MERCURY 300HP L FOUR STROKE OUTBOARD MOTOR DTS FOR SALE

Description

The Mercury 300HP L Four Stroke DTS is a 300 HP Mercury outboard with a 20-inch shaft, Digital Throttle and Shift (DTS) controls and a black finish. It suits center consoles, bay boats, pontoons and offshore boats.

What the 300L Model Code Means

• L: L = 20-inch shaft
• DTS: Digital Throttle and Shift

Key Features of the Mercury 300HP L Four Stroke DTS

Mercury’s V8 FourStroke 300 uses a 4.6-litre V8, the largest displacement in its class, for strong low and mid-range torque. Mercury quotes a dry weight from about 527 lb for the lightest version, a full-throttle range of 5,200 to 6,000 rpm and an 85-amp alternator with Idle Charge, which raises idle speed when battery voltage is low.

Digital Throttle and Shift

DTS replaces mechanical cables with electronic signals for smooth, precise shifting and easy engine synchronisation. It needs Mercury DTS controls and SmartCraft wiring. Our twin outboard set-up guide covers rigging two engines.

Who the Mercury 300HP L Four Stroke DTS Suits

At 300 HP, this engine is aimed at center consoles, bay boats, pontoons and offshore boats. Check that your hull is rated for the power and weight, and decide early whether you want a single or twin installation. Our guide on whether a high-horsepower outboard is worth it and our offshore outboard buying guide can help you size the power correctly.

Why Choose a Mercury 300 HP Outboard

Mercury’s large four-strokes use SmartCraft digital diagnostics, so a technician can read engine hours, fault codes and running history quickly. That makes servicing easier wherever you keep the boat and gives you a clear record of how the engine has been used. On bigger boats twin installations are common: pairing a standard and a counter-rotating engine gives straighter tracking, redundancy far offshore and stronger acceleration with a heavy load. Mercury also has a wide dealer and parts network, which matters when you need filters, anodes or a propeller at short notice.

Mercury 300HP L Four Stroke DTS Specifications

• Output: 300 HP
• Engine: 4.6-litre 64-degree V8, DOHC 32-valve
• Shaft length: 20 in
• Rotation: standard
• Controls: Digital Throttle and Shift (DTS)
• Colour: black
• Full-throttle range: 5,200 to 6,000 rpm
• Alternator: 85 A with Idle Charge

Rigging and Running the Mercury 300HP L Four Stroke DTS

Engines of this size need Mercury-compatible controls, SmartCraft gauges, a heavy-duty marine battery and a propeller matched to your hull. If you are replacing an older engine, read our guide to repower costs before you budget.

Regular servicing keeps any Mercury reliable. Follow our outboard maintenance checklist, change the lower unit oil on schedule and winterize the engine if it will sit unused for months. Official specifications are on Mercury Marine’s website.

Before You Buy the Mercury 300HP L Four Stroke DTS

• Measure your transom to confirm the shaft length.
• Check your boat’s capacity plate allows 300 HP and the engine weight.
• Choose a propeller with our propeller buying guide, and follow the break-in steps for a new outboard.

How the Mercury 300HP L Four Stroke DTS Performs on the Water

The Mercury 300HP L Four Stroke DTS belongs to the high-horsepower class used on offshore center consoles, walkarounds and twin- or triple-engine rigs. At 300 HP per engine it is designed to accelerate a heavy, fully fuelled boat onto the plane quickly and to hold a fast cruise in open water. Smooth power delivery, strong charging output for electronics, and dependable cooling at sustained high load are what count in this class, more than the top-speed figure.

Performance on your boat will depend on hull type, load, trim and propeller. That is why we always suggest matching the propeller to the boat rather than relying on the one fitted at the factory.

Is 300 HP the Right Size for Your Boat?

Start with the capacity plate fixed near the helm or transom of your boat. It states the maximum horsepower and the maximum engine weight the hull is rated for, and you should never exceed either. Within that limit, an engine close to the rated maximum usually gives the best all-round performance, while a smaller engine saves weight and money but may struggle with a full load. Think about your typical load too: the number of people, fuel, water, fishing or diving gear can easily add several hundred pounds.

At this power level many boats run twin engines. Twins give redundancy far from shore and better low-speed handling, while a single larger engine is lighter and cheaper to buy and maintain. If you plan a twin installation, pair standard- and counter-rotating engines so the boat tracks straight; our twin outboard set-up guide explains the details.

Choosing a Propeller for the Mercury 300HP L Four Stroke DTS

The propeller is the single biggest factor in how the Mercury 300HP L Four Stroke DTS performs on your boat. The goal is for the engine to reach the top of its rated full-throttle rpm range with a normal load. If it over-revs, fit a propeller with more pitch; if it cannot reach the range, reduce the pitch. As a rule of thumb, each inch of pitch changes full-throttle engine speed by roughly 150 to 200 rpm.

• Aluminium propellers are affordable and a good choice for shallow or debris-filled water, where a strike is likely.
• Stainless steel propellers cost more but flex less, keep their shape and often improve hole shot and top speed.
• Rotation: Standard-rotation engines use a right-hand propeller; check the rotation marking before you buy a spare.

Keep a spare propeller and the fitting kit on board. For a fuller explanation of pitch, diameter and blade count, read our propeller buying guide.

Installing and Mounting the Mercury 300HP L Four Stroke DTS

Remote-control models like the Mercury 300HP L Four Stroke DTS need controls, a steering system, a fuel system, gauges and a correctly sized battery cable. Many owners have a qualified marine technician rig the boat, because control cable adjustment, steering set-up and wiring all affect safety and reliability.

Mounting height matters on every outboard. As a starting point, the anti-ventilation plate above the propeller should sit roughly level with the bottom of the hull. Set too low, the gearcase creates drag and spray; set too high, the propeller can ventilate and lose grip in turns. The 20-inch shaft on this model must match your transom height, measured from the top of the transom down to the bottom of the hull on the centreline. Our long shaft vs short shaft guide shows how to measure correctly.

Break-In and the First Hours

A new engine needs a careful break-in so the piston rings, bearings and gears bed in properly. The owner’s manual for the Mercury 300HP L Four Stroke DTS gives Mercury’s exact break-in procedure, and it is worth following to the letter. In general, most makers ask you to vary engine speed, avoid long periods at one rpm and avoid sustained full throttle for roughly the first ten hours. Many also recommend an early first service to change the engine oil and gear oil and check for leaks. Our outboard break-in guide walks through the process step by step.

Fuel, Oil and Everyday Running

Use fresh, good-quality petrol of the octane listed in the owner’s manual for the Mercury 300HP L Four Stroke DTS. Petrol that contains ethanol absorbs water and goes stale over time, so add a marine fuel stabiliser if the boat will sit for more than a few weeks, and fit a water-separating fuel filter on boats with a built-in tank. Four-stroke engines like this one do not need oil mixed into the fuel, but you should check the engine oil level regularly and use the oil grade the manufacturer specifies.

Before each trip, check the fuel level and connections, make sure the kill-switch lanyard is attached, and confirm a strong stream of cooling water from the tell-tale outlet once the engine starts. After the trip, especially in salt water, flush the engine with fresh water and rinse the outside to slow corrosion.

Maintenance Schedule for the Mercury 300HP L Four Stroke DTS

Regular maintenance is the best way to keep the Mercury 300HP L Four Stroke DTS reliable for many seasons. The exact intervals for your engine are in the Mercury owner’s manual; the table below shows the kind of schedule most four-stroke outboards follow.

• After every use: flush with fresh water, check for fuel or oil leaks and inspect the propeller.
• First service (often around 20 hours): change the engine oil and gear oil, and check bolts and connections.
• Every 100 hours or once a year: engine oil and filter, gearcase oil, spark plugs, fuel filters, anodes and greasing points.
• Every two to three years: replace the water pump impeller, or sooner if you run in sandy or silty water.
• Larger engines: also check the timing belt or chain, thermostats and power trim fluid at the intervals the manual gives.

Keep a simple log of hours and services; it helps you plan work and supports resale value. See our Mercury outboard maintenance guide and our guide to lower unit oil for more detail.

Storage and Winterizing

If the Mercury 300HP L Four Stroke DTS will sit unused for more than a month or two, prepare it properly. Stabilise the fuel and run the engine so treated fuel reaches the injectors or carburettor, change the engine oil so acidic old oil does not sit in the engine, change the gear oil and check it for water, fog the cylinders if the manual recommends it, and grease the fittings. Leave the engine trimmed down so water drains from the gearcase and cooling passages. Remove or maintain the battery. Our Mercury winterizing guide lists each step.

Troubleshooting Common Issues

Most problems on a well-maintained outboard have simple causes. Check these first before booking a technician:

• Hard starting: stale or contaminated fuel, a blocked fuel filter, a loose kill-switch lanyard, a weak battery or a pinched fuel line.
• No water from the tell-tale: stop the engine and check for a blocked outlet, weed on the water intake or a worn water pump impeller.
• Vibration: a damaged or fouled propeller, or debris wrapped round the propeller shaft.
• Loss of power: fuel restriction, a fouled spark plug, the wrong propeller or too much load. On electronic engines, warning lights or gauge alerts point to the fault.
• Ventilation in turns: mounting height or trim may need adjusting.

If a warning alarm sounds, reduce throttle, stop when it is safe and investigate before running again. Persistent faults should be checked by a qualified technician.

How the Mercury 300HP L Four Stroke DTS Compares With Other Options

As a remote-control engine, the Mercury 300HP L Four Stroke DTS suits boats with a console. If you have a small open boat with no console, a tiller version of a similar engine can save rigging cost and weight.

Shaft length is the other key choice. This model has a 20-inch shaft; other versions of the same engine are available in different lengths to suit lower or higher transoms. For twin installations, a counter-rotating version of the same engine is usually paired with this one. Across brands, Mercury competes closely with the other leading outboard makers on reliability, fuel economy and service support, so the best choice often comes down to dealer access where you boat, controls and gauges already on the boat, and the specific features you value. Our outboard brands comparison sets out the main differences.

Getting the Best Fuel Economy From the Mercury 300HP L Four Stroke DTS

Fuel is one of the biggest running costs of any boat, and a few habits make a real difference. First, trim the engine so the bow lifts slightly and the boat runs on the flattest part of the hull; too much trim makes the propeller ventilate, too little pushes the bow into the water. Second, find the boat’s most efficient cruising speed, usually just above the point where it planes cleanly, rather than running near full throttle. Third, spread the load evenly and avoid carrying weight you do not need, such as full water tanks or unused gear.

A clean hull and a propeller in good condition also save fuel: marine growth, dents and bent blades all increase drag. Many engines in this class can display fuel flow on a digital gauge, which makes it easy to find the most economical rpm for your boat with the Mercury 300HP L Four Stroke DTS fitted. Our guides to outboard fuel efficiency and four-stroke outboards go into more detail.

Controls, Gauges and Electronics

A remote-control engine like the Mercury 300HP L Four Stroke DTS connects to a binnacle or panel control at the helm, plus gauges that show engine speed, trim, temperature, fuel and alerts. Modern engines often send this data over a digital network, so a compatible multifunction display can show it alongside your chartplotter and sonar. Use correctly sized battery cables, a battery switch and good-quality marine connectors, and route wiring away from fuel lines and moving parts.

Whatever the set-up, test the kill switch and the neutral-start safety feature regularly. If the engine will start in gear or the lanyard does not stop it, have it repaired before you go out.

Safety Equipment and Good Habits

A reliable engine is only part of safe boating. Before every trip with the Mercury 300HP L Four Stroke DTS, check the weather and tell someone where you are going and when you expect to return. Carry the safety equipment your local rules require, which usually includes lifejackets for everyone on board, a fire extinguisher, a sound signal, navigation lights and a way to call for help such as a VHF radio. A paddle or a small auxiliary engine, a spare propeller, spare fuel, a basic tool kit, a spare kill-switch lanyard, plugs and a fuel filter can turn a breakdown into a short delay.

Always wear the kill-switch lanyard while the engine is running, keep people well clear of the propeller when anyone is in the water, and never run the engine in an enclosed space because exhaust gases are dangerous.

Long-Term Ownership and Resale Value

Outboards from the major brands hold their value well when they are cared for. To get the most from the Mercury 300HP L Four Stroke DTS over its life, keep every service receipt in one place, use genuine or manufacturer-approved parts and oils, and record engine hours at each service. Fit a cover when the boat is stored, keep the anodes in good condition, and touch up chipped paint on the gearcase before corrosion starts. A well-documented engine is easier to sell, and buyers will pay more for one with a clear history.

If you ever upgrade, a clean, well-maintained Mercury 300HP L Four Stroke DTS is also a strong candidate for trade or private sale. Our guide on buying used outboard motors explains what buyers look for, which is useful to know as an owner too.

Typical Uses for the Mercury 300HP L Four Stroke DTS

Owners choose the Mercury 300HP L Four Stroke DTS for a wide range of jobs. Some of the most common are:

• Offshore fishing trips far from shore
• Fast cruising between islands or along the coast
• Twin and triple installations on large center consoles
• Commercial, charter and patrol work that demands sustained high power

Whatever you use it for, the same basics apply: match the engine to the boat’s rating, choose the right propeller, keep up with servicing and treat the fuel well. Do that, and the Mercury 300HP L Four Stroke DTS should give you dependable, economical running season after season. If you are unsure whether it suits your plans, tell us about your boat and how you use it, and we will help you decide.

First-Trip Checklist for the Mercury 300HP L Four Stroke DTS

Before you take the Mercury 300HP L Four Stroke DTS out for the first time, run through a simple checklist. It takes a few minutes and catches most of the problems that spoil a first outing.

• Confirm the engine is securely mounted and the mounting bolts or clamp screws are tight.
• Check the engine oil level and the gearcase oil, as the engine may have been shipped with minimal oil; follow the owner’s manual.
• Check that the fuel line, primer bulb and connectors are secure and that there are no leaks.
• Make sure the propeller is the right one for your boat, correctly fitted and secured with its nut and cotter pin or locking tab.
• Test the kill-switch lanyard, the neutral-start safety and the steering from lock to lock.
• Run the engine in the water and confirm a steady stream from the cooling-water tell-tale before you leave the dock.
• Keep the first outing short and close to shore, and follow the break-in instructions.

Any issue that appears on the first trip is far easier to sort out close to home. If you have questions at any stage, contact us and we will help.

Ordering and Delivery

Delivery times and costs depend on your location and the shipping method; the details are on our shipping policy page. When the Mercury 300HP L Four Stroke DTS arrives, inspect the crate or packaging before signing, note any visible damage on the delivery receipt and take photos. Check the model code on the engine’s identification plate against your order, and keep all paperwork, as you will need it for registration and future service. If you have any questions about what is included, such as a propeller, controls or a fuel tank, contact us before you order.

Frequently Asked Questions About the Mercury 300HP L Four Stroke DTS

What boats is the Mercury 300HP L Four Stroke DTS suited to?

It is best suited to offshore center consoles, walkarounds and multi-engine rigs, within the limits on your boat’s capacity plate.

Can I use it in salt water?

Yes. Like other modern marine outboards, the Mercury 300HP L Four Stroke DTS is designed for both fresh and salt water. After saltwater use, flush the engine with fresh water and check the anodes regularly.

What fuel does it use?

It runs on unleaded petrol of the octane given in the owner’s manual. As a four-stroke, it needs no oil mixed into the fuel.

How often does it need servicing?

Most four-stroke outboards need a first service after their break-in hours and then a full service every 100 hours or once a year, whichever comes first. Check the Mercury owner’s manual for the exact schedule.

How do I choose the shaft length?

Measure from the top of the transom to the bottom of the hull on the centreline. About 15 inches suits a short shaft, 20 inches a long shaft, 25 inches an extra-long shaft and 30 inches an ultra-long shaft.

How long will it last?

With regular servicing, correct storage and sensible use, a modern four-stroke outboard can give many years of reliable service. Engine hours, maintenance history and how hard it has been run matter more than age alone.

Can I fit it myself?

Remote-control engines involve controls, steering, fuel and electrical work, so we recommend a qualified marine technician for the installation.

Is a propeller included?

Supply varies by model and listing. Please contact us before ordering and we will confirm exactly what comes with the engine.

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The current Mercury 300HP L Four Stroke DTS price is shown on this page. Check our shipping policy and returns policy, compare the full Mercury 300 HP outboards, or contact us with any fit or rigging questions.