Yanmar exhaust steam question

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Jun 18, 2004
3
Other Yamaha 29 center coc Wilmington, Calif
After over 2 years I finally got the engine rebuilt and left the dock under power. Completly rebuilt head, new pistons and rings, new bearings, fuel pump, impeller, alternator, fuel tank and the prop shaft is 2 yrs old. This is raw water cooled and the temp gauge shows about 160 at cruise speed. This is a yanmar 2gm20 engine. My question is, is 160 about the right temp for this engine? I could put my hand on the exhaust manifold but if felt a bit hotter than it should. Also not as much water comes out the exhaust as I think should be coming out but it seems that quite a bit of steam comes out the exhaust. Being as this is the first diesel I've had I'm not sure if thats normal or not. My mechanic says its just fine but I'd like others opinions as well. Thanks Tattoobob1@earthlink.net Y-29 InkMaster II Wilmington, Calif.
 

RichH

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Feb 14, 2005
4,773
Tayana 37 cutter; I20/M20 SCOWS Worton Creek, MD
Actually its a little on the hot side.

Your mechanic is correct ... and knowledgeable. For a raw water cooled engine the best solution is to have a 135 degree thermostat. The alternative thermostat is 180 degrees. What the cooler running 135 degree T'stat will do is tend to keep the cooling water well below the 'magic' temperature of ~153 degrees F., the temperature that dissolved carbonates will drop-out (precipitate) and rapidly form a fouling scale on the inside of the cooling circuit and inside the engine. That your engine is running close to the lower of the two available thermostats is a GOOD thing. Even with a 135 degree Thermostat there will be places in the cooling circuit that the water will be heated to beyond that magic ~153 degree F. mark and 'eventually' you will have to chemically 'descale/pickle' the engine to remove the formed internal scale. If your raw water cooled engine was running at 180 degrees or above -- that would indicate that you will sooner than later need to 'descale'/de-salt' the internals. Keep a mental track/log of the operating temperature and when your 160 degree gage temperature starts to climb noticably upwards (due to the internal fouling), then its time to consider to de-scale the engine so the heat transfer returns to be more efficient .... the formed/accumulated 'scale' retards the heat transfer and the higher temps. cause the scale to form 'faster'.
 
Feb 22, 2006
1
- - Sidney
Re: Steam in exhaust

Hi, I thought I would pass along a problem I encountered several years ago. I have a Yanmar 2gm raw water cooled engine. A water channel developed from the edge of the cylinder wall on the block to the outside edge allowing water from the jacket to enter the cylinder. This was happening from the time I bought the boat for about six months before total failure. It was a $1600 repair and the mechanic drilled a hole in the centre of the channel and put a flush stainless bolt where the gasket goes to make a seal. No problems since. I would suspect a lack of maintenance (not torqueing the heads for instance) was the cause. I am not suggesting this is your problem but worth passing on. Another issue I have had is spinning impellers on the water pump. The impeller worked fine at low rpm's but started to spin on itself as the rpm rose. I have had this problem with two Yanmar impellers and have switched to jabsco and the problem has been solved. I looked at the impeller and it appeared to be fine but when I put a screwdriver into the centre hole, the rubber impeller would spin on the shaft. It took me forever to figure out that one but no problems since I switched to Jabsco. I hope this helps. cheers john
 
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