Diesel Engines with direct raw water cooling

[Captain Graham]

Hello All,

I live in the Cleveland OH area and looking for an 27-32 ft sailboat.
Most of the older sailboats I am looking at have direct raw water cooling for their Diesel Engines.
No heat exchanger the raw water is pumped into the engine block just going thru a raw water strainer.

The two sailboat I am thinking about have the following
Boat1 has a Yanmar 3GM30.
Boat2 has a Universal M25.

Questions
1. Should I be concerned with the engine block developing build up and then overheating?
2. Is there a way to clean out any build up in the engine block?
3. Is there a heat exchanger kit that I can install?
4. This there any other issues with this cooling system?

[sailormed]

Freshwater or seawater navigation?
2. You can clean cooling circuits with "barnacle buster" or similar products.
4. Engines with this system run at lower operating temperature because above 65°C (not sure) you get salt depots in the circuits for seawater cooling.

[Captain Graham]

Originally Posted by sailormed

Freshwater or seawater navigation?
2. You can clean cooling circuits with "barnacle buster" or similar products.
4. Engines with this system run at lower operating temperature because above 65°C (not sure) you get salt depots in the circuits for seawater cooling.

The boats I am looking at are in Lake Erie but I have not asked if they have ever been in salt water.

In my case I will be sailing in freshwater.

[sailormed]

Sorry Cleveland OH area did not ring a bell with me, living across the pond.

[Captain Graham]

Originally Posted by sailormed

Sorry Cleveland OH area did not ring a bell with me, living across the pond.

Not a problem.

[Wotname]

Originally Posted by Captain Graham

Hello All,

I live in the Cleveland OH area and looking for an 27-32 ft sailboat.
Most of the older sailboats I am looking at have direct raw water cooling for their Diesel Engines.
No heat exchanger the raw water is pumped into the engine block just going thru a raw water strainer.

The two sailboat I am thinking about have the following
Boat1 has a Yanmar 3GM30.
Boat2 has a Universal M25.

Questions
1. Should I be concerned with the engine block developing build up and then overheating?
2. Is there a way to clean out any build up in the engine block?
3. Is there a heat exchanger kit that I can install?
4. This there any other issues with this cooling system?

I can't speak to the M25 but the following applies to 3GM30. FWIW, I have owned four Yanmar engines with direct raw water cooling.

The engine has been designed from the get go for raw salt water cooling e.g. they have a different (cooler) thermostat and anodes in the block and head. With proper maintenance, they last a very long time (many decades).

It is important the anodes are checked regularly (say yearly) and replaced as required.

The engine can be de-scaled in situ without too much effort. There are various products available but vinegar will work for light scaling and muriatic (hydrochloric) acid will remove the most stubborn scaling. The commercial products fall somewhere between these two extreme acids.

Engines routinely operated in freshwater areas should present zero issues although the anodes still need checking.

[Wotname]

The method I use for descaling is as follows.

Remove the anodes and refit the capping plugs.
Plug the head bypass hose (between the water pump and thermostat housing)
Rig a temporary hose into the bottom of the block (where the water pump hose usually goes) and another temporary hose from where the discharge water exits the engine.
Fill a bucket with descaling fluid of choice and use a small pump (say a small bite pump) and circulate the fluid though the engine via the temporary hoses.

If using a mild descaling fluid (like vinegar) let it circulate for say 24 hours but if say muriatic acid (around 20%), then 30 minutes should do it.

Drain and rinse with fresh water and then replace the anodes (with new ones), remove the bypass plug and refit original hoses.

[Compass790]

I wouldnt bother about fitting a heat exchanger if you are going to use in fresh water.
We have a 1980 raw -water cooled Yanmar that has lived in the sea all its life & has minimal corrosion. As Wotname said just keep up the anodes tho freshwater are meant to be magnesium.
I would be tempted to try a higher temp thermostat if it was fresh water use only but I doubt that Yanmar makes one. That would be a homemade project.
Only reason I'd want to do that is more fuel efficiency & higher oil temps.
Ours only reaches a temp of 59oC max oil temp. I like to fiddle with things & improve them but not necessary to do.
The conventional wisdom is that its better to have higher engine temps than raw water cooled run at 60oC max but I'd be more worried about engine condition than cooling system when buying a fresh water boat.
The Universal which I believe is Kubota based will have a lot cheaper parts if you buy from Kubota.
Hope that helps.
Wots a bite pump Wottie?

[Wotname]

Originally Posted by Compass790

.........
Wots a bite pump Wottie?

It's an age related tipo thingie...

You youngsters might say it is a typo for bilge pump .

[Captain Graham]

Thank guys I think you are right.
If the motor is in good shape after all these years then I will just do a simple flush.

I have watched a few youtube videos (so now I am an expert LOL) and I think I will just do a reverse flow vinegar flush.
The reason for the reverse flow is to flush out chucks of stuff that may have been sucked into the engine.
Some of the videos showed parts of an old impeller getting flushed out this way.

Thanks again to both Wotname and Compass790.

[Wotname]

Originally Posted by Captain Graham

Thank guys I think you are right.
If the motor is in good shape after all these years then I will just do a simple flush.

I have watched a few youtube videos (so now I am an expert LOL) and I think I will just do a reverse flow vinegar flush.
The reason for the reverse flow is to flush out chucks of stuff that may have been sucked into the engine.
Some of the videos showed parts of an old impeller getting flushed out this way.

Thanks again to both Wotname and Compass790.

I dunno what YouTubes you have seen but do make sure you remove the anodes, thermostat and block the bypass hose. Failure to do so will result in tears .

[Captain Graham]

Originally Posted by Wotname

I dunno what YouTubes you have seen but do make sure you remove the anodes, thermostat and block the bypass hose. Failure to do so will result in tears .

Thanks for the added points.

Here is one of the videos I watched

https://www.youtube.com/watch?v=ydkpgCiL2Rg

[Compass790]

Originally Posted by Captain Graham

Thank guys I think you are right.
If the motor is in good shape after all these years then I will just do a simple flush.

I have watched a few youtube videos (so now I am an expert LOL) and I think I will just do a reverse flow vinegar flush.
The reason for the reverse flow is to flush out chucks of stuff that may have been sucked into the engine.
Some of the videos showed parts of an old impeller getting flushed out this way.

Thanks again to both Wotname and Compass790.

Another good thing to do is fit a strainer after the raw water pump to prevent impeller pieces going into the engine cooling galleries. Impeller pieces are more of a problem in salt water as they cause localised hot spots & the salts precipitate out & can close the gallery completely
You can by them for peanuts online. I had to drill some bigger holes in the ss mesh in ours as little jellyfish & eggs blocked it. Also had to thread tape it a bit but for the price it works good
https://www.aliexpress.com/item/3284...27424c4dFkKLKW
Just an example, I'm sure you can find them on fleabay or big river

[Kumbaya31]

I have a Universal M25 and it has a heat exchanger. I thought that was part of the package. Are you sure it's an M25 and are you sure there's no heat exchanger?

[CarinaPDX]

The Yanmar was designed for seawater cooling - Yanmar is an old manufacturer of engines designed for marine use. (Today's Yanmar engines are designed as utility engines with an eye to marinizing, which is a different thing.) The Universal being a Kubota was probably not designed for seawater use, and I would be reluctant to use it in salt water. I see no reason to not use any diesel in fresh water without a heat exchanger (but I haven't really studied the problem).

My old Sabb engine was seawater cooled, and after a few years flakes of minerals that had accumulated inside the cooling channels would break off and occasionally block the flow in the small (3/8") channel from the head to the exhaust manifold. There was a threaded plug beside it so it was easy to clear with a coat hanger. Of course the random overheating of the engine was less than amusing. In retrospect I should have been flushing it with acid.

Speaking of acid, a post mentioned muriatic acid. Muriatic acid is just another name for hydrochloric acid. But there are big differences in strengths; in Europe it is highly diluted, but in the US it is generally stronger. I used the European version to keep the head plumbing clear of scale, but the US version needs to be diluted for that application. I'm sorry I don't remember the actual strengths but I do remember that they are quite different.

Greg