bearings?

NLGI 2 is commonly specified for trailer wheel bearings, but confirm the hub maker's requirement. The guide to wheel bearing grease for boat trailers covers bearing grease in detail.

How do you know when a fitting has enough grease?

Start with the owner's manual, which may give a specific amount or method. On open fittings designed to purge, stop when fresh grease just appears. On sealed joints and hubs, use less and never force grease past a seal, since extra grease attracts grit and too much pressure can push the seal out.

The Bottom Line

The best grease for a grease gun is the one matched to the job, and for boats and trailers that means waterproof, high temperature, NLGI 2. Pick the cartridge size that fits your gun, bleed the air before you start, never mix incompatible thickeners, and on fittings designed to purge, stop pumping when clean grease shows, with the equipment manual as the final word.

Better Boat Marine Grease Tube 3oz or 14oz is a good fit for exactly this reason. The 14 oz cartridges handle seasonal service in the shop, the 3 oz tubes ride in the tow vehicle, and both resist washout in wet conditions. Load a fresh cartridge before service day, check each component manual for its grease, and most common grease points on the boat and trailer are covered.

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