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Winterize 2003 Monsoon

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Hey guys. Time to winterize here in Canada. First time working on my new to me Monsoon 335. On my old boat i sucked AF through with fake a lake, i dont have any help this year so i wont be able to use that method. Since im storing the boat in a heated garage i want to manually add AF for corrosion protection. My question is, do i remove the thermostat and add to the block there? 

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4 minutes ago, KDCr7 said:

 My question is, do i remove the thermostat and add to the block there? 

You could do it that way, or remove one of the fittings adjacent to the thermostat (temp sensor or plug) and add it there.  But only after draining the water from all the normal drains.

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Yes absolutely will be drained first. Shes warming up right now to prep for oil change and fogging. I like the idea of manually adding AF as a last step. When i used fake a lake to suck it in, i always had to time it right  to fog while the last jug of AF was going in. This way i dont have to worry about running dry. Thanks a lot!

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10 minutes ago, KDCr7 said:

Is this my knock sensor? Doesn't look like any ive seen posted.

Yep, just don't reinstall it with Teflon tape.  The sensor gets it ground through the threads, and the tape can isolate it.

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FWIW, the anti-freeze in the block is overkill but definitely blow some RV anti-freeze through the heater core if you've got one.

My dad's boat with the same engine as yours has survived 17 years in Northern Wisconsin without ever having anti-freeze in the block.  Just need to make certain you've drained everything down correctly.

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I did do the heater core. The boat will be in heated in garage as well so definitely overkill. I guess its habit from using AF for over ten years on my Euro Skier. I was wondering if the 2 block drains (as well as exhaust and hoses) are the only spots for draining? I could be wrong but seems like the motor sat level in the Euro and is tilted to the back in the LXI. Just want to make i drained completely. I did drop the front down with the jack and got a little extra water trickle out.   

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Blow air through the heater core.

Everything else drain the water.  Antifreeze, not worth the money.  Does air freeze?  That is all that is letf if you drain all the water.  

Sixteen years, same boat, same motor, same process, no issues....... and..... more money left in my pocket.


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Yeah your right. I'm nitpicking when i should be methodical. First winter with the new boat so I just want to be sure its done properly. Its all done now and ready for next summer. Thanks for the info. 

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Drain down manifolds using the garden hose connector.

Pull the plug and knock sensor.  Stick a pencil up inside there once the water stops flowing to make sure a flake of rust didn't block the hole as that can happen.

Pull off raw water hose either intake or output.  Either works.

Drain heater and blow RV anti-freeze through the core.

Drain shower if you have one.

Pull lanyard and crank engine over for a couple seconds.

Reconnect everything and be sad for 6 months.

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The hot side can get lots of rust and scale in that side of the system.  When I serviced my shower I removed a lot of debris and the stream returned to normal.  The nipple on the block has a relatively small outlet, so make sure that isn't clogged too.

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I am one who likes to use RV antifreeze. I fill after all work has been completed. I pull the two main water hoses and fill the block. then pull the exhaust hoses and run some in both. Sometimes I even get it out of the exhaust outlet. My boat takes five gallons to get the block and exhaust to come out the outlet. It will then allow you to put the knock sensor back in and requires all drain hoses to be closed so if you reinstall the hoses at the top of the engine , main water and exhaust both. Now you are also ready for spring as engine. I leave T and rear plugs out.  I do not have any rust on the drain plugs and I never get rust out of the block. 11 years old and looks like new. As said you can do without antifreeze but then you do get rust. When I drain I see no rust from the block!  Keeps me :biggrin:.


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18 hours ago, mackie12 said:

so a guy should pull the knock sensors for the winter.......?

At least to drain the block, yes. You can pop it back in when you are sure there is no water left. I put a dab of oil on the threads too.

Steve B.

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1 hour ago, tvano said:

i've lost two shower pump diaphragms while using rv antifreeze.

zero issues after 15 years of sierra.

Ethanol based antifreeze is hard on rubber.  Propylene based antifreeze (Sierra, Stabil, etc.) is what we should be using.  From another forum:


RV/Marine non-toxic antifreeze is probably the most misunderstood commodity in our industry today. There are currently three different varieties on the market at three very different prices.

  • Propylene Glycol based: This product is only available at your local RV shop (and not every RV shop for that matter).  Like the ethanol antifreeze, this product is non-toxic and safe for all RV plumbing. However, propylene glycol does not have the same fire safety warnings, nor the risk of tainting your RV plumbing system. Furthermore, propylene glycol is a lubricant and will actually work to extend the life of the seals in your faucets and toilets, unlike the ethanol based products.


  • Ethanol (alcohol) based: This type of antifreeze is most readily available in hardware stores and most RV shops.  However, this product is also extremely flammable and not to used around any sort of pilot flames or cigarettes. As well, this product has been known to taint certain RV plumbing systems and is only to be used with Quest or Pex plumbing lines. If you have ever used this product you will quickly remember how bad you water smelt and tasted the next spring. Furthermore, because this product is made from alcohol it works to dry out all the rubber seals readily found in your faucets and toilet. As a result we do not recommend or sell this product.


  • Propylene/Ethanol Blend: Again this product is non-toxic and completely safe for RV plumbing systems.  This may seem like a good idea, however, it is unknown how much ethanol is required to taint RV plumbing lines and dry out plumbing seals. For that reason we do not recommend this product.
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  • 2 months later...

This is my winterization set up. Flush pro valve makes it pretty easy if you are an AF’er. 

Drain water

Hook up hose and pvc pipes to capture AF

Plug in pump and start engine. Let run past 160* for a few minutes

Shut down engine,  R&R oil and filter. 


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