Winterizing and antifreeze to use in Mercruiser 4.3

[Gerhard Peters]

I'm in the process of winterizing my Mercruiser 4.3. I have drained the water from the exhaust manifolds and drained the engine block by removing the plugs near the bottom of the block.

Is it still necessary to add antifreeze to the engine after draining it? If so can I use the same antifreeze I use for my RV water lines/plumbing?

This my first boat and first time winterizing it.

 

[alldodge]

Is it still necessary to add antifreeze to the engine after draining it?

IMO if all the water is gone, then AF is not necessary

Other opinions will be along shortly opcorn:

 

[ThomW]

You won't get a definitive answer to that question.

One school of thought is that air won't freeze, so if ALL the water is out, you're good to go.

Others say anti-freeze is good because it reduces chances for rust and would help if there was a little water left in the block somewhere.

Others counter that by saying anti-freeze mixed with enough water might slush up and partially freeze somewhere causing issues.

Unfortunately, it's up to you and based upon what will help you sleep best at night. Both ways have been done for years with no issues, and both ways have been attempted incorrectly and caused problems.

I personally use anti-freeze in my engines, but again, it's really a matter of personally preference.

 

[Rick Stephens]

Air don't freeze.

 

[Scott Danforth]

make sure you changed the engine oil, and you also drained the intake manifold (drain on bottom of the thermostat area), the large hose, and the line back to the transom..... and you are good to go.

 

[stonyloam]

A little basic science here. Water begins to expand when it cools to about 40°F, and expands about 9% when it freezes. So if your block is FULL of water it has no room to expand so it will freeze and crack the block. If you drain your block properly there will not be enough water left to cause any damage. RV antifreeze will if fact freeze at about 12°F BUT will not damage your block BECAUSE RV ANTIFREEZE DOES NOT EXPAND WHEN IT FREEZES. As for the rust, for iron to oxidize you need three things, moisture, iron and oxygen. When you drain your block there is not enough oxygen left in the block to cause any significant amount of rust. So make sure your drains are clear and drain your hoses you should be good. Once the water is out if you want to add some antifreeze that is up yo you.

 

[ThomW]

One thing I'd add, is change the gear lube/oil too! If you happened to have a bad seal and had water mixed in with your gear lube, it could freeze up in your lower and cause problems.

 

[muc]

Who do you want to trust?
On one side there is the “air doesn’t freeze” and the “I’ve done it like this for XX years”.
On the other side there are MerCruiser, Volvo and high quality marine service providers.

For decades the engine manufactures have recommended antifreeze as part of “layup” and now for quite a few years they require it. Another thing that has changed. Volvo directed us to pump the antifreeze through the engine with the pump that they included on the front of the engine and MerCruiser recommenced removal of the thermostat and dumping it in the intake manifold. MerCruiser has recommended using the sea water pump for a number of years now.

You asked about using “RV antifreeze”. I assume you’re talking about the -50 pink stuff that is designed for water lines. Once again we can look at what the engine manufacturers and quality marine service providers recommend. So how many experts recommend the pink stuff? None, zero, zip, nada. They ALL recommend and use a higher quality antifreeze.

It’s your boat and you get to decide. Like I said, who do you trust?
The “internet” people?
Or
The experts?

 

[tpenfield]

I

1) Is it still necessary to add antifreeze to the engine after draining it?

2) If so can I use the same antifreeze I use for my RV water lines/plumbing?

#1 = no

#2 = yes . . . just be sure to use the proper grade (-50, -60, -75, -100) for your area, keeping in mind that the ratings are a pipe burst rating. So, give yourself lots of headroom in what you choose.

 

[Rick Stephens]

Who do you want to trust?
On one side there is the “air doesn’t freeze” and the “I’ve done it like this for XX years”.
On the other side there are MerCruiser, Volvo and high quality marine service providers.

For decades the engine manufactures have recommended antifreeze as part of “layup” and now for quite a few years they require it. Another thing that has changed. Volvo directed us to pump the antifreeze through the engine with the pump that they included on the front of the engine and MerCruiser recommenced removal of the thermostat and dumping it in the intake manifold. MerCruiser has recommended using the sea water pump for a number of years now.

You asked about using “RV antifreeze”. I assume you’re talking about the -50 pink stuff that is designed for water lines. Once again we can look at what the engine manufacturers and quality marine service providers recommend. So how many experts recommend the pink stuff? None, zero, zip, nada. They ALL recommend and use a higher quality antifreeze.

It’s your boat and you get to decide. Like I said, who do you trust?
The “internet” people?
Or
The experts?

I call full scale B.S. on that. What the manufacturers are doing is full scale CYA on warranty. By stating you have to do XY and Z, they cop their way out of most any engine warranty issue involving the block and cooling system. You can have your chapter and verse do it their way.

Rick

 

[stonyloam]

By “ higher quality” antifreeze they mean propylene glycol antifreeze WITH CORROSION INHIBITORS, which btw IS the non toxic “pink stuff” NOT toxic automotive ethylene glycol antifreeze. Just read the label when you get your antifreeze to make sure it contains rust inhibitors and both you and Mercruiser will be happy.

 

[icyb]

I drain the block and manifolds if water coming out good your ok,if it's a trickle use a piece of wire or thin screwdriver and poke in the hole,this will loosen any rust scale and the water will gush out. Take the biggest hose of at the bottom, here you will have the most water. No need for antifreeze. Find the longest hose that goes back to the transom it goes to the outdrive. This hose is the only one that I pore some antifreeze. I pore it slow and I listen for it to hit a shallow metal pan the kind guys use for oil changing.this will catch the antifreeze so it doesn't go all over my drivway. at first you will see just water that was pushed out by the antifreeze. I pore some more till I see antifreeze. Buy the antifreeze that's made for winterizing marine engines most look purple
not the pink stuff. One gallon last me about 3 to 4 seasons.

 

[Lou C]

OK I am going to say, I fall on the side that Muc does, I've used antifreeze every year for 15+ years, raw water cooled in salt water, boat sits on the mooring 6 months of the year no way to flush.
And, when I did the top end rebuild 2 years ago (head gasket failure due to previous overheat), had the 4.3 apart. What I found was surprisingly little rust inside, I wound up replacing the cyl heads not due to rust through behind the valve seats (this is what does in some raw water cooled engines in salt) but due to cracks caused by a previous overheat in 2013. That and the cooling passages were getting eroded from years of salt water cooling. But no failure due to raw water cooling.
The way I look at it:
in the salt pond we coat trailer springs/ubolts/fittings with anti-rust coatings. If you do, they last a very long time. If you don't they look horrible after 5 seasons. Adding the right A/F is to me the same thing. Except you can't see it unless you take off your thermostat housing and look in your intake manifold water passage.

But for freshwater guys, you may not see the same need. However, apparently the manufacturers now do feel that way and have for some time.

as far as antifreeze, I've used either the -100 marine antifreeze or mixed up 50/50 Sierra non tox PG antifreeze. The West stuff is expensive ($12/gallon) the Sierra works out to $7.50/gallon mixed 50/50. The -50 and -60 are not recommended if you get down to zero, if you look at the specs. They are good for mild winters that get down to approx. 20 degrees at the coldest. They get hard at +7 for the -60 and +11 for the -50. The -100 is liquid down to like -45-55*F, almost overkill. The 50/50 mix of Sierra, gives freeze protection to -26*F more than good enough here. Coldest we get is zero.

 

[Gerhard Peters]

Thanks for the help!

 

[QBhoy]

A little basic science here. Water begins to expand when it cools to about 40°F, and expands about 9% when it freezes. So if your block is FULL of water it has no room to expand so it will freeze and crack the block. If you drain your block properly there will not be enough water left to cause any damage. RV antifreeze will if fact freeze at about 12°F BUT will not damage your block BECAUSE RV ANTIFREEZE DOES NOT EXPAND WHEN IT FREEZES. As for the rust, for iron to oxidize you need three things, moisture, iron and oxygen. When you drain your block there is not enough oxygen left in the block to cause any significant amount of rust. So make sure your drains are clear and drain your hoses you should be good. Once the water is out if you want to add some antifreeze that is up yo you.

c’mon now...what makes you think there won’t be enough oxygen in the block to cause corrosion. That’s as silly a statement as I’ve ever heard. Have a think about it.

 

[QBhoy]

For me. Defo full with antifreeze.
the same guys that say air don’t freeze will also tell you in the same paragraph that make sure you poke the crud out the drains. It’s pretty obvious the crud mainly comes from internal corrosion.
ive filled mine with AF since I’ve had it and the guy before. In her 16 years, she’s never had any crud or flaking internals there. Up to you.

 

[Lou C]

I guess that's one of those things we will never know....(is there enough oxygen in a block to cause corrosion) but even as far back as '88 OMC recommended adding AF to reduce corrosion, I have it in my '88 owners manual.
Another example...common problem on many inboard boats especially in salt water....is a rusted oil pan...eventually they can rust through...I have not had to change mine...because every few years I spray it up with Corrosion X, just like the leaf springs on the trailer...
Just winterized mine yesterday….filled it up with 50/50 Sierra PG antifreeze with corrosion inhibitors...

 

[stonyloam]

Well if your block contains one gallon of air at 20% oxygen that will be about 4.5 grams which = 0.14 moles. Rust is Fe2O3, so 3 atoms of oxygen to make one molecule of rust. Molecular weight of rust is 160, so 160 grams per mole. 0.14 moles of Oxygen will make about 0.05 moles of rust which = about 7.5 grams if all of the oxygen is consumed. Since your block has about 160,000 grams of iron, I would say that is not significant (0.005%). And since you have been pumping hot oxygenated water through your block all summer the entire inner surface of the block is already coated with rust and it is unlikely that there is any iron exposed to the air left in the block. So yeah I have thought about it.

 

[stonyloam]

The reason to poke the drain holes is not just to remove internal rust flakes but also to remove the sediment that has been sucked in with the raw cooling water. Whenever you run in dirty water fine sediment (sand, mud algae) is sucked in with the cooling water. While you are running most is flushed out, but when you shut the engine off all of that stuff can settle out and eventually accumulate enough to cover the drain holes with a solid layer of sludge.

 

[QBhoy]

Well if your block contains one gallon of air at 20% oxygen that will be about 4.5 grams which = 0.14 moles. Rust is Fe2O3, so 3 atoms of oxygen to make one molecule of rust. Molecular weight of rust is 160, so 160 grams per mole. 0.14 moles of Oxygen will make about 0.05 moles of rust which = about 7.5 grams if all of the oxygen is consumed. Since your block has about 160,000 grams of iron, I would say that is not significant (0.005%). And since you have been pumping hot oxygenated water through your block all summer the entire inner surface of the block is already coated with rust and it is unlikely that there is any iron exposed to the air left in the block. So yeah I have thought about it.

But my point is....how or why would all the oxygen be consumed. The block is open to atmosphere. In an empty state (as suggested) it has literally the whole world worth of oxygen supplied to it, if it wants. Love the maths and chemistry, but it’s fundamentally not applicable here.