Hello all. I have a Yanmar 2GM20F. After running for about 30 to 40 minutes at 2800 RPMs, my temp alarm sounds. I put the transmission in neutral, increase RPMs to about 3200 and after a short time the alarm goes off. Then I continue on (in gear) at about 23-2500 RPMs and all is well. The manual says I should be able to operate at 3400 continuous. I seem to be getting good water flow, and the sea water strainer isn't clogged. The impellor was changed at the end of last season, and MOST of the hoses have been replaced within the past year. While looking for the problem, I checked the oil and was low about a half-quart. I wouldn't think that would be a cause. I'm sure I have the correct blade
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K
KennyH
Had this problem
Had this problem on my Cheoy Lee with Westerbeak four cyl diesel. Was only corrected by back flushing the heat exchanger. I believe mine had some pieces of impeller that would not flush in the normal direction but when backflushed came loose and where history. Just used a water hose and disconnected the feed into the heat exchanger and out of the heat exchanger.
Had this problem on my Cheoy Lee with Westerbeak four cyl diesel. Was only corrected by back flushing the heat exchanger. I believe mine had some pieces of impeller that would not flush in the normal direction but when backflushed came loose and where history. Just used a water hose and disconnected the feed into the heat exchanger and out of the heat exchanger.
K
Karl
Return Line
Hey Harry, I had this same problem on my 30GM30F. I finally tracked it down the the connector where the seawater returns to the exhaust elbow. The connector is just a small "L" shaped fitting, and it got clogged with the particles from the diesel exhaust. I had to take the connector off and literally chip the build-up away. It was as solid as concrete. Might be your culprit as well.
Hey Harry, I had this same problem on my 30GM30F. I finally tracked it down the the connector where the seawater returns to the exhaust elbow. The connector is just a small "L" shaped fitting, and it got clogged with the particles from the diesel exhaust. I had to take the connector off and literally chip the build-up away. It was as solid as concrete. Might be your culprit as well.
S
Sam B
Overheating
I had the same problem on my Hunter 386 this month. I left my boat in the water during the winter and I did not clean the bottom before the summer season. Moss had built up on the intake under the waterline which caused a restricted water flow. I cleaned it underwater and now my engine is back to normal. I hope this is your problem. Good Luck...
I had the same problem on my Hunter 386 this month. I left my boat in the water during the winter and I did not clean the bottom before the summer season. Moss had built up on the intake under the waterline which caused a restricted water flow. I cleaned it underwater and now my engine is back to normal. I hope this is your problem. Good Luck...
How hot is the mixing elbow?
First, you should cruise a 2GM20F at 2850 or 2900 rpm; 85% of continuous max rating. If you are really overheating, the raw water system is restricted somewhere. To make sure you are really overheating, try touching the mixing elbow next time the alarm goes off. You should always be able to touch the mixing elbow. Here in the NW where water temp is about 58 degrees, mine always stays very cool, even after several hours. In NJ, ocean raw water may be warmer, but the elbow should not be real hot to the touch (meaning you can leave your finger on it for several seconds). If you have checked the strainer and it is clear, disconnect the raw water hose (with the cock closed) on the intake side of the impeller, and connect a garden hose to it (with a fitting and clamp, and the cock open). Back flush the system at the highest pressure. Because this is such a problem in the NW (pesky eel grass), I rigged a section of garden house so it fits from the galley faucet to the impeller intake hose. I can back flush at any time. If that doesn't do it, check out the impeller (it's easy). Something could have worked its way through and damage one of the blades. It's not a bad idea to replace it yearly. If the impeller is okay, your mixing elbow is clogged. Pulling and cleaning the elbow is easy or very difficult, depending on how corroded it is.
First, you should cruise a 2GM20F at 2850 or 2900 rpm; 85% of continuous max rating. If you are really overheating, the raw water system is restricted somewhere. To make sure you are really overheating, try touching the mixing elbow next time the alarm goes off. You should always be able to touch the mixing elbow. Here in the NW where water temp is about 58 degrees, mine always stays very cool, even after several hours. In NJ, ocean raw water may be warmer, but the elbow should not be real hot to the touch (meaning you can leave your finger on it for several seconds). If you have checked the strainer and it is clear, disconnect the raw water hose (with the cock closed) on the intake side of the impeller, and connect a garden hose to it (with a fitting and clamp, and the cock open). Back flush the system at the highest pressure. Because this is such a problem in the NW (pesky eel grass), I rigged a section of garden house so it fits from the galley faucet to the impeller intake hose. I can back flush at any time. If that doesn't do it, check out the impeller (it's easy). Something could have worked its way through and damage one of the blades. It's not a bad idea to replace it yearly. If the impeller is okay, your mixing elbow is clogged. Pulling and cleaning the elbow is easy or very difficult, depending on how corroded it is.
N
Nice N Easy
Another thought
All the previously mentioned ideas are good ones, but something not mentioned. Have you checked your thermostat. The Yanmar thermostats, at least on my 2QM, are very small, and it doesn't take much rust or debris to clog them or make them partially inoperable. I would certainly give it a look see.
All the previously mentioned ideas are good ones, but something not mentioned. Have you checked your thermostat. The Yanmar thermostats, at least on my 2QM, are very small, and it doesn't take much rust or debris to clog them or make them partially inoperable. I would certainly give it a look see.
Engine gauges
I am not a mechanic but this sounds like the problem I once had and it turned out to be a restricted mixing elbow. The problem you describe is a good reason to install a water temperature gauge to your 2GM20F and one for oil pressure at the same time. This is not particularly expensive or difficult and permits monitoring your engine whenever underway for great peace of mind and indication of problems before they become bad ones. Gauges can be installed and the buzzer/light remain operative.
I am not a mechanic but this sounds like the problem I once had and it turned out to be a restricted mixing elbow. The problem you describe is a good reason to install a water temperature gauge to your 2GM20F and one for oil pressure at the same time. This is not particularly expensive or difficult and permits monitoring your engine whenever underway for great peace of mind and indication of problems before they become bad ones. Gauges can be installed and the buzzer/light remain operative.
Several people here diagnosed raw water restriction, although you said you were getting "good" flow. Check your coolant hose at the heat exchanger discharge. If it is cool, then you have either a thermostat, temp sender, or instrument problem. You can check all three with a pot of hot water and a thermometer. You said the impeller was new last season. If it was idle for some time, check it again. The blades that were in the flexed position during lay-up can break when started up. I had one with less than 100 hours on it that broke after several months idle.
F
Farley
none
Have a Hunter 31. During a rebuild at my marina several years ago, i kept my boatin Rock Creek; not far from the Magothy. The following year, early into the season, my 2gm20 started overheating. Having checked everthing that has previosly been posted, it turned out that the heat exchanger was clogged with brine shrimp. Easy fix, remove the exchanger, bathe it HCL or muratic acid, available at any hardware store, and if you have checked everything else, I think this will solve your problem.
Have a Hunter 31. During a rebuild at my marina several years ago, i kept my boatin Rock Creek; not far from the Magothy. The following year, early into the season, my 2gm20 started overheating. Having checked everthing that has previosly been posted, it turned out that the heat exchanger was clogged with brine shrimp. Easy fix, remove the exchanger, bathe it HCL or muratic acid, available at any hardware store, and if you have checked everything else, I think this will solve your problem.
J
Jack
heat exchanger
I and several other boats have had troulbe with the Yanmar engine overheating - very similar to what you describe. Several of us have had the heat exchanger cleaned resulting in complete elimination of the problem.
I and several other boats have had troulbe with the Yanmar engine overheating - very similar to what you describe. Several of us have had the heat exchanger cleaned resulting in complete elimination of the problem.
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