Over heating on a Yanmar 18hp

[steveebryant]

Anyone know anything at all about small diesel engines?
I had to replace a hose that ran from the engine to the domestic water heater on the boat. Of course a lot of coolant ran out. When I reconnected the hoses and filled that part of the water system, the engine started to overheat.
On this 18 hp Yanmar, there are two separate water systems. One for heating domestic water; this is a closed system which employs a heat exchanger of sorts and is the system that I was working on. The other water system is use for cooling the engine; this system takes water from the lake to cool the engine. To my knowledge, the two systems are not connected.
The engine has been run a total of 20 hours since I have owned it and it has never over heated. After I changed the domestic hot water hoses, the engine will get hot after running but a few minutes.
Anyone got a clue what might be going on?
Thanks,
Steve

 

[John T1594]

Air bubble

A very common problem with these engines is that an air bubble or air lock forms in the system when you change coolant. It usually occurs around the water pump or any high place in the system. You have to find a way to burp that air either by removing a hose or with an air bleed screw on the pump - if you have one.
Sometimes the air will clear after the engine cools down and you can add more coolant through the fill port on the heat exchanger. I'm sure others will have some more specific advice.

 

[Dean Strong]

This sounds like a Yanmar 2gm20f. Most of the time when they overheat it is because the sea water intake is blocked, usually at the filter. So besides making sure the closed system is full (it should have a tank, similar to a radiator overflow tank in a car), check that you don't have a coincidental block in the seawater system that has nothing to do with your change of hoses. Wouldn't be the first time for me.

If you've only put 20 hours on the engine, you haven't owned it long. Check the seawater intake filter EVERY time you start the engine. Make it a habit. Hang the engine key on the seacock, which should be closed after every use, and is near the sea water filter. Before opening the cock, check and clean the filter. You'll never have an overheating engine if you make this your routine.

 

[steveebryant]

Thanks Dean, I thought I had a good place to keep the key but now I know better and thanks,
Steve
PS--I believe that my problem was that I did have a bubble of air in the closed cooling system and after I tightened the engine belt, that water pump was sufficiently strong enough to force the air out.

Is your boat equiped with the Yanmar 2GM20F?

Cheers,
Steve

This sounds like a Yanmar 2gm20f. Most of the time when they overheat it is because the sea water intake is blocked, usually at the filter. So besides making sure the closed system is full (it should have a tank, similar to a radiator overflow tank in a car), check that you don't have a coincidental block in the seawater system that has nothing to do with your change of hoses. Wouldn't be the first time for me.

If you've only put 20 hours on the engine, you haven't owned it long. Check the seawater intake filter EVERY time you start the engine. Make it a habit. Hang the engine key on the seacock, which should be closed after every use, and is near the sea water filter. Before opening the cock, check and clean the filter. You'll never have an overheating engine if you make this your routine.