While returning to San Francisco Bay from the Sacramento River Delta, we started taking on water. The problem was that the hose from the heat exchanger to the vented loop came off on our Yanmar 2gm20F engine. After cutting a fresh edge on the hose and re-clamping it, things were great until a few miles later when we got an overheat alarm. The alarm went away 30 seconds after throttling back. We did observe that there was not much water coming out the exhaust. After checking the strainer, we motor sailed back at about 2500 rpm with no more alarms. Last weekend, I checked the entire system (which looked clear), and tested the raw water delivery by taking the same hose off and starting the engine for about 5-7 seconds with a plastic container over the hose nipple. The system delivered about 32 ounces of water in this time--a very healthy amount. However, there is not nearly this much water coming out of the exhaust, and there are little white puffs of smoke. I am starting to suspect a clogged vented loop or the mixing elbow. I am thinking that perhaps back pressure from a clog may have contributed to the hose blowing off in the first place. I believe both the vented loop and the elbow are original equipment on the 1991 engine. Has anyone else encountered this situation? I am going to try to finish troubleshooting it this weekend. Gary s/v "Serenisea"
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Oh yes, check the elbow
I believe other than the impeller, the elbow is the most likely cause of a overheated engine. I just replace my elbow about 2 months ago. It was clogged pretty bad. Before replacing it, I did all the similar tests as you. I checked the water going through the heat exchanger, impeller, etc, but it came down to be the elbow. Once you take it off, you may be able to clean it out by carefully chipping off the carbon buildup. That may last you for a while, but a better option is just to replace it, especially if it has been there since 1991. It will cost you about $200.
I believe other than the impeller, the elbow is the most likely cause of a overheated engine. I just replace my elbow about 2 months ago. It was clogged pretty bad. Before replacing it, I did all the similar tests as you. I checked the water going through the heat exchanger, impeller, etc, but it came down to be the elbow. Once you take it off, you may be able to clean it out by carefully chipping off the carbon buildup. That may last you for a while, but a better option is just to replace it, especially if it has been there since 1991. It will cost you about $200.
And,,
You probably don't need that vented loop. Check a Yanmar shop manual and you'll see that they are for installations below the water line. It's almost impos,,,,no, it's impossible for a modern 'euro' designed boat like a Hunter to siphon water back through the exhaust. I tossed mine. Now I don't have messy salt water dripping in my engine room. Oh, clean/replace that elbow.
You probably don't need that vented loop. Check a Yanmar shop manual and you'll see that they are for installations below the water line. It's almost impos,,,,no, it's impossible for a modern 'euro' designed boat like a Hunter to siphon water back through the exhaust. I tossed mine. Now I don't have messy salt water dripping in my engine room. Oh, clean/replace that elbow.
Elbow
Gary, That is exactly what my 37.5 did several years ago. Replaced the elbow and no problems since. Les
Gary, That is exactly what my 37.5 did several years ago. Replaced the elbow and no problems since. Les
Fred
Its a good point you make. On my 376 the valve on the vented loop drips and has caused the paint on the rocker box to bubble - ie. rusting underneath. I guess you reason the mixing elbow is high enough to act as a syphon break. How did you determine its level above WL? I also put 4" of 1" OD clear acrylic tube in line with the raw water feed to the mixing elbow so now I can see the cooling water moving. Needs cleaning about once a year but it certainly beats tying a shaving mirror to a stick and dangling it over the stern. Yes I have done that!
Its a good point you make. On my 376 the valve on the vented loop drips and has caused the paint on the rocker box to bubble - ie. rusting underneath. I guess you reason the mixing elbow is high enough to act as a syphon break. How did you determine its level above WL? I also put 4" of 1" OD clear acrylic tube in line with the raw water feed to the mixing elbow so now I can see the cooling water moving. Needs cleaning about once a year but it certainly beats tying a shaving mirror to a stick and dangling it over the stern. Yes I have done that!
One way to find the water line from the inside
Disconnect the raw water seacock, connect a long clear hose to it, and raise the other end of the hose, and then open up the seacock. The water will level off, and that is the water line. If you don't have a clear hose, use a section of a garden hose. Connect the hose, raise the other end, open the seacock, then slowly lower the other end until water starts to flow out. That is the water line.
Disconnect the raw water seacock, connect a long clear hose to it, and raise the other end of the hose, and then open up the seacock. The water will level off, and that is the water line. If you don't have a clear hose, use a section of a garden hose. Connect the hose, raise the other end, open the seacock, then slowly lower the other end until water starts to flow out. That is the water line.
Good one JC!
Donalex, I just eyeballed it. Yanmars recommendations are 'to the extreme'. Modern Hunters don't even come close. And I like your idea of the clear hose too. It's going on the 'list'.
Donalex, I just eyeballed it. Yanmars recommendations are 'to the extreme'. Modern Hunters don't even come close. And I like your idea of the clear hose too. It's going on the 'list'.
Donalex: How can you see the water ?
through the clear acrylic tube? I would think you won't be able to see if the water is moving or not unless there are air bubbles or gunk in the water. Won't it just look like solid water in there? Did you install it just before the mixing elbow? To bad there isn't something like a free flowing paddle wheel in a clear box. If the wheel is spinning, that means the water is moving. By the way, where did you get the clear acrylic tube? Is it a hard tube or did you use clear + flexible water hose that you can buy at West Marine? I think this is also going to be one of my project during this winter.
through the clear acrylic tube? I would think you won't be able to see if the water is moving or not unless there are air bubbles or gunk in the water. Won't it just look like solid water in there? Did you install it just before the mixing elbow? To bad there isn't something like a free flowing paddle wheel in a clear box. If the wheel is spinning, that means the water is moving. By the way, where did you get the clear acrylic tube? Is it a hard tube or did you use clear + flexible water hose that you can buy at West Marine? I think this is also going to be one of my project during this winter.
Check the nipple
I had the same thing happen on my H34. Turned out to be the brass nibble that connects the raw water exhaust to the mixing elbow. Seems to be a spot that collects soot, and when mixed with water, it becomes a solid, concrete-like blockage. In talking to a mechanic, that was a common problem. Pulling the nibble off was a lot easier then pulling mixing elbow!
I had the same thing happen on my H34. Turned out to be the brass nibble that connects the raw water exhaust to the mixing elbow. Seems to be a spot that collects soot, and when mixed with water, it becomes a solid, concrete-like blockage. In talking to a mechanic, that was a common problem. Pulling the nibble off was a lot easier then pulling mixing elbow!
Let me elbow my way in here
2GM20F is notorious for requiring a new mixing elbow every 5 years. It's impossible to remove at the elbow fitting, so remove the four bolts at the manifold and take the two parts home to blast the elbow off the manifold. Note that there are 2 short and 2 long bolts here. Don't try to clean the elbow, waste of time. Get a new one for $150 and rest easy for 5 years. Be sure to get the gasket for connecting the elbow to the manifold. By all evidence, this is your problem, and it's fairly easy to solve. Take heart.
2GM20F is notorious for requiring a new mixing elbow every 5 years. It's impossible to remove at the elbow fitting, so remove the four bolts at the manifold and take the two parts home to blast the elbow off the manifold. Note that there are 2 short and 2 long bolts here. Don't try to clean the elbow, waste of time. Get a new one for $150 and rest easy for 5 years. Be sure to get the gasket for connecting the elbow to the manifold. By all evidence, this is your problem, and it's fairly easy to solve. Take heart.
JC - Water
I cut the rubber raw water tube between anti-syphon bend and the injection bend and inserted a short length of 1" OD clear acrylic tube. When the engine is stationary the tube looks - well - empty. At idle one sees bubbles and turbulence, though I don't know where the air comes from - maybe sucked in via the anti-syphon valve. At higher speeds the tube is completely full and looks very different. Try it with a glass of water. To make it more obvious I stuck a strip of tape along the back of the tube like a clinical thermometer. It works, you have my word.
I cut the rubber raw water tube between anti-syphon bend and the injection bend and inserted a short length of 1" OD clear acrylic tube. When the engine is stationary the tube looks - well - empty. At idle one sees bubbles and turbulence, though I don't know where the air comes from - maybe sucked in via the anti-syphon valve. At higher speeds the tube is completely full and looks very different. Try it with a glass of water. To make it more obvious I stuck a strip of tape along the back of the tube like a clinical thermometer. It works, you have my word.
Donalex: Thanks.
It is going to be one of my winter projects. I will probably use a section of clear flexible tubing you can buy for water. I wouldn't think water will get too hot for it. Thanks a bunch.
It is going to be one of my winter projects. I will probably use a section of clear flexible tubing you can buy for water. I wouldn't think water will get too hot for it. Thanks a bunch.
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