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**skipmac** · 28-04-2019, 19:15

Actually this isn't exactly correct. The boat came with a coolant overflow tank but I had to remove it from the system as part of a plumbing nightmare but left the tank there.

So now years later I want to reconnect the overflow tank but where to hook it into the cooling system? Yes I know the fresh water, not raw water side but where? I know in my car the overflow comes out of a small hose just under the radiator cap but doesn't look like this is an option on the boat. There are two hose connections coming off the back of the cooling water tank that used to run to a hot water heater. Would I just run a hose from one of those to the remote overflow tank?

captstu · 28-04-2019, 19:34

I just finished this on my boat’s Yanmar 4BY2.

Photos on Shearwater-sailing.com

**skipmac** · 28-04-2019, 20:07

Quote:

Originally Posted by captstu

I just finished this on my boat’s Yanmar 4BY2.

Photos on Shearwater-sailing.com

Hi Stu,

Thanks for the reply. I saw two photos in the section Solving the Shearwater Cooling Problem but I couldn't see where the hose from that nice stainless overflow tank connected back to the engine.

I do see a hose close to the radiator cap on the engine block in the other photo. Is that it? If so that seems to be a dedicated place to connect an overflow tank. My engine doesn't have a dedicated connection so I need to tap into the cooling system somewhere.

Jahwork · 28-04-2019, 20:37

Hola Senor Skipmac,

I don’t believe you will be successful in using one of the water heater lines. Where was the original overflow/expansion tank plumbed? The “radiator” cap, or in this case heat exchanger cap, is essentially a spring controlled valve, not unlike a relief valve on a hot water tank. It allows excess pressure, that above the rated spring pressure of the cap, to be eliminated through the hose to the expansion tank. Then as the engine cools and creates a vacuum, the coolant in the expansion tank is drawn back into the system to prevent air pockets, collapsed hoses, loss of coolant, etc. As you can see the expansion tank connection hose must be in the correct location for the system to work correctly. At least that is how I understand it to work. I have been wrong before many times, just ask my wife, and it wouldn’t surprise me if someone was to tell me I am wrong once again.

I hope you get it figured out.

Safe Journeys!!

~Jake

Uncle Bob · 28-04-2019, 21:15

Quote:

Originally Posted by Jahwork

Hola Senor Skipmac,

I don’t believe you will be successful in using one of the water heater lines. Where was the original overflow/expansion tank plumbed? The “radiator” cap, or in this case heat exchanger cap, is essentially a spring controlled valve, not unlike a relief valve on a hot water tank. It allows excess pressure, that above the rated spring pressure of the cap, to be eliminated through the hose to the expansion tank. Then as the engine cools and creates a vacuum, the coolant in the expansion tank is drawn back into the system to prevent air pockets, collapsed hoses, loss of coolant, etc. As you can see the expansion tank connection hose must be in the correct location for the system to work correctly. At least that is how I understand it to work. I have been wrong before many times, just ask my wife, and it wouldn’t surprise me if someone was to tell me I am wrong once again.

I hope you get it figured out.

Safe Journeys!!

~Jake

Jake, you are correct. The overflow tank has to be connected after the pressure cap. Non recovery systems have a pressure cap with one seal at the base of the spring seat, recovery systems have a cap with two seals, a second directly under the cap as well as the other.

captstu · 29-04-2019, 04:52

I removed the pressure regulator in the cap. This allowed me to connect the overflow line directly yo the tube under the cap, keeping the heater lines untouched. Works fine.

sailcrazy · 29-04-2019, 09:29

What about the location/elevation of the overflow tank? Does it need to be level with the the cap, or higher? or lower? Or does it not make any difference?

artisanmach · 29-04-2019, 09:48

The coolant recovery system works in conjunction with the radiator cap. using the fitting attached to the radiator cap. it allows for expansion of the coolant. if you look at your radiator cap it has two seals/gaskets the one under the spring allows bi-directional flow
without leaking around the outer seal.

**skipmac** · 29-04-2019, 09:51

Hi Jake

Quote:

Originally Posted by Jahwork

Hola Senor Skipmac,

I don’t believe you will be successful in using one of the water heater lines.

Why not? They are part of the pressurized fresh water cooling system.

Where was the original overflow/expansion tank plumbed?

If I could remember or had the foresight to document the original installation I wouldn't be asking on the forum.

The “radiator” cap, or in this case heat exchanger cap, is essentially a spring controlled valve, not unlike a relief valve on a hot water tank. It allows excess pressure, that above the rated spring pressure of the cap, to be eliminated through the hose to the expansion tank. Then as the engine cools and creates a vacuum, the coolant in the expansion tank is drawn back into the system to prevent air pockets, collapsed hoses, loss of coolant, etc. As you can see the expansion tank connection hose must be in the correct location for the system to work correctly. At least that is how I understand it to work.

All this I understand in theory.

I have been wrong before many times, just ask my wife, and it wouldn’t surprise me if someone was to tell me I am wrong once again.

I hope you get it figured out.

Thanks. Me too.

Safe Journeys!!

~Jake

**skipmac** · 29-04-2019, 10:07

On my engine this cannot work with the radiator cap. The cap has no provision for attaching a hose over or under the pressure seal. The cap is pressure rated but sits right on top of the tank and there is no way to tap into that setup without major modification IE welding and machining. Since the tank was attached before and I have NOT modified anything other than removing some hoses then it was connected somewhere else.

Additional information.

The hose to the existing overflow tank is not a small tube like between the radiator cap and the overflow tank on my car. instead it is +/- 3/4" ID which matches the hose connections on the back end of the header tank on the engine that previously went to the hot water heater.

Also, I have to get back to the boat to confirm but if I recall correctly, the overflow tank also has a pressure rated, radiator type cap so can be part of the pressurized cooling system.

artisanmach · 29-04-2019, 10:44

if you have an expansion tank with its own pressure cap you can put it in line with radiator hose...or anywhere just make sure the cap on the radiator is rated a couple of psi higher than the cap on the expansion tank. the only other consideration is you want to attach the hose to the highest point on the system so you are not trapping air in the system.

**skipmac** · 29-04-2019, 12:27

Quote:

Originally Posted by artisanmach

if you have an expansion tank with its own pressure cap you can put it in line with radiator hose...or anywhere just make sure the cap on the radiator is rated a couple of psi higher than the cap on the expansion tank. the only other consideration is you want to attach the hose to the highest point on the system so you are not trapping air in the system.

Thank you. This is the information I've been trying to get.

Only problem, again without major modification, there's no place to attach a hose to the highest point in the system. My idea is to completely fill the header tank through the existing radiator cap, close that, then add coolant to the expansion tank hopefully not trapping (much) air in the system.