Questions about cooling, heat exchanger, and antifreeze

[and4ew]

When my new-to-me boat was hauled out in 2019 I asked the yard to winterize the engine because I couldn't be there (I live far, far away) the engine is Yanmar 2gm20F and it's my first diesel. After waiting out covid I'm back at that boat. When I changed the impeller there was anti freeze in the line and maybe a 1/2 cup or so spilled when I took the hose off. This started me thinking and led to these questions:
- raw water comes in throught the through hull, to the strainer, then to the water pump, and then to the heat exchanger and then out the mixing elbow then back out through the exhaust through hull, right?
- to winterize the manual I have says that water should be drained out and antifreeze added. How/where was water drained out and antifreeze put in?
- what circulates the fresh water in the engine block, is there another pump?
- is the engine block water actually antifreeze (like in a car) i.e. its not water at all; its antifreeze, and if so is it the same type of antifreeze that gets used in the raw-water system?

[Sailmonkey]

Point 1. Correct

Point 2. Easier to just run the engine with the seawater suction line in a bucket or jug of antifreeze

Point 3. There is another pump, just like any other water cooled engine, driven by the alternator belt

Point 4. Correct, just like a car.

[tkeithlu]

Addendum to #4:

Not only antifreeze. Usually a 50-50 mixture of antifreeze and water. The antifreeze lowers the freezing point, raises the boiling point, and supplies rust inhibitors. The water is there because there is no better liquid on earth for heat absorption and transfer.

[Sailmonkey]

Originally Posted by tkeithlu

Addendum to #4:

Not only antifreeze. Usually a 50-50 mixture of antifreeze and water. The antifreeze lowers the freezing point, raises the boiling point, and supplies rust inhibitors. The water is there because there is no better liquid on earth for heat absorption and transfer.

For further clarification. The auto parts store will stock different types of coolants, some mixed, some concentrate, not all are compatible with each other.

So…..tread carefully here, don’t mix types, and never add straight/undiluted concentrate coolant to the engine.

[Midnight Son]

Originally Posted by tkeithlu

Addendum to #4:

Not only antifreeze. Usually a 50-50 mixture of antifreeze and water. The antifreeze lowers the freezing point, raises the boiling point, and supplies rust inhibitors. The water is there because there is no better liquid on earth for heat absorption and transfer.

FYI

With anti-freeze a much greater than 50/50 ie ~65/35 results in less heat transfer. It freezes at a much lower temperature (never seen in a marine environment) but is not as good at removing heat. Cooling systems are designed for 50/50 mix. Also use diesel rated anti-freeze, as it has anti-cavitation additives. Replace coolant annually for longest cylinder/liner service life, unless there is a coolant filter (larger engines), which is to be replaced annually.

[captstu]

Yanmar 2GM diesels are made in two (or more) variants. If the engine is raw water cooled, a single belt drives a single pump on the bottom of the engine - then the belt drives the alternator an back to the engine.

This pump circulates the raw water through the heat exchanger, into the engine, back out thru the same heat exchange but another path and into the mixing elbow (smaller pipe) where it is mixed and cools the hot exhaust gas.

It is critically important that the mixing elbow be inspected or better out every 700 engine hours or you will damage the engine's head gasket.

On a fresh water cooled engine, a second pump located below and in front of the first pump is driven by a second smaller belt. It picks up raw water, pumps it thru the heat exchanger and into the same exhaust elbow with the same restriction on 700 hour replacement.

The pump mentioned above now circulates the water/antifreeze mix thru the pump, the fresh water side of the heat exchanger and the block.

When winterizing, a raw water cooled engine normally is winterized by closing the inlet thru-hull and pouring a steady stream of 50/50 antifreeze/distilled mix until it comes out of the exhaust.

The same process is followed on a fresh water cooled engine except I always recommend the water/antifreeze circuit be drained and fresh water/antifreeze be put in. I save the drained water/antifreeze mix in a glass bottle to see if any oil is observed on top of the mix removed before recycling it as hazardous waste.

In either case a 50/50 mix of antifreeze/water remains in both pumps to protect them, especially the raw water pump that must be kept wet to protect the blades from sticking to the interior of the pump.

Some service shops loosen the screws on the raw water pump so the impeller can easily be changed in the Spring. This leaves the raw water pump in a non-working position and if the owner neglects to change the impeller serious damage may result.

[jlblan2]

If your Engine cooling fresh water is being circulated through your water heater heat exchanger, remember not to use an antifreeze that is poisonous. If you get a pin hole leak in that exchanger, you may not come back from the trip. There are RV antifreezes that are not poisonous.

[Lepke]

Originally Posted by Midnight Son

FYI

With anti-freeze a much greater than 50/50 ie ~65/35 results in less heat transfer.

I learned this the hard way as a kid. I used 100% anti-freeze in a PU that I used in zero F weather. It worked fine in the winter, but come summer, driving on a hwy, it quickly over heated, blew a hose and was so hot the gas engine wouldn't stop, it just dieseled. I had to stall it out. Later I did a complete rebuild.

[Dsanduril]

Originally Posted by jlblan2

If your Engine cooling fresh water is being circulated through your water heater heat exchanger, remember not to use an antifreeze that is poisonous. If you get a pin hole leak in that exchanger, you may not come back from the trip. There are RV antifreezes that are not poisonous.

If you're going down that road, make sure to understand the difference between "antifreeze" and "coolant". Many/most of the "RV antifreezes" are not intended for use as an engine coolant and say so on the labels. There are non/low-toxicity coolants, for operation in the engine (as opposed to winterizing) make sure you get a coolant product.

[kaisardog]

Yanmars recommend the *reen stuff’ ie dextron antifreeze. It is used in the freshwater (radiator tank) UNDILUTED. Diluting antifreeze Makes no sense and jn our -30 degree temps could be a problem and split your metal components apart. Some locals here on the great lakes suck pure not diluted antifreeze in thru their raw water pump which on the yans is driven off the engine. Some use the ‘pink stuff’ drinkable water system antifreeze which says it s tested to -30 degress. I can tell you pink stuff potable water system is not good to 30 below because i have now seen 3 isotemp stainless hot water heater tanks split apart by freeze damage at the elliptical gasket because the pink antifreeze turned into slush in the tank and owner didnt drain the antifreeze out . Dont trust antifreeze labels in the far north, it freezes at far higher temps than the -30 degree they claim on the label. Draining the Cooling system removing the plug on the block is recommended. Filling your yanmar with pink stuff or green stuff and leaving it in the cooling passages all winter is not. That being said lots of boats here on the great lakes do the pink stuff antifreeze , leave it in all winter, and have fine and undamaged engines come spring.

[Midnight Son]

50/50 solution turns to slush at -35°C, never had an issue at -45°C.
Do as you see fit.