I have a Yanmar 4JH3E about 6 years old with about 400 hours on it. Couple of weeks ago I was running up a river at very low RPM, almost idle and noticed the temp gauge was about 210, it normally runs at 180 or so. I lowered rpm, no change, put the boat in neutral and increased rpm above 2k, the needle 'popped' down to about 180 where it stayed the rest of the day. I guessed the thermostat had been stuck and the vibration shook it loose so I installed a new thermostat today. Basically, the same thing happened as before, at idle in the slip the engine continued getting warmer, up about 200 after 5 minutes or so, I revved it up to 2k and it needle dropped FAST all the way to 120 or so. Plenty of raw water being discharged Plenty of fresh water in the system. Could this be the sending unit or gauge (I'm hoping for another other what water pump!) Any ideas appreciated!
Engine problem (gauge shows overheating)
- Thread starter Persy
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Check the Impeller
Did you check the impeller,at low rpm's it might not be pumping the same. When did you check it last.
Did you check the impeller,at low rpm's it might not be pumping the same. When did you check it last.
heat exchanger
Try checking the heat exchanger; more water flow thru there (increased rpm's) means greater cooling. 4 to 1 muriatic acid works great on the calcium deposits in the heat exchanger. Remove the heat exchange first.
Try checking the heat exchanger; more water flow thru there (increased rpm's) means greater cooling. 4 to 1 muriatic acid works great on the calcium deposits in the heat exchanger. Remove the heat exchange first.
we have a winner...I think..
checked impeller, which I didn't before as I had seen water coming out of exhaust, and sure enough...missing 3 blades. Put in new impeller and all is well...so far... Where did the broken blades go? just through the system exhaust into the sea? I had BIG problems with my generator as when impeller went bad, blades broke and clogged up exchanger....hope that these just pass through...anyone ever have to go through the engine and clean them out?
checked impeller, which I didn't before as I had seen water coming out of exhaust, and sure enough...missing 3 blades. Put in new impeller and all is well...so far... Where did the broken blades go? just through the system exhaust into the sea? I had BIG problems with my generator as when impeller went bad, blades broke and clogged up exchanger....hope that these just pass through...anyone ever have to go through the engine and clean them out?
Guy
Inspecting the heat exchanger is one of those jobs which sounds a lot more complicated than it is. In your case, with three missing blades, it might be time to find out where they went before you have another problem sometime when you REALLY need the engine. I have the same engine and just this afternoon pulled the back off the heat exchanger just to take a look at how much stuff had built up. Took about a half hour tops unless you need to remove the whole thing which may double that time.
Inspecting the heat exchanger is one of those jobs which sounds a lot more complicated than it is. In your case, with three missing blades, it might be time to find out where they went before you have another problem sometime when you REALLY need the engine. I have the same engine and just this afternoon pulled the back off the heat exchanger just to take a look at how much stuff had built up. Took about a half hour tops unless you need to remove the whole thing which may double that time.
you're right...
I inspected the mixing elbow last month, but haven't gone into the exchanger and will do so....need to change out anti-freeze anyway...
I inspected the mixing elbow last month, but haven't gone into the exchanger and will do so....need to change out anti-freeze anyway...
Those blades are somwhere in the system
You will have to work from your impeller forward searching for blades. They will be there somewhere. Most heat exchangers are designed to trap broken blades so they will not enter the "exchanger" section. It will not be neccesary to drain your anti freeze to check the heat exchanger. You will be checking the "outside" section of your exchanger. That section only gets raw water from the sea and does not mix with your coolant.
You will have to work from your impeller forward searching for blades. They will be there somewhere. Most heat exchangers are designed to trap broken blades so they will not enter the "exchanger" section. It will not be neccesary to drain your anti freeze to check the heat exchanger. You will be checking the "outside" section of your exchanger. That section only gets raw water from the sea and does not mix with your coolant.
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