Repair & maintenance guides

Boat Fuel Additives Explained: What Stabilizers, Ethanol Treatments and Boosters Really Do

The marine store shelf is full of bottles that promise to fix fuel problems. Learn what stabilizers, ethanol treatments, water removers, octane and cetane boosters, cleaners and diesel biocides actually do, what no additive can do, how to dose them by the label and why you should not stack several products in one tank.

Boating on High-Altitude Lakes: Power Loss, Prop Changes, Cold Water and Mountain Weather

Engines lose roughly 3% of their power for every 1,000 feet of elevation, so a boat that flew at sea level can struggle on a mountain lake. Learn what's normal, when a lower-pitch prop or a dealer adjustment helps, and how to handle the strong sun, cold water and fast-changing weather up high.

Closed-Cooled Gas Engines: Why the Exhaust Elbows Still Need Checking

Closed (freshwater) cooling protects the block, but on gas sterndrives and inboards the exhaust elbows or risers, and on some systems the manifolds, are still cooled by raw water. Learn which parts still see salt or lake water, the warning signs, what the engine makers and BoatUS say about intervals, and how to inspect and look after them.

Damaged Propeller: Repair It or Replace It?

Decide whether a bent, chipped or spun prop is worth sending to a prop shop or should be replaced, what a shop can actually fix on aluminum and stainless props, and how to keep the boat running the same afterward.

Engine and Gearbox Oil Analysis: How to Take a Clean Sample and Read the Report

A lab oil analysis is like a blood test for your engine, transmission or lower unit. Learn how to pull a clean sample, what the lab measures, what wear metals, coolant, sea water and fuel in the oil can mean, and why the trend over several samples matters more than any one number.

Ethanol (E10) Fuel Care: Stabilizer, Phase Separation, Fuel Lines and Tank Vents

Keep E10 gasoline from damaging your boat engine. Learn how to use stabilizer, test for water and phase separation, and inspect the fuel lines, primer bulb, anti-siphon valve and tank vent. Most fuel-related breakdowns start with one of these.

Fishing Line Behind the Prop: How It Ruins Gearcase Seals and How to Catch It Early

Fishing line that wraps behind your propeller can melt into a sharp ring that cuts the prop shaft seals and lets water into the gearcase. Learn the quick after-trip check, how to pull the prop and clear line safely, the signs that a seal is already damaged, and when to get a pressure test.

Generator Pre-Trip Check: What to Inspect and Test Before a Cruise

A marine generator that quits on the first hot night of a cruise usually gave warning signs at the dock. Use this pre-departure checklist, based on generator makers' own advice, to inspect the oil, coolant, belt, raw-water side, exhaust and CO alarms, run the set under real load, and pack the right spares.

Gyro Stabilizer Care: Owner Checks for Seakeeper and Other Boat Gyros

A gyro stabilizer needs little from you, but what it needs matters. Learn how to start and shut it down correctly, keep its seawater cooling and zinc in shape, rinse it, read its hours and alarms, winterize it, and know which jobs belong to a certified dealer.

How to Break In a New or Rebuilt Boat Engine

The first hours on a new or rebuilt engine decide how well its piston rings seat and how long it lasts. Learn how to follow your maker's hour and RPM schedule, why you should keep changing the throttle, what to avoid (constant RPM, early full throttle, long idling), what to check every trip and when to do the first oil change.

How to Change Lower Unit (Gearcase) and Sterndrive Oil

Drain and refill the gear oil in your outboard lower unit or sterndrive, and learn to spot water intrusion before it destroys the gears. It is a 30-minute job that protects a gearcase costing thousands to replace.

How to Check and Change Coolant in a Closed Cooling System

Check, test and change the coolant in a freshwater-cooled (closed cooling) inboard, sterndrive or diesel, and learn the heat exchanger basics that keep it working. Old coolant quietly eats hoses, pumps and engine passages, and many boats go a decade without a change.

How to Find Your Engine's Serial Number, Model and Year (and Get the Official Manual)

Find the ID label on your outboard, sterndrive, inboard diesel or PWC, read the model and serial number correctly, tell it apart from the boat's HIN, and use it to open the free official owner's manual. It's the first step for ordering the right parts and following the right maintenance plan.

How to Flush an Engine While the Boat Stays in the Water

Boats kept in a saltwater slip, on a mooring or on a lift can't always use flush muffs. Learn how built-in outboard flush ports, sterndrive and inboard flush kits and flush-valve seacocks work, which engines can use them in the water, how to avoid back-flow and hydrolock, and a simple after-every-trip routine.

How to Flush Your Engine With Fresh Water

Rinse salt, silt and sand out of your outboard or sterndrive cooling system using the built-in flush port, flush muffs or a flush bag. Flushing after every saltwater trip is one of the easiest ways to prevent corrosion and overheating.

How to Get Better Fuel Economy From Your Boat

Boat fuel is expensive, but most owners can stretch every gallon further without buying anything. Learn how to find your boat's most efficient cruise RPM, why a clean bottom, the right prop, good trim and less weight matter most, which tune-up items count, how fuel flow data helps, and which fuel-saving myths to ignore.

How to Inspect and Clean a Raw-Water (Sea) Strainer

The sea strainer is the cheap screen that keeps weeds, shells and plastic out of your engine, generator and A/C pumps. Learn how to clean it safely with the seacock closed, reseal the lid so it can't suck air, spot a cracked bowl before it floods the boat, and winterize it.

How to Inspect and Replace Exhaust Shutters and Flapper Valves

The rubber shutters inside a sterndrive's exhaust and the flappers at an inboard's exhaust outlet are one-way valves that keep water from washing back into the engine. Learn where they are, how they fail, how to check them every year, and why riser service is the perfect time to replace them.

How to Inspect and Replace Sacrificial Anodes (Zincs)

Check the anodes on your outboard, sterndrive or inboard running gear, replace them when they are half gone, and choose the right metal for the water you boat in. Fresh anodes are cheap insurance against expensive corrosion damage to your lower unit, drive and prop.

How to Inspect and Replace Spark Plugs

Pull, read and replace the spark plugs on a gas outboard, sterndrive, inboard or PWC. Fresh, correctly gapped plugs help the engine start easily and run smoothly, and the old plugs tell you a lot about the engine's health.

How to Inspect Engine Belts and the Tensioner on Sterndrives, Inboards and Diesels

On many inboard, sterndrive and diesel engines, one belt runs the water pump, the alternator and often the power steering. If it breaks or jumps off, the engine overheats and the steering goes heavy at the same moment. Learn how to inspect the belt, tensioner and pulleys, check tension, and carry the right spare.

How to Inspect Exhaust Manifolds and Risers on a Sterndrive or Inboard

Cast-iron exhaust manifolds and risers rust from the inside, and when they fail they can let water into the cylinders and ruin the engine. Learn the warning signs, how often to inspect them in salt and fresh water, how to check a riser yourself, and when replacement is a job for a pro.

How to Keep a Boat Maintenance Log and Organize Your Receipts

Set up a simple maintenance log that records the date, engine hours, work done, parts and who did it, and keep receipts and photos organized. Good records help with warranty and insurance claims, show buyers the boat was cared for and reveal wear patterns before something fails.

How to Replace a Fuel/Water Separating Filter (and Check for Water in Your Fuel)

Swap the spin-on fuel/water separator on your gas boat and learn to spot water and ethanol phase separation before it stalls the engine. It is one of the cheapest jobs on the boat and one of the best protections for a fuel-injected engine.