Coolant overflow expansion tank for sailboat diesel engine

[ErikFinn]

I have a Beneteau Oceanis 430 with a Perkins Prima M50 diesel engine and the setup did not come with a coolant overflow expansion tank from the factory, the possible overflow is led through a hose from the coolant header tank filler neck (Heat exchanger/manifold/header tank assembly), under the filler cap, to the pan under the engine.

Is it very common for similar boats NOT to have a coolant expansion tank? Or is mine uncommon?

If I wanted to install one, say just buy an expansion tank for a car and install that, what would be the correct position? On engine centerline and somewhat above the engine?

Erik

[never monday]

it is a very common installation.
Yes, A car overflow tank will work. I'd mount it as close to level with the cap as possible.

[gts1544]

ErikFinn, We recently installed a coolant expansion tank on our Beneteau, but were not told about the necessity of getting a different "radiator cap" that would allow the coolant to be sucked back into the system as the engine cools.

[thinwater]

FYI

The purpose of expansion tank is not to save coolant but rather to exclude oxygen from the cooling system. Less oxygen, less corrosion. Thus, they have become common practice. However, as noted, pressure cap must be matched. The location won't matter too much, but level with the cap is best.

(I manufacture engine coolants and am on several standards committees.)

[ErikFinn]

Originally Posted by never monday

it is a very common installation.
Yes, A car overflow tank will work. I'd mount it as close to level with the cap as possible.

Thanks never monday,
do you reckon about 20cm (10inch) above the cap would be a bad idea? Because that's where I would have free space where to put the tank...

Originally Posted by gts1544

ErikFinn, We recently installed a coolant expansion tank on our Beneteau, but were not told about the necessity of getting a different "radiator cap" that would allow the coolant to be sucked back into the system as the engine cools.

Thanks gts1544,
good to know. Would the correct cap then be similar to that what cars use?

Originally Posted by thinwater

FYI

The purpose of expansion tank is not to save coolant but rather to exclude oxygen from the cooling system. Less oxygen, less corrosion. Thus, they have become common practice. However, as noted, pressure cap must be matched. The location won't matter too much, but level with the cap is best.

(I manufacture engine coolants and am on several standards committees.)

Thanks thinwater,
I didn't know that, excellent info! IF an expansion tank was installed, the pressure cap for the coolant header tank (Heat exchanger/manifold/header tank assembly)would then be similar to what cars have? If the tank was about 20cm (10inch) above the cap would that be a bad idea?

Regards,

Erik

[roverhi]

Does the coolant expansion tank have a tube in the cap that goes to the bottom of the tank??? The PO installed the tank so I almost always would hit the hose to the engine and knock the cap off when doing anything around the engine. I don't remember if there was was a tube in the cap. There certainly is none now.

I've since rerouted the hose and made a different bracket so the hose isn't so vulnerable.

[hellosailor]

Erik-
"just buy an expansion tank for a car and install that,"
I would note that this is a perfect opportunity for some recycling. Pretty much any container that is a size convenient to the location will do. A two liter soda bottle, a plastic detergent bottle, there are plenty of heavy duty plastic bottles that most of us toss out every week, that will do just as nicely as whatever you can find in the auto stores. And the pickings in the auto stores may be pretty slim, giving you few options for size and fit.
Just fwiw.

[HappyMdRSailor]

Confirming others opinions.... Any tidy auto tank, I like above the cap, but that's just me... replace w/ auto cap... 12PSI???

[David M]

Tank above the engine, so any air in the cooling system eventually bleeds out.

[Stu Jackson]

Just buy a small Rubbermaid container, the hole in the top fits the 1/2" hose almost perfectly.

[dannobee]

Any kind of recovery/overflow tank will work as long as the tube draws coolant from the bottom of the recovery tank.

Like said above, you may need a different "radiator cap." If you take off the cap, look under the cap. There should be a small disc in the center. If you wiggle the disc with a pencil or something similar, you'll see that there is a rubber gasket underneath. This check valve is necessary to suck the coolant back up from the recovery tank.

FWIW, air will be purged out when the engine is at operating temperature, and will suck the coolant from the recovery bottle as the engine cools down. It will likely take a few operating cycles to purge all of the air from the system, and you will now check the coolant level at the recovery tank instead of removing the cap and peeking down.

Height of the recovery tank isn't relevant; mount it anywhere convenient. If you do mount it above the level of the cap, then remove the cap for any reason, the hose will siphon all of the coolant out of the recovery tank, making a big mess, so watch for that.

[MarkSF]

Originally Posted by thinwater

FYI

The purpose of expansion tank is not to save coolant but rather to exclude oxygen from the cooling system. Less oxygen, less corrosion. Thus, they have become common practice. However, as noted, pressure cap must be matched. The location won't matter too much, but level with the cap is best.

(I manufacture engine coolants and am on several standards committees.)

I believe it became particularly important when Dexcool was introduced - it worked well in a cooling system with no air present, but resulted in terrible corrosion and crusty deposits if it was.

[mrm]

Originally Posted by hellosailor

I would note that this is a perfect opportunity for some recycling. Pretty much any container that is a size convenient to the location will do...

While I agree on recycling idea, I would recommend some caution in a container choice. My idea would be to visit a nearest car wreckers yard and pick a coolant expansion tank designed for the job.

One more thing for consideration. As I understand, the original system was basically unpressurized, with only an overflow tube to the open air. It seems, that the idea is to convert it to a pressurized cooling system. Are all parts of a currently installed cooling system designed to work with pressure in the system? Is heat exchanger up to it?

Finally, modern designs have two pressure hoses connecting the tank to the rest of a cooling system. One slightly bigger (supply), teed to some low place in the cooling loop, another one smaller (return), teed to the highest possible place in a cooling loop and connected to the top/side of an expansion tank. This way air is purged very fast from the system but the side effect is that some coolant is always circulated through the tank. So the tank sees the same coolant temperatures as the rest of the system.

Marius

[hellosailor]

Two hoses really sounds like someone's nephew has a hose factory. When hot antifreeze spews into the bottom of a cold recovery bottle, it will circulate and mix, so there will be enough circulation with half the plumbing.

Dexcool, Halvoline, the new "permanent" red or orange antifreezes, need to be used with some caution. They are not totally compatible with all engine seals and they are especially incompatible with some of the old green/blue antifreezes. The big trick, one you filter out the internet noise, seems to be that the old antifreeze needs to be drained and rinsed from the block before using the new, so it is replaced not mixed.

Assuming the stash of a/f is probably the same as what's in the engine...I'd just use it up and worry about converting when this runs out. A can of "water pump lubricant" replaces the additives that do wear out in a/f, and a simple a/f tester can tell you if what's in there is still good to prevent freezing. Looks & works just like a hydrometer.

[mrm]

Originally Posted by hellosailor

Two hoses really sounds like someone's nephew has a hose factory. When hot antifreeze spews into the bottom of a cold recovery bottle, it will circulate and mix, so there will be enough circulation with half the plumbing.

You missed the point completely.

Two hoses is not about circulation, it is about bleeding air from the circuit fast. Resulting circulation is just a byproduct (useful though, for example when adding antifreeze concentrate).

Study this drawing if you like: 12v Pages - The Engine - Component Locations

You will find this design under the hood of most cars, at least in Europe.