antifreeze overflow

[Frenchy]

Hi- I've got a question that I can't find the answer to online and I'm hoping someone can help.
On my new engine, I have a water heater in the port cockpit locker and a brass coolant tank above it with a plastic overflow capture tank. The upper cap is rated at a lower pressure than the cap on the engine, as it should be.
Theoretically, I'm guessing, the overflow tube on the lower engine cap shouldn't ever receive any coolant, because the
upper cap would release first.
However, I'm losing coolant from the plastic capture tank. There's coolant in the bilge and the overflow
tube on the engine is wet inside.
Should that lower overflow tube be capped? Or- should the engine coolant cap should be upgraded to a higher
pressure?
Maybe there's an air block in the system and that's not letting the upper cap release? Thanks for any help -
Jean

[Paul D.]

I would call the engine manufacturer for sure but it may just need to work through and get to the level that works for that motor and installation. Agreed that this shouldn't leak like that. If you know who did the installation that may be a place to call too and at least let them know, especially if something more extensive needs to be done according to the engine manufacturer. If it is a new BetaMarine motor, I bet they will be helpful.

[wikakaru]

Sorry, I'm not understanding. Is your water heater the kind with an engine coolant circuit, or is it just that the overflow tank is located above the (otherwise unrelated) water heater?

On a boat I had with a water heater engine coolant circuit there was only one coolant overflow tank and pressure relief cap in the whole system, and that was on the engine. However, my water heater was at a level below the engine's cooling system.

Maybe a sketch of your cooling system would help.

[Frenchy]

Yeah, the water heater is in the engine coolant circuit and is located above the engine, which necessitates a small
coolant tank located above everything. That small coolant tank has a recovery bottle (plastic) plumbed to the radiator
cap. The radiator cap on that small tank has to have a lower pressure rating than the one on the engine so that only
it will release coolant to the recovery bottle when the heat and pressure rises. When the engine cools, the pressure
drops and the radiator cap sucks up the coolant in the recovery bottle until the pressure drops to a point where the
valve in the cap closes. Thats the way it's supposed to work (I think)
I've lost maybe a pint of coolant in the bilge over about 15 hours run time. Perhaps there's air in the system,
which is difficult to remove. The issue may resolve itself over time as air is purged. I'll add coolant and wait and see.
- Jean

[wikakaru]

Check out this article: https://stevedmarineconsulting.com/water-heater-primer/

From the article: If the heat exchanger within the water heater or any portion of the plumbing between the engine and the water heater is located above the engine's expansion tank cap, then a remote expansion tank must be plumbed into the system. This tank, with its own pressure cap, then becomes the primary fill point for the closed cooling system, rendering the original legacy fill cap dormant and unusable.

I would think that the hose to the engine's original overflow tank should be capped and the tank should be removed, too.

Also, see here: https://www.betamarinenc.com/installation-basics/

Good luck.

Jim

[Frenchy]

All right, thanks Jim. I can, apparently plug the drain hose to the original "radiator" cap. I can't remove the tank-
it's an integral part of the engine. - Jean

[Jim Walsh]

I have an expansion tank located above my water heater (which is above my engine) in addition to the normal recovery tank mounted above the engine. My mechanic told me both were required for my installation. I never touch the primary cap on the engine.