Overheating 3GMF

[Claude L. Auger]

As I pulled out of my slip yesterday, I notice some white smoke coming out of my exhaust. I did have plenty of water coming out of the exhaust. Running the engine to 3000 (max RPM for my 20 HP is 3400)quickly brought an overheating situation and there was plenty of steam in the engine room as well as a hissing sound as if water was thrown on hot metal. I shut the engine down and we sailed all day. Before coming back in, I refilled the system with the proper mixture of antifreeze and water, as well as the overfill tank, which had also been drained, and started the engine only when I was about to pull into the slip.I went back today to investigate.1) Lake water is already too cold to jump in (we haul out on 10/15 for the winter) but I had lots of water coming in through the through-hull.2) Impeller checked out OK. No signs of wear and no visible-cracks.3) Thermostat opens and shuts properly when checked in boiling water. It is marked for 71 degrees, and it did open before water boiled (100 degrees C).4) All antifreeze had found it's way in the bilge, yet none of the hoses were leaking.5) Even with the engine not running, whatever coolant I add through the rad cap vanishes rapidly. I did not let the engine run long enough today to avoid overheating it.Has anybody ever had this problem, and if so, what might be the solution. Thanks in advance.

 

[Noel Black]

Hot Water tank hoses could be leaking

The engine will have two hot water hoses running under the floor pan to the hot water tank. I had one leak. Have not pulled the hose yet, just capped the hoses where they left the engine.Noel

 

[Stephen Ostrander]

possible air block?

Check the bilge for signs of anti-freeze from a leaking heat exchanger hose. BTW, You haven't by any chance recently drained and changed the engine coolant? Sometimes you can get an air buuble in the system.

 

[Claude L. Auger]

Overheating 3 GMF Tks

Thanks Noel & Stephen. No air lock, but checking the hoses led me to water heater. Hoses OK, Heat exchanger in Water Tank busted, and leaking through the bottom. I had noticed a little wetness and some rust, and I figured I would need to change the heater next spring. I yanked the hoses away and join them together with a piece of copper pipe and stainless steel clamps. Voila ! No more leaks and after running engine for 1½ hour at +/- 1500 RPM with some short peaks at 3000, engine heat exchanger is still coll enough for me to put my hand on it. I did not have time to take boat out and try it under load, but will do so this week-end. I still have a little bit of white smoke however and wonder about that. Exhaust water is cold to the hand so it cannot be steam. Besides, it smells a little bit like by-product of combustion. Engine seems to run find.If I have overlooked anything, please someone let me know. BTW, the water heater is currently sitting on the curb waiting for pick-up by garbage collectors. When I took it out, the botton completely disintagrated I'll get around to buying another one in the next few weeks.

 

[Robert Dean]

HOT WATER TANK LEAK

Claude,I had the same type of hot water tank leak last year on a H35 circa 1989. My tank was probably put in, in the 1988 time frame.I suspect that the reason for my leak was too much (ie too strong) of an anti freeze solution.Yanmar has gone to the red based anti freeze as opposed to the green auto based some people use.The Yanmar engine book calls for this fresh water heater loop to use a "clear" liquid.What is clear ?? I would tend to think that some people use tooooo much of an anti freeze solution and the metal in the hot water tank is not that strong and carrodes easily.Sail on Bob Dean

 

[Jim Oursler]

Missing coolant on 3GMF.. don't drink the water

Having had a few boats.. if it is leaking out.. either a leak in the engine, or a leak in the water heater.. I would bet on the heater. Bet that your hot water tastes like antifreeze..