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I was browsing the site for tips on winterizing. When we purchased our used boat, it was winterized by the dealer, and filled with antifreeze.

We have a flushpro, so we can warm up the engine, do the oil change with water. Then switch to "suck the antifreeze out of a container", and fill the system until it comes out of the exhaust.

The question is do we have to pull all the drain plugs, drain the water, and replace the plugs before we put the antifreeze? I have seen conflicting comments on the site on whether it is necessary.

Also, does anyone know how much RV antifreeze is needed to fill the cooling system of a Indmar 8100 425hp?

Any advice would be appreciated.

Edited by MN_LSV
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You will probably see 10 different answers in 8 posts on this board so I'll chime in with mine.

1. I drain the block completely.

2. My engine manufacturer (Mercruiser) recommends filling the block back up with AF for the intent of corrosion prevention.

Erring on the side of caution, I immediately drain the water as soon as I pull the boat and then refill the block with the -100 AF through the Tstat while it's still open. (it gets cold where I store it)

If you crank up the nose on the trailer, you will add about 4-5 gallons of AF, which is probably overkill. My rationale is that if there is any water trapped in the block, it will get diluted with the AF.

BTW, if you have a sea-strainer, empty that while you are draining the water.

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If you're using the pink RV antifreeze, you will need to drain all the water first. You do not want to allow the pink stuff to be diluted. It needs to be put in straight from the jug. Any water left in the block will dilute it.

Don't know how many gallons you'll need for that, but I'd guess maybe 5?? Somebody else may have a better answer. I don't have a flush pro and I don't use the method you mentioned. But I used 3.5 gallons for the motor and heater and that doesn't fill it completely to the point where it's running out the exhaust. You have a bigger motor too so I'd buy 5 and maybe you'll take one back.

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I don't think the flush pro will 'suck the antifreeze out of a container.' It works with water pressurized from a garden hose.

Drain the motor, ETC, first. Do you have a shower? Heater? Ballast? You want pure antifreeze in the system.

If you are going to run the AF through the system (as opposed to pouring), five gallons EASY. I'd buy seven.

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