How To Winterize Your Volvo Penta Or Mercruiser Engine

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Saves £££'s this winter by carrying out your engine winterization yourself, heres our handy guide, to help you through the process.

Please note that some people have slightly different ideas and procedures, but we are all searching for a common goal – to prevent damage caused by corrosion and freezing bvoth internally and externally. Remember our principal enemy here is WATER!

First off, we need to ensure our fuel is free from contaminants and water. Using a good quality water absorber fuel stabiliser pour the recommended mixture into your fuel tank. In our case we usually use starbrite ez-store ez-start or water absorber as they are proven products at a reasonable price.

Now fill your fuel tank to the brim (sorry, this can get a bit expensive!). This prevents condensation forming at the top of the tank, potentially contaminating your fuel.

It is also worth changing your fuel filter, ensuring it is primed with a little fuel mixed with your water absorber.

Now that any fuelling issues are hopefully resolved, we can move on to the bigger stuff.

You will need a pair of flush muffs for the next part. These fit over the water inlets on the sterndrive and allow you to flush water through the engine whilst running out of the water.

Connect these up to a fresh water hose and turn on your water supply.

Start up your engine and run it for 10-15 minutes to allow the engine to reach full temperature and to ensure any remaining salt water has been flushed out of the engine.

Now that the engine is up to temp, it is worth changing the oil and filter if it hasnt been done recently. This prevents any harmful contaminants or water from sitting in the engine over winter.

Now for the most awkward bit. You will need to employ a friend / helper / glamorous assistant at this point.

Disconnect your fresh water supply but leave the flush muffs on the sterndrive. Make up a system to pour through a funnel into the sterndrive. We use a funnel and a piece of hose about a meter long, jubilee clipped onto the funnel at one end, and the flush muffs at the other.

Mixup a nice 50/50 mix of antifreeze/ water.

Restart your engine and let your glamorous assistant pour the antifreeze mix into the funnel and through the sterndrive. Continue running the engine until you see the blue of your antifreeze run out of the exhaust outlet, and then pour roughly a household buckets worth through. Then switch off the engine. This is the tricky part. Climb back to your engine and remove the flame arrestor on your carburettor (or intake pipe on EFI motors). Now you need some fogging oil. This will prefent corrosion to the engine internals during layup.

Restart your engine and set the revs to around 1500rpm and spray fogging oil into the inlet. Do this until the engine starts to cough and stutter. Reduce revs to tickover and continue spraying until either the engine dies or 5 seconds. Then shut down the engine completely. The engine will not be restarted, so thats all the running you will be doing for another season! Two important things to note: This process must not take longer than 15-20 seconds. Your running the engine dry and any longer than this can cause impeller damage. Secondly we dont recommend spraying fogging oil into a running diesel engine! This is very likely to cause the engine to ‘run on’ and increase revs due to the engine becoming fuelled by the fogging oil.

Now the most complicated bits are out the way, its time for a little preventative maintenance. Disconnect your battery and grease the terminals (unless you need an auto bilge pump to work). The battery should be regularly charged and discharged over winter to preserve its longevity.

Next, to prevent the belt shredding we mentioned in the last blog post, loosen off your belt tensioner (usually a 17mm nut on a toothed tensioner) and remove your drive belt(s). Next, give you pulleys a quick wire brush or sand to remove any loose corrosion. This helps to prevent corrosion build up during storage that can cause excess wear and premature belt failure. Once this is done you may wish to grease your pulleys. This will prevent moisture getting to the pulley causing corrosion. Remember to THOROUGHLY remove any grease when you relaunch though!!

It is well worth using corrosion guard or a similar product now to spray around the engine and drive, paying particular attention to electrical connectors and any exposed bare metal. Whilst your spraying, make sure to grease and lubricate any steering connectors or linkage parts.

If you can, remove the impeller. It is worth noting that impellers are a service item and should be replaced if they have any signs of brittleness, small cracks or after around 2 seasons use.

Nearly there!! Before we finally put the boat to bed, give the bilges a good clean to get rid of any moisture or damp that might be lurking. If possible leave the bung out of the boat so that if any water does find its way in it is able to drain out. Remember that the bung is missing when you relaunch! If you can, try and get a small tubular greenhouse type heater into the engine compartment. This will keep the compartment warm and moisture free, as well as hopefully reducing the risk of frost further. Ensure that the boat has a good quality, breathable cover over it to help keep it clean and dry during storage.

Finally, take a peek at your sterndrive, checking all the bellows are in good condition and crack free. Again, these are service items recommended for replacement every 2-3 seasons. If there is any hint of cracking or wear, REPLACE the bellows before launch. A leaky UJ bellow can kill a sterndrive, a leaky exhaust bellow can sink a boat! Some engineers like to remove the sterndrive for storage. This is not particularly necessary, but worthwhile if you are going to be swapping bellows out. Remember to use forward gear if you are removing the drive.

Now is also the time to remove your prop if you wish. This prevents the prop from becoming seized over the winter.

Last but not least, check your sterndrive oils level and condition. If it looks to have contamination of any form, replace the oil with a fresh tub or two of your specified brand (hi performance gear lube, ep90 etc depending on application).

And that, finally, is it!

It may seem like a lot, but its all fairly simple and very easy to do for a competent DIY’er. An hour or two on an autumn Saturday should see you done and dusted and your boat in great condition to fire up in the spring.


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