Advice freshwater system

[carlager]

I have drained the coolant in the fresh water system our Yanmar 3gm30f. The system has a subtank and coolant also runs through a hot water heater.

Recently I supplied new coolant by filling up to to the minimum level of the subtank and to the mouth of filler port on the heat exchanger, where the hose runs to the subtank.

After the supply of new coolant I ran the engine in idle for about 30 minutes.

When opening the fillercap on the heat exchanger I noticed that the coolant level had decreased whereas the level in the subtank had increased to between minimum and maximum.

I recall that the level in the subtank was at the minimum mark and the level in the heat exchanger up to the mouth of the filler cap before I drained and supplied the system with new coolant.

So I am wondering if something is wrong now

[Harter]

Ok after replacing coolant and running the motor the coolant will expand as it heats up to operating temperature, now as it heats up it will push out to the sub tank, trapped air in the cooling system will move to the heat exchanger,
Now the rad cap.. This is a item that is very over looked, depend on age of the cap, It has to maintain 12 to 15 psi pressure in the cooling system,
It opens as the motor cools down and allows coolant to return to the heat exchanger. I am thinking you have check the levels when the motor was still hot,, ok So top up the the exchanger and run up to operating temp again, after allow motor to cool off again recheck fluids,, All should be good. please do a search on the net about rad caps,, lots of info.

[carlager]

Thank you for your reply. It makes good sense.

Is it correct that the rad cap is not functioning if coolant does not flow back to the heat exchanger when the engine is cold ?

[Harter]

That is very possible,, As the coolant cools down it creates a vacuum in the exchange,, That pulls the coolant from the over flow tank, The cap has two seal area and a spring on it, top seal on the cap keeps fluid in the rad, bottom seal allows extra fluid to move to the over flow and return as the motor cools down
Now in your case you would have air in the coolant system after draining, That would be why the exchange level was not full when you check it, But having air in there may cause the fluid to not flow aback from the over flow.
I would top up the exchange and warm up the motor again, Then after the motor has cooled off recheck fluids,

[carlager]

Thank you again. I will do as you recommend

[Harter]

It should be ok,, But depends of the age, Like all things.. LOL
I started jogging after work,, holy crapp that hurts,, LOL I am 55 years old

[carlager]

Maybe you are jogging too hard

[goboatingnow]

Originally Posted by Harter

It should be ok,, But depends of the age, Like all things.. LOL
I started jogging after work,, holy crapp that hurts,, LOL I am 55 years old

I'd reccomend a slow walk to the pub. At your age who are u trying to impress.

Dave

[Harter]

I would love a walk to the pub,, Problem is I am in Iraq working, No pub,,

[carlager]

Problem solved.

Coolant was sucked from the subtank to the heat exchanger when the engine was allowed to cool off for a whole night.


Thanx a lot for your help

[Harter]

Always happy to help,, I am mostly lurking here, Well until I buy my boat, I am very close to being able to to that, But a lot to learn first,, How do you get them to surf???
Just kidding LOL