Engine Question #1: Coolant Overflow Tank

[Joe Mullee]

I have a Yanmar 3GMF which is cooled by fresh water passing thru a heat exchanger that is filled with coolant. There is an overflow tank for the coolant. There is very little coolant ever in that tank, either when the engine is running or when it's off and cooled down. When I take off the cap and inspect the coolant level in the heat exchanger it's filled right to the top. Shouldn't there be more coolant in the overflow tank. The level seems to stay constant and is always below the "low level" line. Shoud I just add coolant to the tank itself? There's no more room in the heat exchanger. As I said it's filled up. Thanks. Joe Mullee

 

[Bonnie]

Coolant overflow tank

If you notice your tank is mounted above the engine so the fluid will flow by gravity into the engine. Whenever you remove the radiator cap you are allowing the fluid to escape the system. With these tanks you don't need to check the level in the radiator just keep an eye on the level in the tank. You need to keep the tank filled to anywhere between the full and add marks with a coolant mixture. I use the newer red type mixed 50/50 with distilled water.

 

[Joe Mullee]

So should I fill ......

the overflow tank up between the marks? There is a very little amount of coolant in the tank but it never seems to go up or down and it's a little below the "low" mark.

 

[Ron Mills]

Top of aux. tank should be

the exact same height as the radiator cap for proper operation of the aux. tank.

 

[Bill]

The sub tank is not for filling

Joe, one of the things I learned at the Engine City Technical Institute (Mack Boring) Yanmar maintenance class is that the sub tank is not your indicator whether the coolant is at the right level--topping it up between the lines is not how this is done. You should ignore the level indicator in the sub tank, and just inspect the level under the filler cap (though not when it's hot!) Also, Ron is right: the sub tank should be mounted so that its top is level with the feed from under the filler cap. You can confirm this in Chapter 15 of the Yanmar Service Manual, which also explains the function of the sub tank.

 

[Don Alexander]

Expansion Tank

to give it its proper name. When engine is hot fluid expands and escapes into the plastic tank and when the engine cools down it draws fluid back. The cap on your heat exchanger MUST be an airtight fit and it doesn't matter how high or low the tank is - within reason.Autos have same system. Suggest you keep it about 50% with coolant.