View Full Version : Winterizing

11-03-2011, 05:35 PM
Looking at winterizing a 350 Mag w/Alpha drive with "open" cooling system (did not do it last year and paid the price with cracked block, heads and exhaust). Have researched and plan the following process (boat stored on a trailer in unheated storage facility in Georgia (near Lake Lanier).

1. Add stabilizer to fuel.
2. Connect fresh water via "muffs" (garden hose) and start boat.
3. Let run till up-to-temp and thermostat is open.
4. Shutdown engine and remove flame arrestor.
5. Connect 5 gallon container, with coolant, via short garden hose to "muffs" (container higher than "muffs") and run till coolant is seen running out of the exhaust pipes.
6. Spray "fogging oil" into carb till engine stalls.
7. Open all drain values and drain new mixture.
8. Remove each spark plug, spray each cylinder with fogging oil and reinstall plugs (plugs only have 20 hours on them).
9. Top off fuel.
10. Lower outdrive when parking for season.

Question that I have are:

Step 7: Should I drain as much of the new mixture or leave full until spring?
Step 9: Read to just go 3/4 of a tank for "expansion" but feel that full would be better to stop moister within the fuel tank and not worry about "expansion" since it will be colder than when filling tank.

Should I remove pipefittings plugs from risers too (if I am draining block)?

I realize that I should change the oil but it only has about 4 hours on it and the outdrive just has 20 hours on the drive fluid.

Any input would be great......

11-03-2011, 06:18 PM
i am in a colder climate then you i perfer to drain the antifreeze after it runs thru the motor for a few minutes. one thing i would do is run a wire hanger thru all the drains to make sure any sand mud or gunk is out. if you plan on leaving it wet do this while the block is full of water.

with gas i like full topped off with stabilizer if non ethanol , if ethanol run it til it is empty.

11-03-2011, 06:19 PM
I am no expert concerning winterizing. However, I would change the motor oil and the drive unit lubricant as well. Oil is relatively inexpensive and I certainly would take the time to change it. The cost of the materials versus the cost of hard parts seem to justify the time and expense.

I have always been told to try to fill the gas tank to its maximum to eliminate getting moisture in the tank. Especially with todays fuels I would not take the chance of leaving the tank anything below full. I have always had great success with Sta-Bil gas treatment.

Good luck.

11-03-2011, 09:08 PM
Been doing this stuff for over 40 years, to run anti freeze through the way you describe does not work. As soon as the cooler anti freeze mix hits the thermostat it will slam shut leaving the block 90%+ empty! Having a a ton of boats over the years up here in NY the most fool proof way is:: Run to temp change oil and filter, fire it off and fog it out with the fresh oil. Now drain the block and manifolds then close the cocks, now remove the circ pump hose at the Tstat housing put a snug fitting piece of PVC pipe in the hose. Use a funnel and pour the anti freeze in slowly until it comes out the Tstat housing, put the hose back on. Remove the two manifold feed hoses and pour anti freeze, use a funnel pour anti freeze in until you hear it trickle out the drive or pipes. Last but not least pull the hose off the power steering oil cooler to drain it. Grease all fittings and WD40 any thing that is or will rust! You can use cheap -50 RV anti freeze, I now work at a fairly big marine parts house, believe me no one uses the real stuff. I know of two contractors that are using 99 Cent windshield washer fluid, they don't like me any more I bioched them out a bit. Phil

11-03-2011, 11:57 PM

Could you clarify something for me? I don't understand what you are saying about the "cooler" antifreeze mix slamming the thermostat shut. Isn't the antifreeze likely to be about the same temperature as the water running through the hose? Or quite possibly warmer, if it's come right out of the indoors (from a store or one's house)?

Put another way, if you ran the boat in a lake full of antifreeze, wouldn't the thermostat and the rest of the cooling system do the same things they normally do, but with antifreeze instead of water? Meaning that to keep the thermostat open, what's critical is getting the engine up to the needed temperature, regardless of whether there is cooling water or antifreeze being run through, and what temperature that water or antifreeze is on its way in?

Or does antifreeze have a huge specific heat compared to water? Such that antifreeze absorbs far more heat than water, or absorbs heat more quickly than water, from the block? I did some looking and my first take was that the opposite was true. If this is right, I would expect that water should cool the block more efficiently than an antifreeze or antifreeze/water mix. (http://www.engineeringtoolbox.com/ethylene-glycol-d_146.html)

I know you have tons of experience--I just feel like I must be missing something here.

Regards and thanks,


11-04-2011, 06:28 AM
my setup is close to fixx's i use a bilge pump and drain pipes that drain into a 5 gal bucket with 4 gallons of antifreeze i run the boat that way for 10-15 minutes until it's all warmed up. not sure it would work on a muff system they always seem to lose water the kiddie pool would work, my setup has flush valve.

don't have pics or vids can't take them either the setup was re-assigned as a sump pump for my basement during the power outage we had during the octobo'easter we just had.

Carl C
11-04-2011, 07:58 AM
Change the oil and run the engine to circulate the new oil. My oil only had about 4 hours too but I changed it.
I also pulled the drive to check engine alignment, u-joints, gimbal bearing and changed the gear oil. The fresh water cooling stuff IDK. I back flushed my closed cooling system one component at a time to remove any sand (there was none).

As far as the fuel thing you will find a lot of opinions. Since my boat is stored uncovered indoors I don't worry about how much fuel is in it.

11-04-2011, 09:01 AM
I do essentially what MOP has described. Here's my procedure from start to finish.

Add Sta-bil and top off fuel (leave 5% room for expansion)
Run the engine until warm on muffs.
Change oil and filter
Change outdrive oil
Run engine on muffs to circulate new oil and check levels

I do not go through the trouble of pulling each individual spark plug to fog and use the latest method from Merc for the late model engines.

I use a 6' piece of fuel line, a water separating fuel filter I have designated for "winterizing" and a small container of fogging "mix". Merc tells you to mix 5 gallons which is way too much. I can do both engines on my Formula with exactly 1/2 gallon. The fogging mix recipe is:

32oz Premium fuel (non-ethanol if you can get it)
22.4oz 2-stroke oil
3.2 oz sta-bil
3.2 oz injector cleaner
3.2 oz dry gas

Remove water sep fuel filter
Install "winterizing" filter
Remove fuel line from engine
Connect 6' fuel line hose and 1/2 gallon fogging mix to engine
Start and run engine on mix at 1500 rpm for 5 minutes
Shut down engine (you should see blue smoke and notice her running rough)
R&R water sep filters
Reconnect fuel line to main tank.
Drain block of raw water (both sides) manifolds, fuel cooler (5 blue plugs) or drain via single point drain for newer 350 MAGs
Some of the newer engines with Bravo drives have blue plugs on the engine driven seawater pump. Drain these if necessary
Replace all blue plugs
Remove hoses from T-stat
Fill manifolds with antifreeze until runs out pipes or outdrive
Fill large hose until antifreeze runs out T-stat gooseneck.
Reconnect water hoses
Loosen serpentine belt
Remove batteries

11-04-2011, 11:29 AM
Pull the drive and store it until spring. There is water that lays in the drive area. This also allows you to grease everything and check your coupler, etc.

11-04-2011, 12:53 PM
My project for Saterday

11-04-2011, 01:30 PM
Winterizing (for clean fresh water boats only)

1) Fog.
2) Remove 4 drain plugs and 3 hoses.
3) Have a beer.

My last boat lasted 25 years and over 3000 hours with no major work (and still ran fine when sold)

11-04-2011, 03:01 PM

I have the same question as Ghost. I actually asked it several years ago in a thread you gave advise on about winterizing. Are we missing something?

As I see it the cold water from my garden hose is flowing through the muffs into the engine. When the engine gets hot enough the thermostat opens allowing the garden hose water to flow through the engine. As the engine remains hot and the thermostat remains open, I switch the three way valve on my winterizing kit to allow the 5 gallons of antifreeze to flow into the engine. The temp of the antifreeze is warmer then the water from the garden hose. Once I see the antifreeze exiting frm my exhaust I begin fogging the carborator. I fog until the antifreeze is about gone from the 5 gallon container, then shut her down.

Does this sound right???

11-06-2011, 04:25 PM
I did the upside down in the bilge INVERTED DOG looking for drain plugs in the block, none to be found. All other drain plugs removed. hoses pulled, I think the exhaust manifolds and block are mostly empty. My Merc book said 1-1/1/2 oz 2 stroke oil in the vapor sep. then run. I did both, oil in the sep then fog. We will see next spring. Any thoughts on HP plugs. My other go fast toys run the Platinum plugs, the 502 does burn a bit of oil, I've read this is normal?:confused:

11-08-2011, 08:47 PM
My 350 Merc has one drain plug on each side of the block.... I seem to recall reading that some brands of replacement blocks do not. Your replacement block may not...
I would question how one knows if the block water jackets really are drained???? I honestly don't know but I bet someone out there does....
The temp has only been down to 34 here on Lake Lanier, so all is good for now.
Comments or help for PMZoner??? :lookaroun:

Morgan's Cloud
11-10-2011, 10:10 AM
"the 502 does burn a bit of oil, I've read this is normal ? "


"Comments or help for PMZoner ??? "

Another of my much hated OT diversions .. Yes , when I got the 502 I was surprised to see oil consumption and sooty transoms (never experienced before) referred to as 'normal' for the 502 .

After building V8's for all these years one would have thought that GM would put out something a bit better than this if you ask me .

There was lots of convo over on OSO about this back in the early 2000's .

11-12-2011, 03:17 PM
To answer the cool antifreeze question, the antifreeze would have to be hotter than the thermostats temp setting. If you have a 140 the antifreeze must be 140 or a little better, if the antifreeze is 130 the tstat will close stopping a full fill of the block. I it is so simple to pour, it takes all the guess work out of it. Phil

11-13-2011, 03:32 PM
Phil, I think the question put another way is... If we are sucking up raw lake water all day, how does the thermostat ever open? The lake water used to cool our engines is never hotter than the thermostat setting and it somehow opens to regulate the engine temp? We know it does, so why would sucking 70 degree antifreeze from a bucket close the thermostat vs. 70 degree water from the spigot or 70 degree lake water?

11-13-2011, 05:19 PM
[ QUOTE=$originalposter]{$pagetext}[/QUOTE]

So true, another winterizing myth?

11-13-2011, 08:18 PM
[ QUOTE=Phil, I think the question put another way is... If we are sucking up raw lake water all day, how does the thermostat ever open? The lake water used to cool our engines is never hotter than the thermostat setting and it somehow opens to regulate the engine temp? We know it does, so why would sucking 70 degree antifreeze from a bucket close the thermostat vs. 70 degree water from the spigot or 70 degree lake water? [/QUOTE] Find yourself a Tstat laying around, put a piece of wire on it so you can pull it out hot put it in a pot bring the temp up until it opens. Now switch it to pot with room temp water in it, best guess about 8 seconds it will be closed. Doing the above will answer your question! Phil

11-13-2011, 09:06 PM

Help me because I must be blockheaded on this. But I still don't get it. I agree that the t-stat will do what you say in the test you describe. But that's not what happens in a motor, is it?

To make sense of what I mean, if you run the boat in a lake of 70 degree water (or 60 degree water, or 50 degree water, or whatever) all day, will the thermostat be open or closed? I assume it will be closed for a couple minutes until the engine gets up to operating temp, and then it will open. And then, once open, it will stay open, unless the engine cools below operating temp (or whatever temp trips the thermostat).

If that's the case, how could the t-stat know the difference between water and antifreeze, such that it can stay open water flowing throught the cooling system, but close with antifreeze flowing (at the exact same temperature) flowing past? It's just a bunch of liquid. Unless one type of liquid conducted heat much better than the other, it should make no difference, right? Which I checked, and it doesn't seem so.

Put another way, won't the t-stat (regardless of whether you are running in a lake ,or on muffs, or with antifreeze, or whatever) stay open once the motor heats up? And once the motor is hot, won't the t-stat stay open (with water, or antifreeze, or beer, or whatever running through it) until the engine cools down enough that such that it closes again?

Sorry for the hassle, but I'm totally lost on this.



11-14-2011, 07:16 AM
The incoming raw water does not directly hit the thermostat, it is mixed with hot circulating water before it hits the thermostat, the average temp is above what is needed to keep the stat open, that is why it stays open.

11-15-2011, 08:20 AM
somebody is going to need to draw me a diagram here .

11-16-2011, 07:29 PM
Sorry been busy!

Did not mean to get a debate going, or tell any of you how you have do it!

I gave my opinion which was formed by years of training and field experience. No question there is more than one way to skin the cat! It takes “3” gallons of antifreeze to completely fill a SBC block & Manifolds, I prefer the pour method for several reasons. Firstly I want a good fog job, making sure all internals, valves both intake and exhaust and cylinder walls are properly coated. To me the only way to do that right is to kill the engine with the fogging solution, not trying to time the end of the bucket of antifreeze and fogging. It is beneficial to have the block totally full of antifreeze; here is where the debate starts. Many will say that the Tstat will remain open when you pump cooler antifreeze through, the point missed by many is the exhaust by pass circuits that marine engines have. All stock raw cooled Tstat housings have a bypass circuit to insure full water flow to the exhaust while the Tstat is closed, if it were not for this circuit you would destroy your exhaust hoses in short order. When you suck antifreeze from a bucket it goes directly to the Tstat housing the cooler water does cool the housing and Tstat restricting “some” flow to the engine, how much from doing drain tests in tech school about ˝ gallon. ˝ gallon is probably enough not to get the heads treated with rust inhibitors, will the engine freeze “NO”!!!!!!!!!! Another point is it is proven that antifreeze tends to swell rubber impellers in school that was another reason not to suck through the pump, they said they are made for water not chemicals which shortens the impeller life. If you wish to do the pump through technique buy Globe impellers they are not harmed by the antifreeze.

In short IMO if you want to be “absolutely” sure you have done a good fog and fill job, use the pour method to removes ALL guess work. In the links below a few that agree with me and one that gives four methods, you can choose any of the four it is your engine! Today most marinas pump the antifreeze through, makes sense most flat rate winterization procedures so time is a factor to them. Boils down to do it how every you wish, I prefer to do it the best way I know how!

http://www.lakeconroemarine.net/Boat_Services/Winterize_Your_Mercruiser_Engi/winterize_your_mercruiser_engi.html (http://www.lakeconroemarine.net/Boat_Services/Winterize_Your_Mercruiser_Engi/winterize_your_mercruiser_engi.html)

http://www.doityourself.com/forum/marine-boating-sailing-pwc-nautical-navigational-gps/146226-winterizing-inboard-stern-drive-engines-updated-05-28-06-a.html (http://www.doityourself.com/forum/marine-boating-sailing-pwc-nautical-navigational-gps/146226-winterizing-inboard-stern-drive-engines-updated-05-28-06-a.html)

http://thewinterizer.com/index.php?option=com_content&view=article&id=8&Itemid=13 (http://thewinterizer.com/index.php?option=com_content&view=article&id=8&Itemid=13)

http://www.bidobee.com/winterizing-your-boat (http://www.bidobee.com/winterizing-your-boat)

11-18-2011, 08:45 AM

Not that you are, but there's no need for you to defend your process/opinion. We all know there are often times many ways to accomplish a task. We also know that many people have misconceptions on how things work and therefore use less than ideal methods. What I was asking for, and I think your latest explanation provides some very good info towards is WHY the pour method might be preferred over the "bucket-hose-muffs" method. In fact, I think we learned that it's really not because the thermostat will snap shut, but rather the water does not take a "series direct" in and out path. There is recirculating and mixing within the system and therefore an owner may need to use higher amounts of antifreeze or risk a diluted mixture with an unknown protection level.

Like you, I do, and will continue to, use the pour method you've described. It's the only way I can be confident of what is exactly in my motors when it's 0 degrees out.

11-18-2011, 09:05 AM

I am still lost on how cool antifreeze goes directly to the t stat housing????? My setup has a bypass but it is to by pass the t stat and goes into the risers any water coming to that bypass as already been thru the block. The bypass is about a 1/2 inch passage next to the t stat which lets water by this water runs to each riser

the water is sucked up from the drive into the pump then sent into the block and exits at the t stat housing . in one pic you can see the water connection for the output of the pump it is sent into the block on both sides thru the front plate. in the other pic you see the bypass from the t stat housing into the risers.

am I missing something?

if you run and recapture the antifreeze is quite warm after a few minutes and you can fog under no pressure , it also lets you know that the t stat is open and the antifreeze is all thru the block. I don't worry about what the antifreeze does to the impellor cause after that the entire system is drained. this way the oil is warm too so it makes it easier to pump out.

11-18-2011, 04:46 PM
Matt you are right as to how cross overs will fill better, they feed direct into the block, stock Tstats allow the cooler water to cool the housing and Tstat. The result is water comes out of the exhaust before the block is filled completely. The biggest majority of boats have stock Tstats with exhaust bypass.


11-18-2011, 05:09 PM
Got ya Phil. Every setup is a bit different. I was thinking the pour method might be a little difficult on a ford setup the t stat opening is vertical not horizontal like a Chevy. A few ways to do this everyone needs to find the right method for their setup

11-18-2011, 08:52 PM
Quote: Pismo

The incoming raw water does not directly hit the thermostat, it is mixed with hot circulating water before it hits the thermostat, the average temp is above what is needed to keep the stat open, that is why it stays open.

My question would be how long would it take to fill the block high enough to get circulation, remember you are filling a drained block with -0- water!

11-20-2011, 08:32 PM
I am on a boat lift on Lake Washington. No matter how many hours I put on the boat during the season I always go through this drill when winter comes. This is a raw water cooled AQ 260 Volvo-Penta 1985 motor installed in a 1970 Sweet 16. Heat it up, suck the oil out, change the oil and oil filter, put green Stabil into the gas, run the engine up, fog it out to near stall, turn it off, drain both sides of the block and each of the headers, close the drains, open up the starboard hose leading to the waterpump, pour about a quart of el-cheapo antifreeze into this, close it up, drain the dicarded water out of the bilge, Check the battery levels, connect up the Deltran battery tender, connect up the Gold rod heater tube, install a 60 watt light bulb connected through a connector that does not let power through unless freezing, give the whole system a pat on the deck, cover with the tonneau, let it rest under my Sunbrella covered boat lift and look to waking it up in the spring. I installed the Duoprop conversion, but leave it alone as this is fresh water and about 4 hours per year usage.

10-15-2012, 12:21 AM
I have a new boat (for me) and am confused about what I have read in this string. I have 6 gallons of RV antifreeze, a 5 gallon boat oriented container, a hose and muffs. I am planning to put red Stabil in the gas tank, run the engine until hot, change the oil and oil filter and run the engine until hot again. Then I plan to hook up the muffs, connect the hose to the 5 gallon container with the RV antifreeze in it and run this until almost empty and them fog out the engine with a spray can of fogging oil. This new boat for me has all kinds of stuff my previous boat did not have. I am concerned about whether I should be doing more than what I did with my previous AQ 260A, which was in a 16 foot boat. The new boat is a 18 foot with a modified Mercruiser 454 c.i. engine in it. It has stuff like Gil Select Sound mufflers, Latham steering with a full hydraulic helm, a sea strainer, etc. I am concerned just draining the block like I used to in the old boat is not going to work here. I was planning to run the RV fluid through the system and figured that this would cover all the unknowns about various coolers, etc., that I am not familiar with. What suggestions can I receive here?

10-17-2012, 04:56 PM
...or you can (if in clean fresh water)
1- put stabil in the gas sometime during your last tank
2- fog while putting the boat on the trailer
3- remove 4 plugs and 4 hoses and you are done, make sure they flow

5-10 minutes tops

This will yield the exact same results over 30 years as any other method.

Scott Pearson
10-17-2012, 06:37 PM
Just don't run a thermostat! Then no need to worry at all!

10-17-2012, 09:44 PM
[ QUOTE=$originalposter]{$pagetext}[/QUOTE]
I can envision two plugs on each side of the block and two plugs on the headers. Which four hoses should I focus on? By the way two us on board and a fairly full tank of gas pulled 82 MPH on the GPS this evening on Lake Washington (this is an 1988 18 foot with a 454 c.i. Mercruiser 420 in it).


Dr. David Fleming
10-20-2012, 07:07 PM
The thermostat in the automotive engine is a temperature regulating device. The engine cools and circulates the coolant with the thermostat closed. When the thermostat opens the radiator or lake water is admitted into the engine cooling jackets. The thermostat opens and shuts to keep the temp at a constant level. Circulation through the radiator or from the lake is not necessary to cool the engine.

Winterizing the engine is designed to get the coolant changed in the engine. Merc service says to remove the thermostat unless you can trick it into staying open to flush the system.

Go figure.

10-21-2012, 10:32 AM
Interesting thread. I follow the procedure from a Clymer shop manual. My 350 MAG EFI has a plug on either side of the block, one on each manifold, and one on the fuel cooler, five total. My power steering cooler has no plug. Manual says pull the hose off, but I have never had water in it after opening the other drains. Manual also says to pull the hose from the engine circulating pump - that does drain additional water.


Dr. David Fleming
10-27-2012, 11:13 AM
Maybe this is the last shot at this thread but it came to me that I read about Smokey Yunick in his tuning of the BBC was working on any performance issues related to the water coolant flow in the race engine. Apparently the basic coolant flow design was worked out years ago when GM designed the engine with little evaluation of the design after that. Smokey found that the two cylinder heads fought over the coolant and this lead one bank of cylinders or the other to run hot. By changing the flow he was able to achieve much better engine performance from the BBC. I think he also concluded that for automotive racing it was best to just toss the thermostat.

Interestingly enough my curiosity on this started when I examined Mercury Racing coolant flow design in the 500 EFI engine which uses a different style thermostat housing and a couple of heater hoses with check valves going into the CMI headers. The MerCruser 454/502 MAG MPI does not use this type of coolant flow design. Apparently the 500 EFI was design was attempting to address the same coolant overheating issues Smokey was.

I assume when the thermostat gets hot enough it will open regardless of the temperature of the incoming water - that block gets hot and so does the water then its open baby!. The kitchen stove water test has been pretty standard for thermostats. I have also seen a weird assortment of thermostats that seem to have very restricted water flow capability yet parts guys insist they are the direct replacements for much more open thermostats. Most all work by an internal wax pellet, years ago they worked with a soldered brass bellows. There is little or no discussion of any of this to my knowledge.