MERCURY 4 HP 4MH OUTBOARD MOTOR

Description

The Mercury 4 HP 4MH outboard motor is where Mercury’s small portables start to feel like proper little boat engines. You get a real forward, neutral and reverse gearbox, a pressurised oil system, shallow water drive and an option to add charging, all in a package one person can still carry. We have it for sale new, with the Mercury factory warranty, and we ship worldwide.

If you’ve been looking at the 2.5 and 3.5 and thinking “I really want reverse”, or your boat is a bit too heavy for those, this is usually the answer. Below you’ll find what the Mercury 4 HP 4MH outboard motor does well, which boats it fits, the full specs, and the honest downsides too.

On this page:

• Why buy the Mercury 4 HP 4MH outboard motor
• What 4MH means
• Boats it fits
• On the water
• Features
• Specifications
• Maintenance
• Real world setups
• Compared with nearby models
• Price and shipping
• FAQ

Why buy the Mercury 4 HP 4MH outboard motor

Three things set this motor apart from the smaller Mercurys: a gearbox with reverse, pressurised lubrication, and a bit more muscle. Each of those makes a real difference when you use the boat.

Reverse first. The 2.5 and 3.5 swing round 360 degrees to go backwards. That works, but it’s fiddly when you’re trying to back off a beach, pull away from a crowded dock or hold position against a breeze. The Mercury 4 HP 4MH outboard motor has a forward mounted shift lever with proper forward, neutral and reverse. Slip it into reverse, twist the throttle, and you go backwards. Simple, and much less stressful.

Then there’s the oil system. The smaller motors use a splash system. The 4 hp uses a pressurised wet sump with a low oil pressure warning. That’s the same basic approach used on bigger outboards, and it’s kinder to the engine over long running hours, especially at steady trolling speeds.

Finally, it’s simply a stronger motor. The single cylinder has a displacement of 123 cc, up from 85 cc on the 2.5 and 3.5. That extra size gives you more torque, which is what actually pushes a loaded boat through the water.

The trade off is weight. The Mercury 4 HP 4MH outboard motor is about 55 pounds. That’s still easy for most adults to carry a short distance, and it has an integrated handle, but it’s noticeably heavier than the 41 pound 3.5. If you’re lifting it in and out of a dinghy from a yacht every day, bear that in mind.

What “4MH” means

• 4 is the horsepower.
• M is manual start.
• H is tiller handle steering.
• No L means a 15 inch short shaft.

The long shaft version is the Mercury 4MLH, with a 20 inch shaft for sailboats and taller transoms.

Boats the Mercury 4 HP 4MH outboard motor fits

Measure from the top of the transom down to the bottom of the hull. Around 15 inches, this short shaft Mercury 4 HP 4MH outboard motor is right. Around 20 inches, go for the 4MLH.

Boats that suit it well:

• Small aluminum fishing boats and car toppers, roughly 10 to 12 feet
• Inflatables and RIBs in the 2.7 to 3.5 metre range
• Hard dinghies and tenders
• Small jon boats on calm water
• Square stern canoes built for a motor

On a light inflatable with one person, a 4 hp can sometimes get close to planing. On most aluminum boats it’s a displacement speed motor, meaning a steady cruise rather than skimming along. If you want to plane a 12 to 14 foot tinny with two people, the Mercury 8MH or 9.9MH are better picks.

Running the Mercury 4 HP 4MH outboard motor

Starting

Open the fuel vent and tap, set the choke when cold, check it’s in neutral, and pull. Start in gear protection stops it firing up in forward or reverse, so you won’t get any nasty surprises at the dock. It usually catches in a pull or two once it’s been run in.

Shifting

The shift lever is mounted at the front of the motor, where it’s easy to reach from the tiller. Forward, neutral, reverse. Move it deliberately, at idle, and it clicks cleanly into gear.

Throttle and trolling

Twist grip throttle with tension control. Set it and let go. At low speed the Mercury 4 HP 4MH outboard motor trolls nicely and idles smoothly, and the through prop hub exhaust keeps things quiet and pushes the fumes underwater.

Shallow water drive

This is a genuinely useful feature. You can lock the motor partly tilted so the prop runs higher in the water. When you’re creeping over a sand bar, a weed bed or a rocky shallow at low speed, it lets you keep going without dragging the skeg along the bottom. There are six trim positions in total, so you can also fine tune how the boat sits.

Speed

Full throttle is 4,500 to 5,500 rpm. Actual speed depends on your boat and load, so I won’t guess at a number. On a suitable boat, the motor should reach that rpm range without labouring.

Mercury 4 HP 4MH outboard motor features

• Compact and lightweight for its class
• Digital CD ignition with spark advance
• High grade marine alloy construction
• Stainless steel water pump housing
• Zinc coated water passages
• Rated for saltwater use
• Sacrificial zinc anodes
• Forward, neutral and reverse gear shift
• Forward mounted gear shift selector
• Adjustable steering tension control
• Twist grip throttle with tension control
• Integrated carry handle
• Thermostat controlled water cooling
• Shallow water drive with 6 trim positions
• Quiet through propeller hub exhaust
• 1.15 litre integral fuel tank, plus external tank connection
• Start in gear protection
• Low oil pressure warning indicator
• ESG over rev protection
• Safety lanyard stop switch
• Owner’s manual
• Mercury Marine 3 year warranty

One feature worth calling out: the external tank connection. The built in tank is handy for short trips, but the Mercury 4 HP 4MH outboard motor can also run from a separate portable tank with a fuel line. For longer fishing days, that’s the way to go. You get far more range and less topping up.

Mercury 4 HP 4MH outboard motor specifications

For the manufacturer’s overview of the range, see Mercury’s FourStroke outboards page. Model year details sometimes change slightly, so ask us if you need something confirmed on the exact unit we’ll ship.

About the optional charging kit

Out of the box, the Mercury 4 HP 4MH outboard motor doesn’t charge a battery. It doesn’t need one, since it’s pull start. But Mercury offers a small 12 volt, 50 watt charging coil that can be fitted. It won’t run a big electronics setup, but it’s enough to keep a small battery topped up for a fish finder or navigation lights on a small boat. If that’s something you want, mention it when you order and we’ll explain what’s involved.

Maintaining the Mercury 4 HP 4MH outboard motor

Fuel

Use fresh 87 octane unleaded with no more than 10% ethanol. Stale fuel is what kills small carburetors. If you’re laying the Mercury 4 HP 4MH outboard motor up for more than a few weeks, turn off the fuel and let it run until it stops. If you use an external tank, disconnect the line and run it dry the same way.

Oil

It takes about 450 ml of 10W-30. Check the dipstick before every trip. The low oil pressure warning is there to help, but it’s not a substitute for checking. Change the oil after the first 20 hours, then every 100 hours or once a season.

Gear case

Change the gear lube once a year. Milky lube means water is getting past a seal. Better to find that in the driveway than halfway across a lake.

Cooling

Watch for the telltale water stream every time you start. No stream, stop the engine and check for a blocked intake or a worn impeller. In saltwater, flush after every outing.

Transport

Carry it upright by the handle. If you must lay it down, follow the side shown in the owner’s manual. Four strokes don’t like being laid on the wrong side.

For the basics of safe small boat handling, the US Coast Guard’s boating safety site is worth ten minutes of your time, wherever in the world you boat.

Real world setups for the Mercury 4 HP 4MH outboard motor

The small lake fishing boat

A 10 or 12 foot aluminum boat, one or two people, rods, a small cooler. The Mercury 4 HP 4MH outboard motor moves this kind of boat along at a relaxed pace and trolls beautifully. Reverse makes backing off the ramp and away from snags much easier than on the smaller motors. Add an external fuel tank and you can fish all day.

The bigger tender

For a 3 to 3.5 metre inflatable or RIB, the 4 hp’s extra torque is welcome, especially with passengers and gear aboard. Reverse is handy when you come alongside a yacht in a swell. The extra weight over a 3.5 is the only real downside here.

The canal and river runabout

On slow rivers and canals, where speed limits are low anyway, a 4 hp is often all you need. It’s quiet enough not to disturb anyone, and the shallow water drive helps in the shallows along the banks.

Who should look elsewhere

If you need to carry the motor a long way, lift it on and off a yacht tender every day, or you have a very light canoe, the 55 pound weight of the Mercury 4 HP 4MH outboard motor might feel like too much. The 3.5MH could suit you better. If you want real speed on a 12 to 14 foot boat, step up to 8 or 9.9 hp.

But if you want a small motor with a proper gearbox, better lubrication and more torque, in something one person can still lift, the Mercury 4 HP 4MH outboard motor is a very good buy.

First run and break in

When the motor arrives, check it over for shipping damage. Add oil if needed and check the level on the dipstick. Clamp it to the centre of the transom, tighten both clamp screws firmly by hand and tie a safety line from the motor to the boat. Add fresh fuel, connect the lanyard to yourself, put it in neutral and start it. Let it warm up and check the cooling water telltale.

For the first couple of hours, vary your speed and avoid long periods at full throttle. After that, run it normally. Change the oil after the first 20 hours to clear out any break in residue.

Off season storage

Flush the motor with fresh water. Run it dry of fuel. Change the oil. Change the gear lube. Grease the swivel and clamp screws. Store it upright or on the correct side, in a dry place. Next season, add fresh fuel, check the oil and you’re away. It’s twenty minutes of work that saves you a spring of pulling on a cord.

Questions buyers ask before ordering the Mercury 4 HP 4MH outboard motor

“Is 4 hp enough for my 12 foot tinny?”

For one or two people fishing on a lake or a sheltered bay, yes, at a steady displacement speed. It won’t plane that boat with two adults and gear aboard. If the main goal is trolling and getting to nearby spots, the Mercury 4 HP 4MH outboard motor does the job well and costs less to run than a bigger motor. If you need to cover distance quickly, go up to 8 or 9.9 hp.

“Why is it heavier than the 3.5?”

Because it’s a different, bigger engine. The larger cylinder, the gearbox with reverse and the pressurised oil system all add weight. You’re paying about 14 pounds for a noticeably more capable motor. For many buyers that’s a very fair trade.

“How long will the built in tank last?”

At a gentle cruise it goes further than you’d guess, but it’s still only a little over a litre. For short runs it’s perfect. For a full day on the water, hook up an external tank. That’s one of the nicest things about the Mercury 4 HP 4MH outboard motor compared with the smaller models, which don’t have that option.

“Is it hard to start?”

No. With fresh fuel and the choke set correctly, a Mercury 4 HP 4MH outboard motor normally starts within a couple of pulls. Most hard starting on small motors comes back to stale fuel or a forgotten fuel tap or tank vent. Check those first before assuming anything is wrong.

“Can I leave it on the boat?”

Yes. Tilt it up out of the water when you’re not using it, especially in saltwater, and lock it to the transom if theft is a worry where you keep the boat. An outboard lock over the clamp screws is cheap and puts off casual thieves.

Fuel use and range

Like every displacement boat, the biggest fuel savings come from backing off the throttle. The last bit of throttle adds little speed and uses a lot more fuel. Run the Mercury 4 HP 4MH outboard motor at around three quarters and you’ll often find the boat is barely slower, while the motor is quieter and burns noticeably less.

For longer outings, pair it with a small external tank. A few litres of fresh fuel in a portable tank gives most small boat anglers a full day of trolling and moving between spots, with fuel to spare. Keep a spare fuel line clip and a shear pin in the boat, and you’ve covered the most common small breakdowns.

Why so many small boat owners choose Mercury

Part of it is the dealer and parts network, which is huge. Wherever you are in the world, you’re rarely far from someone who can supply a Mercury impeller, spark plug or propeller. Part of it is the reputation. Small Mercury four strokes have a name for starting reliably and running for a long time with basic care. And part of it is the design detail, things like the start in gear protection, the low oil pressure warning and the shallow water drive on the Mercury 4 HP 4MH outboard motor, which make daily use easier and safer. None of those are flashy features, but they’re the ones you notice after a few seasons.

Paperwork, warranty and keeping records

When your Mercury 4 HP 4MH outboard motor arrives, write down the serial number and keep it with your invoice. Take a photo of the serial plate on your phone too. If you ever need warranty work, a dealer will ask for both, and it makes the process much quicker. The Mercury factory warranty starts from the date of purchase, so hang on to that paperwork.

It is also worth keeping a simple log: date, engine hours if you have them, oil changes, gear lube changes, impeller replacements and anything unusual you noticed. It takes seconds after each service, and it adds real value if you ever sell the boat. Buyers pay more for an engine with a clear service history, and it helps any mechanic you work with understand the motor quickly.

Check your boat insurance as well. Many policies have specific requirements for outboard security, such as a lock on the clamps or bracket, and some ask for the serial number. Better to sort that out on day one than find out after a problem.

The Mercury 4 HP 4MH outboard motor compared with nearby models

Versus the 3.5MH: the 3.5 is about 14 pounds lighter but has no reverse gear, splash lubrication and less torque. Pick the 3.5 for light tenders and canoes. Pick the 4 for small fishing boats and heavier inflatables.

Versus the 5MH: a little more power in a similar package. If horsepower rules or budget aren’t an issue, the 5 gives you a bit more in reserve.

Versus the 6MH: noticeably stronger and still portable. Good if your boat is at the upper end of the 4 hp’s range.

Long shaft option: the 4MLH is the same motor with a 20 inch shaft.

See the full range in the Mercury 4 HP outboard motors section and our main Mercury outboard motors for sale category.

Mercury 4 HP 4MH outboard motor for sale: price and worldwide shipping

The price of the Mercury 4 HP 4MH outboard motor is shown at the top of this page. Add it to your cart to buy, or message us for a delivered price to your country.

In the box

• Mercury 4 HP 4MH outboard motor, new
• 3 blade aluminum propeller, fitted
• Built in fuel tank with external tank connection
• Owner’s manual
• Mercury Marine 3 year factory warranty from the date of purchase

Shipping

We ship worldwide. The motor is securely packed, shipped dry, and sent by courier or freight with full tracking. Duties and local taxes vary by country, and we’ll talk you through them before you buy if you like.

Buyer information

Please read our refund and return policy, check our customer reviews, and learn more about us on the about page.

Mercury 4 HP 4MH outboard motor FAQ

Does the Mercury 4 HP 4MH outboard motor have reverse?

Yes. It has a full forward, neutral and reverse gearbox with a front mounted shift lever.

How much does it weigh?

About 55 pounds.

Can I use an external fuel tank?

Yes. It has a built in tank and a standard external tank connection.

Will it charge a battery?

Not as standard. An optional 12V 50W charging coil can be fitted.

Is it good in saltwater?

Yes, it’s saltwater rated. Flush it after each use.

Is it new?

Yes. New, with the full Mercury factory warranty.

Do you ship to my country?

We ship worldwide. Contact us with your location for a delivered quote.

Get your Mercury 4 HP 4MH outboard motor

A small motor with a proper gearbox, better lubrication and enough torque for a real little fishing boat. That’s the Mercury 4 HP 4MH outboard motor. Add it to your cart now, or ask us a question first. You can also look through all our outboard motors for sale.