High Pressure in the Coolant Expansion Tank

Try posting that question on boatdiesel.com. Forums specific to your engine. Very helpful

Hi,

What temp is the coolant getting to when you have this problem and do you re fill the expansion tank everytime you use the boat?

Let's start the troubleshooting in an orderly manner.

For a start ...

What make and model of engine? (Is it a MaN that requires jacket water pressurization?)

Where are you measuring coolant pressure?

Is the coolant expansion tank overflowing so the loss occurs at that point or is it vanishing someplace else?

Have you tested the coolant for combustion gases?

Have you used a tracer dye test to look for coolant leaks?

Hi,

If you don't top up the expansion tank how much comes out next time you run it?

Is there a recovery bottle? Is the cap of correct type?
Lots of minds here to help, we need some more info.

Please see my replies inserted into the quote

Tracer dyes glow brightly under UV light. That makes it very easy to find leaks from systems which have it added. Your existing coolant may or may not already flouresce but a tracer dye removes all doubt as to the source.

But, if as you say the loss is through the cap, make sure the right cap is installed and is working properly. If the expansion tank is pressed up when cool and the cap is installed then normal expansion will blow a lot out and create considerable pressure.

Do you have a recovery tank installed? Is the expansion tank cap the right kind for use with a recovery tank?

When you refill the tank do you fill it completely to the edge of the cap?

What is the pressure rating marked on the cap itself?

K1W1 asked: "If you don't top up the expansion tank how much comes out next time you run it?"

That is a very important question because if you don't lose any more and the pressure does not exceed the cap rating then you may be overfilling it.

What happens after the 4 liters gets blown out? Does more coolant keep flowing? Do you get "steam" or vapor? Does the pressure drop? Does the engine temperature increase?

Couple Suggestions from an amateur!

I don't know what you have for engine coolant but I am assuming it is not raw water... ! OK enough joking.

Check the exhaust for a different smell usually leaks that are serious show up that way... now don't know what coolant you are using so that may not work. Its a real rough guide but if you smell coolant in the exhaust you are in deep merde!

Back to minor leak checking suggestions.
While engine is cold fit a pressure adapter to the coolant expansion tank or the cap... use a regulated source of compressed air to pressurize to the correct running pressure. What to use well you can adapt a engine leak down tester and use it but if you know how to use that don't accept any leak down rate! But IMPORTANTLY... If the coolant goes down in the tank... you gotta leak. Now it will go down at first a little because of hose expansion and the like but it will stop quickly. If it keeps going down that is the key.

First place I would check is the heat exchanger to raw water... or any other heat exchanger. You might need to remove the cover to get access to the inside. Now if you have a sonic leak tester you can use that to find the leak... this works better if the coolant has been drained but will work without draining. This is a microphone that picks up the sound of leaks... one like they use to check vacuum bag leaks in composite manufacture... you wonder how the boat builders find the leaks in the vacuum bags... that is how. The sound is different with water than an air filled system. I learned when I involved with race cars... the coolant systems would be pressure checked before filling with coolant and the ultrasonic leak test done with air... .

If you cannot find the leak then you warm the thing up to operating temp. and then shut down and do the pressure leak testing. But try cold first as it is easier to check around a cool engine than a hot engine.

I have one question, Why is dbltime trying to refer OP to another website ?

Probably because he/she can

Thanks for the reminder. The tragedy of man is he forgets.

A few questions are in order...

What make / brand of engine, year, model, how many engine hours, and what is the engine condition details would help the experts here?

Predominately do you do your own service... have a hired engineer or captain doing it... or do you use the manufacturers service ?

What is the coolant temperature verses power, and where is this measured?

What specification does the manufacturer have for coolant temperature ?

Now to be clear... the pressure is what at normal cruise?

At high power... the pressure goes up to 1.8 bar and then stays there!

What happens to coolant level at startup to warmed up and operating at normal cruise?

What happens to coolant level from warmed up operating at normal cruise to the high power output conditions?

Can you estimate if and how much coolant loss there is... may be none! This last question seems not to apply but just checking.

One last attempt ...

What happens after the initial 4 or 5 liters are expelled through the cap?

Is the loss ever more than that amount?

Do you fill the expansion tank to the brim before closing the cap?

There is a reason that tank is called an "expansion tank."

You are not helping much by not providing answers to the questions that probably hold the answer.

As an aside, if you are filling the tank to the brim then putting the cap on, you have to expect the coolant to be lost as it expands. If you replace the venting cap with a closed cap and gauge, the expanding coolant can reach very high pressure very quickly. You are lucky it hasn't caused damage to the system elsewhere.

In normal operation, the coolant pressure should not exceed the pressure rating marked on the cap - you never answered that question either - and if the expansion tank is overfilled it will expel enough water to relieve the pressure above the marked maximum pressure then go no higher unless there are combustion leaks or a high temperature condition.

If coolant is normal or low (which implies an air space in the X tank) and you have 1.8 bar pressure the coolant temperature has to be around 130*C so if it stays at 85 you need to reconsider the story, your test methods, or your temperature monitoring equipment.