Confused about winterizing the Universal M25 5421 engine

[jen1722terry]

Hi fellow owners,

Last year was our first with our CD 31, and we had the yard do the engine winterization.

This year, we would like to winterize the engine ourselves, but we're confused.

Many posts indicate that the engine should be warmed up, flushed with fresh water in the raw water system, then filled with
antifreeze. However, the Universal owners manual gives two options for winterizing the engine:

1. for boats on the hard, simply drain water pump, manifold, heat exchanger and muffler, then close the seacock. Replace heat exchanger zinc.

2. for boats in the water or on the hard, warm up the engine, put the inlet hose in a bucket of antifreeze and crank engine until the exhaust is pink (being careful to drain the muffler before and after this is done).

My question is: Is one option preferable to the other?

Also, do we have to remove the thermostat for either procedure? If so, how is this done?

FYI: the boat will winter in coastal Nova Scotia. Cold, but rarely below zero.

Thanks in advance for the kind advice,

Jenn and Terry McAdams

[Mike Davis]

Dear Jenn and Terry,
I have the same engine and winterized it today using the red antifreeze in the bucket method. I did it at the working dock of my marina, therefore, I don't have to start the engine tomorrow when it is hauled for the season. When I saw the antifreeze coming out of the exhaust a let it run a bit longer then shut down the engine . I do this every season. I also drain my 3 fresh water tanks and use antifreeze in them. It's a very simple winterization.

[Steve Laume]

On Raven, which stays in the water for the winter, I warm up the engine, then take the top off of the sea water strainer, close the seacock and pour a gallon of pink into the strainer while the engine is running. I have never drained the muffler as it would only have antifreeze in it at this point. I have never messed with the thermostat either as that is in the fresh water side of the system. I have been doing it this way for years and some times several times a year when we go out for mid winter seal trips.

If you don't have a seawater strainer then just take off the intake hose and stick it in the jug or use a funnel and pour it in. Winterizing the engine isn't all that hard, Steve.

[Maine_Buzzard]

Thermostat stays in, unless you are changing the antifreeze on a boat with a heat exchanger.

Yours is "Fresh water cooled"? With a radiator cap on a tank on the engine and green antifreeze under it? Drain the antifreeze according to the engine manual and clean out the heat exchanger by boiling it stovetop in vinegar. This is not a seasonal event, usually on a 2 year schedule.

Mine was just starting to clog up after the PO had gone 5+ years without cleaning it.

This is a great task to learn after mastering oil changes and impeller service.

The heat exchanger is your marine radiator, flowing raw cold salt water through 30 or so straw sized pipes while hot antifreeze passes over the stack of pipes. To me, it looks like a handheld nuclear power plant...

The thermostat can easily be swapped at this time. It's usually at the top front of the engine, held on by two or three bolts. The housing has a hose running to the heat exchanger. Remove the bolts, wiggle the housing, and it will break free. You may have a gasket along with a rubber ring around the thermostat. Assembly is simple, if you took a picture of it while taking it apart. Usually, you are prevented from putting it in backwards. The spring and copper cylinder go on the hot engine side, not into the housing.

Preventive swapping the thermostat is a conundrum for me. If it's not broken or corroded, I trust it as much as a new one. I tend to keep it in as long as possible.

Draining antifreeze every few years will do more to help than anything else.

Of course, if it's important, MaineSail has a great page about it.

http://www.pbase.com/mainecruising/heat ... ger&page=1

[Neil Gordon]

Preventive swapping the thermostat is a conundrum for me. If it's not broken or corroded, I trust it as much as a new one. I tend to keep it in as long as possible.

There's some conventional wisdom that suggests you install the spare, keeping the original as the backup. You'll find out quick enough if the installed spare is working according to spec (if it works at all) and if/when it fails, you know you have a replacement that both fits and works.

[jen1722terry]

Thanks so much to all of you for the kind advice.

Winterization went pretty well. We were puzzled at first by the very slow uptake of fresh water and antifreeze from the bucket at low rpm. Odd, for the engine was spitting out lots of water from the exhaust during warmup before we closed the seacock and put the raw water intake hose in the bucket. We eventually figured out that nudging up the throttle corrected the problem and the fresh water rinse and then antifreezing went smoothly. We're guessing we need a new impeller, for ours, on examination, had some cracked vanes.

But now we're wondering if the engine is getting enough cooling at low rpms. Could it be a partially clogged heat exchanger? We doubt it was the thermostat, for the engine was warm and operating well within temp limits.

Thanks to Maine Buzzard for the tip on boiling the heat exchanger every few years. Questions: how long to we boil it? Also, would the boiling damage the paint on the exchanger (not that the paint is all that nice, the engine is due for repainting this winter)?

And thanks also to Neil for the tip on testing a new thermostat. This is already on our "to-do" list for spring outfitting.

Well, today we're beginning to wonder if the yard can get our 31 on the hard before the hurricane heads up this way. Current track has the storm well east of us, but we all know hurricanes. We'll see.

Back to chores up here in sunny Mahone Bay, Nova Scotia!

Jenn and Terry

[M. R. Bober]

The "slow uptake" from the bucket (as compared to the normal flow) could be a worn seawater pump or impeller, but I doubt it. When the boat is in the water and the engine seawater seacock is opened, the sea is being forced up the hose (the through-hull is a foot or two below the water line.) When drawing from the bucket, the pump is doing all of the lifting.

Keep an eye on your temperature gauge. I doubt you'll be running hot at low rpm.

My $0.02>>>I would never leave the cooling system dry as I would worry about rust. Drain & refill with anti-freeze.

Mitchell Bober
Sunny Lancaster, (Where winter is only a visitor.) VA

[JWSutcliffe]

A word of caution: removing the thermostat in the M25 unless it is really necessary is an invitation to spend hours solving a non existent problem. Replacing the thermostat regularly is not a bad idea with a raw water cooled engine (i.e. one with no fresh water loop) because the thermostat is always exposed to salt water and prone to salt deposition. However, with the fresh water cooling in a 31 like you have, it is not typical practice to change out the thermostat unless you are experiencing overheating, which may be a symptom of thermostat problems. After all, how often do you have the thermostat changed in your car? Rate of uptake of antifreeze by the raw water pump has nothing to do with thermostat operation. The raw water pump is on the raw water loop - the thermostat is on the completely separate fresh water loop.

The reason for my note of caution is that the fresh water cooling loop of the M25 is very, very hard to bleed of air after it is opened up. Unlike in an automotive cooling system, the CD31 has the added complexity of the water heater and its associated volume of hoses, fittings, etc. Having gone through this exercise several times now to remove or replace, at various times, the heat exchanger and exhaust manifold flange, it is a long and drawn out affair to iteratively run the engine to the point of overheating, shut down, let the trapped air "burp" out from the opened header tank and thermostat housing bleed valve, add coolant, and repeat.

[Maine_Buzzard]

Agreed on bleeding antifreeze circuits with a water heater. It depends on where the high point is in the system, correct? The heater must be lower than the radiator cap, and the lines will need to be angled correctly to fill and drain... Any sways will trap air.

JW, what caused the HX failure?

Still, it needs to be done every few years. Looking at an eight year old antifreeze clogged system is no fun. I'll suggest that if you can't remember when it was last changed, it's time.

My HX is a bit different from the M25, in that it has a removable core about the size of a soda can and it can easily fit in a pan. I boiled mine for about 30 min in pure vinegar. CLR or similar will also take out the scale, probably not as well.

For an integral HX, follow Rod's advice and pull the HX and have a radiator shop solvent clean it. They can repaint and return it shiny clean one for an easier solution.

Any missing impeller vanes? You really should pull the HX and look for the bits. They will be at the end where the cold raw water hose feeds in.

All of this could be done in the spring, prior to launch. I suspect leaving the antifreeze in place for the winter is better than draining and leaving holes in the engine.

[JWSutcliffe]

My heat exchanger was the 25 year old 2 inch original, which was undersized for the M25 and prone to overheating above 2100 rpm even without the years of scale buildup. Since Universal had recommended upgrading to the 3 inch heat exchanger, I opted for that instead of trying to refurbish the old unit. It was a worthwhile upgrade.

[jen1722terry]

Thanks, belatedly, for the advice on the HX on the MD25. Our engine also starts to heat up a bit over 2200 rpm. It's not a major problem yet, as she does about 6.5 knots at 2150, which is fine with us. But your insight has us now thinking that a new HX should be part of the winter purchases (we spend half the year here in Nova Scotia, where we avoid buying anything pricey due to the higher prices as 15% sales tax - we go home mid-December).

Question: any major problems installing the new 3" HX? Or is it pretty much an easy swap?

Our 31 is now on the hard, as we prepare to rip out the old water heater. The new one is on the way from Defender, as is the rebuild kit for the Whale waste water pump. Those chores and other odd jobs should fill up our spare time before we head back to New Hampshire in December.

Looking forward to your advice, and thanks again for the help.

Jenn and Terry

[JWSutcliffe]

No real problems doing the swap. The only down side is that unlike with the 2 inch heat exchanger, after installing the 3 inch heat exchanger the transmission dip stick cannot be removed without first loosening the HX attachment hose clamps and moving the entire HX back an inch or so. However, this is only something we do once a season, so not a big deal.

[Steve Laume]

Raven is a CD-30 with Universal engine and I always had to loosen the heat exchanger to get at the zinc. I solved the problem by moving the heat exchanger onto a bracket, glassed into the hull,aft of the transmission. Actually it is mounted onto a shelf I already added to hold the hot water heater. It is a very simple little saddle with a couple of hose clamps to hold it in place.

If I was going to be changing my heat exchanger, I would definitely not put it back in the original position. It is much easier to get out now and it kind of unclutters things back by the transmission, Steve.