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Marine Engine Winterizing Tips

Marine Engine Winterizing Tips

Marine Engine Winterizing Tips

Whether the weather is good or bad this winter, winterizing your marine engine should be at the top of your to-do list. Don’t worry though, Boatworld has done the hard work for you. Well, we compiled a list so the heavy lifting has been done.

Flushing your Engine

After a hard season on the water, your outboard will need a good flush out with a flush mix. Here at Boatworld, we make our own in-house corrosion inhibitor Called Blu Thru. Not only is Blu Thru made in the UK by the trusty Boatworld team. It is cheaper than the alternatives and comes in an easy to store tablet form instead of being a liquid. Blu Thru is usually used on running engines but it can be used on an old rusted engine. Soak the component parts in Blu Thru for at least a few hours maybe a day and see how Blu Thru transforms your engine.

Marine Engine Winterizing
Blu Thru Flushing Kit


The number 1 problem with outboards whether it is winterizing an engine or a general problem, is the fuel. The fuel is the most important part of running an outboard. Always make sure you use fresh fuel that has not been left in a shed for 6 months and always use a funnel with a gauze in it to stop any nasty particles getting where you don’t want them. Old and dirty fuel is the No1 cause of clogged fuel injectors and carburettors.

If you are not going to use your Outboard or Boat for 30 days or longer it is worth draining your fuel. Small deposits of fuel left inside the injectors, Carb float bowl or jet can gel and solidify. This results in you or paying someone to take the carb off your engine and clean it out thoroughly which will take a few hours.

Martyn Wilcox of Tohatsu says:

Water in fuel is becoming an increasing problem because people don’t carry out end-of-season servicing and winterising. Use of a fuel stabiliser can overcome this issue.” He also recommends the use of ‘fogging oil’ to prevent corrosion.

“Many steel and cast components are used in the construction, so internal components can be very susceptible to corrosion if not protected correctly,” .

Marine Engine Winterizing
Water in Fuel

Drain Engine

This is not so important for outboard users but is critically important for inboards and sterndrive engines. Most newer inboards have an easy drain system so just make sure that has done its job. For older engines, you can buy some coloured antifreeze and pour it through your hoses and exhaust manifold if the coloured antifreeze runs through all the water has been pushed through. Outboards self-drain just tilt the outboard up on the trim bracket and any water will drip out.

Prop and shaft

While you are winterizing your engine you might as well take the propeller off to make sure no fishing line or weeds have been sucked in. While the prop is off your engine you might as well check the prop for damage and check for straightness. If there is any damage, while your engine is out of the water you may as well get the prop retouch or buy a new one. (Some props can be found for very cheap). Before reinstalling make sure you coat the prop shaft splines with marine grease. While you are already looking at that end o the engine check for skeg damage, paint abrasion and corrosion. Fix any damage if needed to keep your engine looking and feeling like new.

Marine Engine Winterizing
Rusty Prop


Inside the Cowling

Fogging means to protect the inner workings of an engine with a coating of lubricant. During storage, your engine’s steel parts (valves, camshaft, piston rings, crankshaft, bearings and connecting rods) need a film of lube to keep them from corroding. There are multiple ways to do this and many concoctions to use. We recommend wd-40 and Duck oil

You Can Never Have Too Much Grease

(Well that’s what our outboard engineer Gary says)

Keeping moving parts moving freely ensures you won’t have sticky issues next spring. With a grease gun filled with waterproof marine grease, lubricate all fittings noted in your owner’s manual. Just as important, wipe away all remnants of dirty, old, hardened grease with a rag soaked in WD-40 or similar lubricant. That hardened grease will eventually bind up; steering cables are a great example of this issue.

Marine Engine Winterizing
Greasing up parts


Anodes are typically placed in strategic locations as sacrificial elements, so when they are too eroded to do their jobs, they should be replaced. Check your owner’s manual for the location and proper removal and replacement of anodes.


The best way to make sure you have no problems when next year comes round is to follow the above guidelines and make sure your outboard/engine is well looked after over the winter period. If you are not able to winterize your engine yourself find a local engineer or outboard shop and they will happily winterize your engine for you. I personally think the best time to get your engine services is around winter time as you have no need for it and can sort out any unexpected problems that may have come to light over the summer months. We hope that you have found this blog interesting and useful. If you need any more information or help please feel free to get in contact with us.

Boatworld UK


To call us click here 01246 453815

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