Outboard Engine Checks and Maintainence


Let's be honest, most of us see a sunny day ahead and just want to start the engine and set off. The success of this often rests with the condition that we left our outboard engines in after our last outing, and also how we've generally maintained them. 

Shoreside Marine Services, based on the South Coast and who specialise in Engine Maintenance, Service and Repair have produced a handy crib sheet below, with some great pointers on how we call all do the best for our outboards. It also includes some advice on what we should look out for and some "tell-tale" signs of problems we could encounter.

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Understand your engine

Whether new or second hand, all engines will have been produced with a manual. Our advice is to read the manual thoroughly or obtain a copy from the manufacturer if it's a pre-owned engine. Whilst some of the technical information contained may make no sense at all, it will give you a basic overview of your outboard engine and the features it has. There should also be advisory notes on service intervals which we recommend you follow to the letter. 

Manfacturers reputations rely on the overall performance and condition of their engines. The service intervals they recommend reflect what they know about the engine build, the parts they used and how to achieve and maintain the best performance.

Know the basics of how an outboard works

Knowing the basics of an outboard and how it works will give you a good understanding of what to look for. It will also demonstrate why you need to maintain your engine and help make sense of the processes you should follow.

Basically an outboard engine comprises of a motor that when underway will power (via a vertical drive shaft) the propellers. The ignition, running and combustion process of fuel and the engine will cause heat, which needs to be cooled. Outboards are cooled by water being flushed through them.

Although that sounds pretty simple, an outboard is made up of various components which we'll cover in this article. We'll also explain how you can maintain these components and what to look out for.

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Spark plugs, wires and coils

A spark plug does exactly what it says, it delivers an electrical current to the combustion chamber of an engine for ignition. The wires and coils (depending on your engine) assist this process by conducting the electrical current. These are all important parts and they do have shelf-lives. There's no strict rule on lifespan, but it's always worth keeping a note of how your engine fires up and keeping a spare set close at hand should you need them. As a general rule, the more use the engine gets, the quicker the spark plugs can wear out.

Water pumps and impellers

Engines are cooled by a circulation of water. The impeller acts as the pump which pushes the water around. Over time, these can become worn or perished so they should be replaced every year - should it fail, it can cause major engine failure. If you run aground this can also have a serious effect on your impeller as you may suck in sand or mud through the intakes and cause damage to the pump or the housing, so always check for tell-tale signs after impact.

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Water in the fuel

If you were filling your car with fuel at a petrol station and someone said, "Why don't you just fill it up with water", you'd say "Don't be mad, it'll damage the engine".... Considering the very wet environment outboards operate in and some potentially corrosive qualities of fuel additives, along with the fact that quite simply some parts will fail over time, you should always keep an eye out for excess water in the fuel tank. Some engines will have indicators to help with this, but if not, try to keep a mental note of how your engine performs each time you're on the water as reduced performance can be a sign of this. A good recommendation is to fit a bulkhead fuel filter if you don't already have one as it's your first line of defence.


Always use fresh fuel. This may sound obvious to some and strange to others, but older fuel can become unstable and breakdown. That's also why it's important to empty fuel tanks and lines when your boats not in use for a period of time. We'll cover flushing your engine later in the article. Change the fuel filters according to the manufacturer's guidelines or your mechanical engineer's advice, and always ensure any fuel additives comply to any of their guidelines or recommendations.

Keep your engine parts moving

An engine is a machine with mechanical parts. Keeping these parts moving by regularly giving it a spray of WD-40 or a similar product will help your engine to operate smoothly and reduce repetitive abrasive contact - it will also work as a water dispersant. Whilst engines should be well lubricated, they shouldn't be swimming in product and regular application is better than "dousing" infrequently.

Checking the oil should also be a regular task. Keep an eye out for oil that might be whitish in colour as this could indicate it's been contaminated by water, conversely, if the oil has a dirty grey hue to it, it can mean that particles have entered the oil. In both cases, the skills of a qualified mechanic should be employed to diagnose the problem. Oil samples can be taken and the problem can then be diagnosed. Another tip is that when you change the oil in accordance with your manfacturers recommendations or inline with the general usage of your engine, don't forget to change the oil filter.


We recommend you flush out the engine after each use. The corrosive qualities of heat, salt-water and metal combined should never be underestimated. If you let them take hold and build up over time, they'll be twice as hard to remove at a later stage. Your manual will tell you how to complete the process for your make of engine, but if you don't have the manual why not ask a qualified mechanic to demonstrate the process (they'll usually have some good advice on how to do this quickly and efficiently). There are many products on the market that help to remove salt and can benefit the flushing process (as with all ancillary products it's worth checking the suitability for your type of engine).

Keep it clean...!

As a general rule, simply check your engine by taking the cowling (the cover) off and inspecting it for water, debris, fuel or anything that shouldn't be there. Changing sacrificial anodes when they seem "half-baked" means they'll always be at peak performance and doing their job as well as they can (after all, they're designed to give their lives in the fight against corrosion)...


This article was kindly prepared by Shoreside Marine Services


Shoreside Marine Services

Providing engine servicing, maintenance, repairs and a host of other marine services along the South Coast and throughout Hampshire and Dorset.

Our team of qualified engineers understand how important it is for you to have confidence in your boat when out at sea, and with our years of marine expertise you can be assured that your boat is always in safe hands.

We make sure your boat is ready for the water with professional and affordable engine servicing, full boat management, repairs and reconditioning. We also carry one of the UK's largest parts inventories, from batteries and engine to electrical parts and propellers. If you ask us, we'll most likely have it...!

A little of what we do....

  • Inboard Service
  • Outboard Service
  • Engine Re-builds and Installations
  • Electrical Inspections and Repairs
  • Boat Management and Gardiennage
  • Winterisation and Pre-Season Checks
  • Repairs, Refits and Refurbishments
  • Trailer Servicing
  • Polishing and Gel Work
  • Breakdown Repair Service

"We want you to enjoy your time on the water and not worry about the maintenance, servicing or repair of your boat. That's why we pride ourselves on being part of your adventure to ensure you get the most out of your time afloat"...   Dan James - Founder

Shoreside Marine