Antifreeze question - IAT or OAT

[cashwowud]

Hi guys,

Mercuiser 350mag/bravo3/Regal 2550

I have just winterised my engine by draining the water as you should but I of course wish to minimise corrosion of the block and manifolds and so I want to pour antifreeze in the block by disconnecting the hose that goes into the thermostat. My question is weather to use the older IAT mix or use the newer OAT type?
I know there a loads of posts about winterising and which is the best and if you should even use antifreeze but nobody mentions the type,

Thanks in advance,

cashwowud

 

[muc]

neither

IMPORTANT: Mercury MerCruiser requires that propylene glycol antifreeze, mixed to the manufacturer's instructions, be used in the seawater section of the cooling system for freezing temperatures or extended storage. Ensure that the propylene glycol antifreeze contains a rust inhibitor and is recommended for use in marine engines. Be certain to follow the propylene glycol manufacturer's recommendations

 

[bruceb58]

My question is weather to use the older IAT mix or use the newer OAT type?

Both of those are automotive type anti freeze and should not be used.

 

[alldodge]

OK, I'll step into it, and catch the flack

Poly is used because it is non-toxic and when the motor is started back up it doesn't pollute the environment. All the manuals I have specify Ethylene glycol for closed cooling, and most use Dex cool. So I can see no reason that any of the antifreezes will hurt anything in the motor.

That said using Poly is fine and good for the world, but do make sure you look for Antigel and there is no listing of alcohol. The cheap pick stuff that has alcohol in it is for water systems only and don't use it in the motor. Don't even use it in a shower sump, it can mess it up. Find the -50 Antigel dark pick stuff or the Blue'ish colored -100 stuff

 

[JoLin]

What Alldodge said. The right poly will say right on the container, that it contains corrosion inhibitors for engines. I buy mine at West- it goes on sale every fall for $3.99 or $4.99 with a mail-in rebate. My 4.3's take 3.5-4 gallons each to fill the block and manifolds, and to back-flush the cooling hose from the drive. The cheaper, $2/ gallon stuff is for water and sump systems.

My .02.

 

[Lou C]

Another way to do it is to get the Sierra brand PG antifreeze which has corrosion inhibitors in it. If you mix it up 50/50 it gives about -25 freeze protection. Much cheaper than buying the -100 burst protection (which is about -50 freeze protection) stuff from West Marine. The other ones, -50 and -60 burst protection, slush up at too high a temp for me....I put them in the freezer at zero, and they slushed up pretty hard, but did not expand. I like my AF to stay liquid! The -100 of course stays liquid but costs a fortune.

​Ace Hardware sells it, I have a PG hydrometer so I can mix up my own batch every year...better and cheaper....


​Also, here is another tip for those of you with older raw water cooled engines in salt water, to get the drains to really drain, those pics that they sell for removing hoses, work great on stubborn drains that are clogged with rust. Even better than my old thin screwdriver and stiff wire bent at a right angle!

 

[cashwowud]

Thanks for the quick replies. Where I am in the UK rarely goes below -10 deg C. I will try get some PG asap but a quick search online means I'll probably have to send for it. cashwowud

 

[Scott Danforth]

You could simply drain it.... Air doesnt freeze

 

[Oshkosh1]

You could simply drain it.... Air doesnt freeze

DAMN! Beat me to it.

I "converted" another boat owner to the "Air don't freeze" method two weeks ago!lol!

 

[cashwowud]

The only reason I want to fill with antifreeze is to slow down corrosion or am I wasting my time? I suppose you need a lifetime of experience to know and I havn't got that long left!

cashwowud

 

[alldodge]

Antifreeze does help but how much has a lot of debating going on. I'm a fresh water guy and believe if you give the motor a good flushing, you would be good, Again FW guy, need to hear from the salt guys

 

[Scott Danforth]

The only reason I want to fill with antifreeze is to .....wasting my time?

more harm than good with anti-freeze and most people fail to get the water out to begin with.

as far as corrosion, you have corrosion in the block anyway from the raw water flowing thru it.

 

[stonyloam]

The only reason I want to fill with antifreeze is to slow down corrosion or am I wasting my time?

Yes, IMHO.

 

[Oshkosh1]

The only reason I want to fill with antifreeze is to slow down corrosion or am I wasting my time? I suppose you need a lifetime of experience to know and I havn't got that long left!

cashwowud

My 25 year old block still looks very good. I have no reason to doubt it could go another 25 without AF being used...(Original owner also didn't use AF). I like being able to winterize my boat in 20 minutes!lol!

Drain the block, drain the risers, blow all drains out with a little compressed air, pull the lower unit, pull the lower waterpump hose, pull the battery...done. I'm finished before my neighbor's boat is even warmed up...

 

[QBhoy]

Guys...I know I rattle on about it, but for sure, filling the engine with antifreeze will reduce corrosion dramatically. It simple science. All my boats have been in fresh water and all of them (until this one) have had flakes of metal in the block...the ones that block the drain plugs that all the ?air don?t freeze? guys say you need to poke at to make sure they are clear.
My current boat has had antifreeze in it every year since 2003. Guess what...there has never been any flakes of corroded metal in there. I check every year. None.
Take from this what you may.
I?m not saying the block is going to rust through if you don?t...even perhaps after 30 years...but it?s clearly not good !

 

[QBhoy]

As for the corrosion anyway with raw water flowing through it theory. Not really applicable, I think. As long as there is some sort of liquid (reducing the exposure to atmospheric O2 levels and ideal rusting conditions) in there, which there is during the season (it doesn?t drain itself when not in use in the summer !), it isn?t really corroding the same way it would when empty and in cold damp winter storage.

 

[bruceb58]

One of our boats with a 5.0L Chevy had 1000 hours on it when we sold it. If you took off the thermostat housing and looked inside, very little corrosion.

No need for antifreeze.

 

[QBhoy]

How old was it Bruce and where abouts was she used ? Did you have to poke at the two block drain holes to clear the crud ?

 

[bruceb58]

Was 10 years old when we sold it. Didn't have to drain the block often since it was in California most the time. However, the area at the thermostat did not have water in it so it was always exposed to air.

The thermostat housing got way more corroded. It must have been a different metal than what the block was made of.

Half of the hours were in salt water.

 

[Lou C]

I used to think that what you saw in the bottom of the intake manifold under the t stat housing was representative of the rest of the engine but when I took mine apart I learned that wasn't true. What I found was that the cooling passages in the head had eroded to the point that if the heads were re surfaced, these cooling passages would be too large to seal properly on a new head gasket. I wound up installing a pair or re man heads. The block cooling passages were in better shape and the machinist and a few mechanics I know felt that the heads tend to rust through before the block (the heads will rust through behind the vslve seats).

So there an be different levels of corrosion in different parts of the engine. The t stat housings rust worse because they are not full of water with the engine off as the intake manifold is. Same with the exhaust risers (elbows) and the exhsust manifolds; the risers always rust more and this is because they are more exposed to air than the manifolds. So I do think anything you can do to slow down corrosion is worth it just like rinsing the trailer and spraying the springs and fasteners with Corrosion X....

So far I'm on my third thermostat housing and third exhaust system in 15 years of salt water use.