How to winterize your motor without draining the water.

muc

"Retired" Association of Marine Technicians...
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How to winterize your motor without draining the water.

How’s that for clickbait?
I’ve spent over 30 years as a marine mechanic in Minnesota, so after winterizing over 3000 engines (without breaking any) I do have some thoughts on putting a boat to bed for the winter. What I don’t have is the patience that the late Don S had to reply to all the posts where people gave bad (if well intentioned) advice. So here are my thoughts and I will explain, how a boat yard winterizes without draining the water.
First is fogging the motor. This is a lot like the anti-freeze debate. I see people give advice without knowing what conditions the boat will be stored in ( or even what motor they have!) and that really matters when you make the decision on whether you fog or not. How much moisture is in the cylinders and on the valves and whether that moisture remains frozen most of the winter (like if the boat is stored in an unheated barn) or it thaws and refreezes on a daily basis (like if the boat is shrink-wrapped) should influence what you do. I have torn down more than a few motors during the winter that have been fogged down the carb, fogged by running on 2 stroke oil mixture and nothing done at all. ALL of them had some rust in the cylinders and on the valves, but there was less rust in the fogged motors.
Now, how to fog. 3 ways to do this. 1. Pull the spark plugs and spray some in --- probably the best for a carb or throttle body engine, but takes way too much time for somebody who has to get 5 to 10 boats done today. 2. Dump the fogging oil down the carb, works good on most carb engines but can cause serious problems on engines with certain intake manifolds or EFI engines. 3. Running on remote tank with the fogging mixture the manufacturer of your engine recommends. This one is a really good idea, especially if you have electric fuel pumps or injectors. And is what is recommended by most manufacturers.
Should you fog or not? If you’re in Minnesota or a similar climate, my recommendation is to fog, done right it helps more than it hurts. If you’re somewhere else, ask somebody in your area who has torn down engines stored both ways for their advice.

Next is getting the water out. Drain it! Air don’t freeze. But is there a better way? Of course there is, it’s called antifreeze and is required or recommended by most manufacturers. Once again there are a lot of variables involved in if you need to or you should. I feel the biggest reason MerCruiser now requires antifreeze is due to all of the different metals and alloys that make up the new engines. Gone are the days that the only metal the water touched was cast iron, there are now multiple alloys that will interact with each other. That’s why the anticorrosion additives are now so important. Is it worthwhile using antifreeze in a cast iron block? Based on 30 years as a marine mechanic in Minnesota I feel it is. I’ve done it both ways and there are less rust flakes when antifreeze is used. I’m really sure that if you have a “single point drain” setup you will have trouble down the road if you don’t.

OK, here is how a boat shop can winterize an engine without draining the water first.
It has to do with the non-tox antifreeze we use. Its 100% polypropylene glycol. This stuff is roughly -200° burst so when you mix it with an equal amount of water you get -100° and when you mix that with an equal amount of water you get the -50° burst that most of the pink non-tox that you get at the big box stores. Let’s stop and talk about the pink stuff at the big box stores. I don’t know about other parts of the country, but here in MN most of this stuff uses Ethanol as the ingredient that keeps it from expanding when it freezes and has nowhere near the anticorrosion additives that are required by MerCruiser or that are requested by Volvo. I have no idea if alcohol is bad for the cast iron or aluminum that engine blocks are made from but I’m pretty sure it’s not good for the hoses, impellers or seals. The one year we used the cheap pink for water systems, we did have some water pumps that acted up in the spring and I think the alcohol might have been the cause of the check valves in the pump I disassembled not sealing. So if you want to use the cheap pink non-tox to flush the water out of your engine. I highly recommend you make sure to drain it all back out before leaving the boat for the winter. OK back to how almost every big boat shop in MN winterizes. We take 60-90 gallons of the 100% and mix in enough water to thin it out enough so an impeller pump can move it. Some of the shops will put this in a roofing tar trailer so it can be preheated, some will have it in a big tank and run it out through an instantaneous water heater but most shops just let the first few boats run long enough to heat it up enough so the thermostat in the engine opens quickly. This antifreeze mixture is then pumped to the engine, sometimes thru muffs for I/Os, sometimes thru an adapter we screw on the sea water stainer. The engine is run for 5-7 minutes after the thermostat opens. All the antifreeze that comes out of the exhaust is captured and pumped back to the main tank to be used again. Thru out the day a refractometer is used to monitor the concentration of the mixture and almost all of the engines will have a sample taken at one of the block plugs to be sure that the engine is completely protected.
Most of the time we will drain the block, manifolds and coolers first --- if they are fairly easy to get to --- so that the antifreeze doesn’t get diluted as fast. Some shops that I know of will drain the antifreeze out of the engine to reuse it. But the better shops leave it in (one of the reasons some shops charge more) for the protection that it provides during lay up.
Now, why we winterize this way?
1. It’s better for the engine and now required to maintain warranty coverage.
2. We don’t have to worry that a “junior” technician will miss a fuel cooler, engine oil cooler, ect.
3. Some boats are almost impossible to get to some of the hoses or drains.

This is from one of the newer MerCruiser owners manuals
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.

Volvo covers the use of antifreeze in service bulletin 05-2-2
Here is some of it
Disconnect the suction hose at the water intake.
NOTICE! Close the water intake tap if this is carried out when the boat is in the water!
Put the end of the hose in a bucket filled with freshwater, start the engine and run the cooling system clean
from seawater until the bucket is empty. Turn off the engine.
NOTICE! NOTICE! The water intake tap must remain closed if this is done when the boat is in the water.
 
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Lou C

Supreme Mariner
Joined
Nov 10, 2002
Messages
11,798
Thanks, now I feel that I did not waste money doing it the drain-and-backfill way all these years. I have used either the -100 marine AF sold by West Marine and others, or mixed up a batch of Sierra PG no tox antifreeze which is very good also since it is intended to be used in engines.

​I know people that gamble with the suck the AF up the drive method (without draining the block first) but have not done it that way because of the concern with the thermostat not opening all the way. I have thought of putting a trough under the drive and pressurizing the AF flow with a bilge pump and positioning the trough to make it catch the exhausted AF, so it is re-circulated which will allow it to heat up enough to keep the stat open but its just easier, simpler and less messy if you can get the drains, to drain and then back fill.
 

89retta

Senior Chief Petty Officer
Joined
Jul 18, 2010
Messages
772
Very good read and points. I live way up here in Edmonton,AB, Canada. And pretty much all the shops here including myself use the pink stuff. I do like the idea of using regular antifreeze like they use in most cars. My only concern with that is come spring time people firing up the boat and dumping it in the lakes.
 

Lou C

Supreme Mariner
Joined
Nov 10, 2002
Messages
11,798
If you want to use regular automotive antifreeze the only one to use is Propylene Glycol Sierra antifreeze. It can be mixed 50/50 or 60/40 just like regular ethylene glycol antifreeze but it is non toxic. It does not give the same very high boil very low freeze points as EG but it will be good enough. 50/50 gives you -26 freeze protection. Higher percentages will give more...
 

JimS123

Fleet Admiral
Joined
Jul 27, 2007
Messages
7,952
I know people that gamble with the suck the AF up the drive method (without draining the block first) but have not done it that way because of the concern with the thermostat not opening all the way.
The OP's method does not include draining first if the ports are not easy to get to. So, maybe that is an optional step.

This method is highly controversial on this board. In fact, I'm waiting for the naysayers to criticize. The key to a successful result is the refractometer that the OP mentions. I've said that many times, and it seems to always go over the posters heads.
 
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