MERCURY 3.5 HP 3.5MH OUTBOARD MOTOR

Description

If you want a motor you can carry in one hand but you’ve found a 2.5 a little short on shove, the Mercury 3.5 HP 3.5MH outboard motor is where most people land. Same light, simple package, a bigger carburetor, and noticeably more pull when the boat is loaded or the wind picks up. We sell it new, with Mercury’s factory warranty, and we ship it worldwide.

I’ll be straight with you about what this motor is good at and what it isn’t. It’s a tender and small boat motor. It’s not going to plane a fishing boat. But for inflatables, canoes, prams and small dinghies, it’s about as good as small outboards get.

On this page:

• Why choose the Mercury 3.5 HP 3.5MH outboard motor
• What the model code means
• Boats it suits
• Using it on the water
• Features
• Specifications
• Maintenance
• How it compares
• Price and shipping
• FAQ

Why choose the Mercury 3.5 HP 3.5MH outboard motor

The short answer is that it gives you a real step up in usable power without adding any weight worth talking about. The Mercury 3.5 HP 3.5MH outboard motor shares its basic body with the 2.5, so it’s around 41 pounds with an integrated carry handle that balances nicely when you lift it. What’s different is inside: Mercury fitted a larger carburetor, and that extra breathing turns into better acceleration and more thrust at the top end.

You feel the difference most in three situations. Pushing a heavier inflatable with two people aboard. Running against a tidal current or a river flow. And heading back to the boat or the ramp into a stiff breeze. A 2.5 will get there. The 3.5 gets there with less drama.

It’s a four stroke, single cylinder engine. That means no mixing oil into fuel, a quiet exhaust that exits below the waterline, and none of the oily smell that old two strokes leave on your hands and clothes. The fuel tank is built in, holding just under a litre, so there’s nothing extra to carry.

Who buys the Mercury 3.5 HP 3.5MH outboard motor from us? Mostly yacht owners who need a dependable tender motor, canoe and small boat anglers, and people with a small pram or dinghy at a lake house. We also sell a fair few to people replacing a tired old 2 or 3 hp two stroke that finally gave up.

What “3.5MH” means

• 3.5 is the horsepower.
• M means manual (pull) start.
• H means tiller handle steering.
• No L in the code means a 15 inch short shaft.

If you see 3.5MLH, that’s the same motor with a 20 inch long shaft. The L is the only difference, but it’s an important one, so read the next section before you pick.

What boats the Mercury 3.5 HP 3.5MH outboard motor suits

Get a tape measure. Measure from the top of the transom, where the motor clamps, straight down to the bottom of the hull. Around 15 inches means the short shaft Mercury 3.5 HP 3.5MH outboard motor is right. Around 20 inches means you want the long shaft.

Typical short shaft boats for this motor:

• Inflatable tenders and dinghies, roughly 2.3 to 3.2 metres
• Hard dinghies and prams with a low transom
• Square stern canoes and canoes on a side mount
• Small car topper aluminum boats on sheltered water

Boats that usually want the long shaft instead are sailboats with a transom bracket, some taller dinghies, and small craft where the transom sits higher above the water.

Be realistic about load and speed. The Mercury 3.5 HP 3.5MH outboard motor will move a small boat along nicely at displacement speed, and it’ll get a light inflatable with one person close to planing in some cases. It will not plane a typical 12 to 14 foot aluminum fishing boat with gear. For that, look at the Mercury 6MH, the 8MH or the 9.9MH.

Using the Mercury 3.5 HP 3.5MH outboard motor on the water

Starting it

Open the vent on the fuel cap, turn the fuel tap on, pull the choke when cold and give it a steady, firm pull. Once it’s warm, it should start on the first or second pull. Push the choke back in once it’s running evenly.

No reverse gear, and why that’s fine

Like the 2.5, the Mercury 3.5 HP 3.5MH outboard motor has forward and neutral only. To go backwards you swing the whole motor round on its 360 degree swivel so the prop pushes the other way. It sounds strange, but it’s quick and actually gives you excellent control when you’re easing up to a yacht’s swim platform or a crowded dinghy dock. There’s a tension adjuster so the steering isn’t sloppy.

Throttle and trolling

The twist grip throttle has a friction knob. Tighten it a bit and the motor holds its speed when you let go. Trolling speed is easy to find and the motor idles smoothly thanks to the thermostat controlled cooling, which keeps the engine warm enough to run cleanly even in cold water.

Noise

It’s quiet. The exhaust exits below the water and the four stroke engine runs smoothly. You can have a conversation in the boat without shouting, which matters more than people think if you’re out early and don’t want to annoy the whole anchorage.

Speed and range

Speed depends heavily on the boat and the load, so I’d rather not give a number that won’t match your setup. Full throttle sits at 5,000 to 6,000 rpm. Fuel use at moderate throttle is very low. For long days, bring a small spare can of fresh fuel.

Mercury 3.5 HP 3.5MH outboard motor features

• Compact and lightweight
• Larger carburetor for more performance than others in the class
• Digital CD ignition
• High grade marine alloy construction
• Stainless steel water pump housing
• Zinc coated water passages
• Rated for saltwater use
• Sacrificial zinc anodes
• Forward and neutral gear shift
• 360 degree steering with tension feature
• Twist grip throttle with tension control
• Integrated, balanced carry handle
• Thermostat controlled water cooling
• Visual oil level indicator
• Over rev protection
• 4 trim positions
• Below the water exhaust
• 1.0 litre integral fuel tank
• Safety lanyard stop switch
• Owner’s manual
• Mercury Marine 3 year warranty

The over rev protection is worth mentioning on a tender motor. In a chop, a small inflatable can bounce the prop out of the water. Without protection, the engine would scream. The Mercury 3.5 HP 3.5MH outboard motor limits that, which is kinder to the engine over the years.

Mercury 3.5 HP 3.5MH outboard motor specifications

For Mercury’s own overview of the small portable range, see their FourStroke outboards page. If a particular detail is important to your purchase, ask us and we’ll check it against the exact unit.

Maintaining the Mercury 3.5 HP 3.5MH outboard motor

Small outboards are simple to look after. Most of the problems we hear about come from one or two bad habits, so here’s what actually matters.

Fresh fuel, every time

The carburetor jets on a motor this size are tiny. Old fuel leaves varnish that blocks them, and then the motor won’t idle or won’t start. Use fresh 87 octane with no more than 10% ethanol. If you’re not going to use the Mercury 3.5 HP 3.5MH outboard motor for a few weeks, turn off the fuel tap and let it run until it dies. That keeps the carb clean.

Oil

About 300 ml of 10W-30 four stroke oil. Check the level window before every outing. First change at 20 hours, then yearly or every 100 hours.

Transporting it

Carry it upright by the handle. If you need to lay it down in a car or on a boat, follow the owner’s manual for which side goes down. The wrong side lets oil into places it shouldn’t be.

Saltwater

As a tender motor it’ll see a lot of salt. Flush it in fresh water whenever you get the chance. Check the zinc anode and replace it when it’s about half gone.

Gear oil

Change the lower unit oil once a year. If it’s milky when it comes out, a seal is letting water in. Catch that early and it’s a cheap fix.

New to small boats? The US Coast Guard boating safety resources are a good place to start. The advice on kill switches, life jackets and fuel handling applies wherever you boat.

A few real world uses we hear about

One customer runs a Mercury 3.5 HP 3.5MH outboard motor on a hard dinghy from a mooring in a busy harbour. He picked the 3.5 over the 2.5 because the harbour has a strong tidal stream and he got tired of crabbing sideways across it. Another uses one on a square stern canoe on a river, where the extra thrust helps against the current on the way back upstream. We also sell them to dive and snorkel groups who run small inflatables from a bigger boat, because they’re light enough to pass down without a crane.

The pattern is the same. People want the lightness of a 2.5, but they need a little more push. That’s exactly the gap this motor fills.

Setting it up the first time

Centre the Mercury 3.5 HP 3.5MH outboard motor on the transom and tighten the clamp screws firmly by hand. Tie a safety line from the motor to the boat. Adjust the tilt pin so the motor sits upright in the water with the boat loaded as you normally use it. Fill the oil if needed (check the window), add fresh fuel, attach the stop switch lanyard to yourself and start it in neutral. Let it warm up for a minute and look for the cooling water stream coming out of the telltale. Then off you go.

For the first couple of hours, vary the throttle rather than holding full speed. After that, just use it normally.

Storing it between seasons

Flush it, run the carb dry, drain the tank, change the oil, grease the swivel and clamp screws and store it upright or on the correct side in a dry place. That’s all. In spring, fill it with fresh fuel, check the oil, and it should start as if it had never been away.

Things people ask us before buying the Mercury 3.5 HP 3.5MH outboard motor

“Is the jump from 2.5 to 3.5 really noticeable?”

Yes, more than the numbers suggest. On paper it’s one extra horsepower. On the water, the bigger carburetor means the Mercury 3.5 HP 3.5MH outboard motor picks up quicker from idle and holds its speed better when the boat is heavy. If you’ve ever sat at full throttle on a 2.5 watching the shore creep past, you’ll appreciate it. If your boat is very light and your trips are short and calm, the difference matters less.

“Will it push my inflatable with two adults?”

For most tenders around 2.5 to 3 metres, yes, at a sensible displacement speed. Don’t expect it to jump onto the plane with two people and a bag of shopping. If planing is the goal, you need more like 6 hp or above, and your inflatable needs to be rated for it.

“Can I leave it on the transom all season?”

You can, and plenty of people do, especially on a tender that lives in the water. Tilt it up when you’re not using it so the lower unit isn’t sitting in the water growing weed and barnacles. Lock it to the boat if theft is a concern where you keep it. Small outboards are easy to walk off with, which is exactly why they’re so handy for you, and unfortunately handy for thieves too.

“Do I need a separate fuel tank?”

No. The Mercury 3.5 HP 3.5MH outboard motor has an integral tank of just under a litre. For longer trips, carry fresh fuel in an approved container and top up when needed. Always refuel with the engine off and away from any heat.

“What about the prop?”

It comes with a 3 blade composite propeller that suits most tenders and small boats. Composite props are light and cheap to replace if you hit something. It’s worth carrying a spare shear pin and the small tools to change it if you run in shallow or rocky water.

“Is it easy to service myself?”

Very. Oil changes, gear lube, spark plug and anode are all jobs a handy owner can do with basic tools and the owner’s manual. That’s one of the reasons small Mercurys are so popular with cruisers who spend long periods away from a dealer.

Why a four stroke instead of an old two stroke

We still get asked this, usually by someone with a much loved old two stroke that’s finally tired. Here’s the honest comparison. A two stroke of this size is lighter by a few pounds and very simple, but it needs oil mixed into every tank of fuel, it smokes, it smells, and it’s thirstier. In many places they’re no longer sold new because of emission rules.

The Mercury 3.5 HP 3.5MH outboard motor runs on straight unleaded. It’s quieter, cleaner, uses less fuel and idles more smoothly, which makes it far nicer for trolling or creeping around an anchorage. For most people, those everyday improvements are worth far more than a few pounds of extra weight.

Fuel use and how far you’ll get on a tank

This is one of the questions I can only answer roughly, because it depends on how hard you run it, how heavy the boat is and the conditions. What I can tell you is that the Mercury 3.5 HP 3.5MH outboard motor is frugal. At a relaxed cruising throttle it burns very little, and many tender owners go several trips to shore and back before they need to top up the built in tank.

Running flat out burns fuel much faster for only a small gain in speed, which is true of almost every small displacement boat. Back the throttle off a touch from full and you’ll often lose very little speed while using noticeably less fuel. It’s quieter too.

For a longer day out, carry a small approved fuel can with fresh unleaded, and a funnel. Top up on land or with the motor stopped and cooled. Close the tank vent when you’re finished, so the fuel doesn’t pick up moisture or leak when the motor is tilted or carried.

One more tip. If you only use your Mercury 3.5 HP 3.5MH outboard motor now and then, buy fuel in small amounts. A big can that sits for months turns stale, and stale fuel is the enemy of every small carburetor. Buy little, buy often, and your motor will start first pull for years.

How the Mercury 3.5 HP 3.5MH outboard motor compares

Versus the 2.5MH: same weight and size, less power, slightly cheaper. If your boat is tiny and you only use it on calm water, the 2.5 is fine. Otherwise the 3.5 is the better all rounder.

Versus the 4MH: the 4 is heavier at around 55 lb, but it has a real forward, neutral and reverse gearbox, a pressurised oil system and an optional charging coil. It suits small fishing boats better. The Mercury 3.5 HP 3.5MH outboard motor is lighter and handier as a tender motor.

Versus the 5MH and 6MH: more power and gears, but more weight too. Good if you’ve outgrown a tender and want something for a small fishing boat.

You can browse every size in our Mercury outboard motors category, or go straight to the Mercury 4 HP and 6 HP sections.

Mercury 3.5 HP 3.5MH outboard motor for sale: price and worldwide shipping

The current price of the Mercury 3.5 HP 3.5MH outboard motor is shown at the top of this page. You can buy it straight away through the cart, or contact us for a delivered price to your country before you commit.

What you get

• Mercury 3.5 HP 3.5MH outboard motor, new
• Fitted 3 blade composite propeller
• Built in fuel tank
• Owner’s manual
• Mercury Marine 3 year factory warranty from the date of purchase

Shipping worldwide

We ship to buyers all over the world. The motor is boxed securely and sent by courier or freight, with tracking. It ships dry, without fuel, as carriers require. Import duty and local taxes vary by country, and we’ll happily explain what to expect before you pay.

Peace of mind

Read our refund and return policy, see what other buyers have said on our reviews page, and find out more about us on the about page.

Mercury 3.5 HP 3.5MH outboard motor FAQ

Is the Mercury 3.5 HP 3.5MH outboard motor new?

Yes. It’s brand new with the full Mercury factory warranty.

Does it have reverse?

No reverse gear. You rotate the motor 180 degrees on its swivel to go backwards.

How much does it weigh?

About 41 pounds, with a balanced carry handle.

Is it good in saltwater?

Yes, it’s saltwater rated. Flush it with fresh water after use.

Can it charge a battery?

No. The 3.5 has no charging option. Step up to the 4 hp or bigger if you need that.

Short shaft or long shaft?

Measure your transom. About 15 inches, choose this 3.5MH. About 20 inches, choose the 3.5MLH.

Do you ship to my country?

We ship worldwide. Tell us where you are through the contact page for a delivered quote.

Order your Mercury 3.5 HP 3.5MH outboard motor

Light enough to carry, strong enough to push through wind and current, and simple enough to look after yourself. That’s the Mercury 3.5 HP 3.5MH outboard motor. Add it to your cart now, or ask us a question first. You can also compare it against the rest of our outboard motors for sale.