I normally operate the 3GM30F on my H355 at 2700 rpm but several times I have need to run 3200 rpm. Both times that I have run at 3200 rpm within 5 minutes my overheat alarm went off even though it appeared the water pump was pumping water. I shut the engine off and waited 15 minutes, started it up and it ran o.k. at 2700 rpm. Any ideas of what the problem could be?
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Same thing here.
Gene: I have the same problem with my engine. One of the things that I noticed (and plan on correcting in the next couple of weeks) is the raw water intake on the thru hull is very small. I had a problem a few weeks ago. We had grounded the boat in the harbor during a low tide. While trying to get un-stuck we churned up the bottom and sucked in some gravel that plugged up the thru hull. The gravel never got to the strainer. When I removed the intake hose I noticed that the cast fitting where the hose fits is only about 1/4"-3/8". I am planning on drilling the fitting out and see if the additional water flow help this overheating problem. The other problem could be the prop. Assuming that your bottom and prop are clean and the mixing elbow is clear, you should look at the prop pitch. This has been discussed in detail but your engine is rated at a max of 3600 rpms. You should be able to pull 3600 when in gear at wide open throttle (WOT). If you cannot not and all of the other things are okay, you may be over-propped. Remember that the operating RPM's are based on the ability to get MAX rpms. I am going to have my prop re-pitch or replace my prop in the next few months. I would also like to hear Gordon's take on this issue too.
Gene: I have the same problem with my engine. One of the things that I noticed (and plan on correcting in the next couple of weeks) is the raw water intake on the thru hull is very small. I had a problem a few weeks ago. We had grounded the boat in the harbor during a low tide. While trying to get un-stuck we churned up the bottom and sucked in some gravel that plugged up the thru hull. The gravel never got to the strainer. When I removed the intake hose I noticed that the cast fitting where the hose fits is only about 1/4"-3/8". I am planning on drilling the fitting out and see if the additional water flow help this overheating problem. The other problem could be the prop. Assuming that your bottom and prop are clean and the mixing elbow is clear, you should look at the prop pitch. This has been discussed in detail but your engine is rated at a max of 3600 rpms. You should be able to pull 3600 when in gear at wide open throttle (WOT). If you cannot not and all of the other things are okay, you may be over-propped. Remember that the operating RPM's are based on the ability to get MAX rpms. I am going to have my prop re-pitch or replace my prop in the next few months. I would also like to hear Gordon's take on this issue too.
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Gordon Torresen
You should be able to run any engine wide open for long periods without overheating. You don't want to do it, unless absolutely required, for other reasons. Your engine temperature should increase until the thermostat opens allowing an increased amount of water to take away any generated heat. The temperature should vary slightly as the thermostat seeks the proper position. There should not be a continuous rise in temperature. We have fire in the engine water in the ocean and a system with which to use that water to carry away the heat of the fire. We have to move enough water. The sea water pump must be in good shape. The water passages must be clear. The heat exchanger tubes must be clean. The exhaust back pressure must be proper. Within the engine the circulating pump must be in good shape, the passages clear, coolant at the proper level, the surfaces that the coolant contacts must be clean, the water should have heat transferring enhancers and the heat exchanger tubes must be clean. There are probably more areas to think about but you get the idea. One or more of these items not being right could lead to your symptoms. The small hole in the seacock, as mentioned in another post could be to blame. A seawater pump impeller within the system from a previous failure could reduce the flow. ETC. You have to work through it, item by item, until you have found the answer. Sorry I can't be more precise.
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Gordon Torresen
Overheating Two
Sometimes I read my own stuff and find flaws. My last post dragged on about this overheating problem and dwelt mostly with the engine. Since the engine is designed not to over heat and since yours is properly maintained, the problem is more than likely external to the engine. Steve Dion's post about a small through hull may be a good place to start. At least its the kind of defect to examine. Sometimes high volume boat builders work at reducing cost in strange ways. If the 1/2" through hull works for a small engine, quantity buying might see it used when boat and engine sizes increase. The same holds for the exhaust system. The cooling water is discharged into the exhaust and if pipe sizes there are too small it meets the resistance of high pressure. Of course it could be that spare anchor that is sitting atop one of the hoses. The 3GM30F engines should have 5/8" hoses. That makes that the ID of the fittings should never be less than 1/2". In this application, bigger is better. I also digested your comment about shutting the engine down when it overheated. I recognize that the immediate response to an engine alarm should be to shut it down but if the subsequent evaluation shows it to be overheating, the engine should be restarted at an idle, external cooling water flow should be confirmed and, if it is there, the engine should be allowed to cool with the internal water circulating. The internal engine temperature actually jumps up when the water circulation is removed.
Sometimes I read my own stuff and find flaws. My last post dragged on about this overheating problem and dwelt mostly with the engine. Since the engine is designed not to over heat and since yours is properly maintained, the problem is more than likely external to the engine. Steve Dion's post about a small through hull may be a good place to start. At least its the kind of defect to examine. Sometimes high volume boat builders work at reducing cost in strange ways. If the 1/2" through hull works for a small engine, quantity buying might see it used when boat and engine sizes increase. The same holds for the exhaust system. The cooling water is discharged into the exhaust and if pipe sizes there are too small it meets the resistance of high pressure. Of course it could be that spare anchor that is sitting atop one of the hoses. The 3GM30F engines should have 5/8" hoses. That makes that the ID of the fittings should never be less than 1/2". In this application, bigger is better. I also digested your comment about shutting the engine down when it overheated. I recognize that the immediate response to an engine alarm should be to shut it down but if the subsequent evaluation shows it to be overheating, the engine should be restarted at an idle, external cooling water flow should be confirmed and, if it is there, the engine should be allowed to cool with the internal water circulating. The internal engine temperature actually jumps up when the water circulation is removed.
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Mark Johnson
Gordon...speaking of that...
I have the Yanmar 76hp turbo diesel on my boat. My cruising RPM is 3000. At that speed my temp is about 85C or 175F. It's hard to tell with the metric guages, but every once in a while I run it at full thottle which is 3700. I see the temp increase (hard to tell how much because of the guage), but how much of an increase would be normal? Thanks Mark Johnson
I have the Yanmar 76hp turbo diesel on my boat. My cruising RPM is 3000. At that speed my temp is about 85C or 175F. It's hard to tell with the metric guages, but every once in a while I run it at full thottle which is 3700. I see the temp increase (hard to tell how much because of the guage), but how much of an increase would be normal? Thanks Mark Johnson
Overheating 3
Gordon: This is exactly what we do. Check the exhaust flow first. Then we shut down the engine. We check to see that there is water circulating through the raw water strainer. If we have water intake, we restart the engine and run at very low RPM (1000-1500). Our theory on this was the fact that we now have water circulating through the engine. The alarm usually goes off in a mater of minutes. I was told by our Yanmar service group that the alarm is set so there really is no damage to the engine, just a warning that you are approaching a critical temp. We have had different overheating problems over the years, everything from minnows in the raw water strainer to the plugged intake at the seacock. To this I say, anyone that wants to add a water temp gauge should do it, but never but never remove the excellent alarm system that Yanmar built into these engines. A boat is NOT like a car. You do not have the instruments right in front of your face. The alarm is your failsafe.
Gordon: This is exactly what we do. Check the exhaust flow first. Then we shut down the engine. We check to see that there is water circulating through the raw water strainer. If we have water intake, we restart the engine and run at very low RPM (1000-1500). Our theory on this was the fact that we now have water circulating through the engine. The alarm usually goes off in a mater of minutes. I was told by our Yanmar service group that the alarm is set so there really is no damage to the engine, just a warning that you are approaching a critical temp. We have had different overheating problems over the years, everything from minnows in the raw water strainer to the plugged intake at the seacock. To this I say, anyone that wants to add a water temp gauge should do it, but never but never remove the excellent alarm system that Yanmar built into these engines. A boat is NOT like a car. You do not have the instruments right in front of your face. The alarm is your failsafe.
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Charles Weikel
Inlet water temp?
Doesn't inlet cooling water temperature effect all of this? Down in Louisiana Lake Ponchatrain is now at 88 degrees and it is easy to get a high temp alarm on my 2QM15 if I push it too hard.
Doesn't inlet cooling water temperature effect all of this? Down in Louisiana Lake Ponchatrain is now at 88 degrees and it is easy to get a high temp alarm on my 2QM15 if I push it too hard.
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Don
M-18 Overheat
I had the same problem with my engine overheating at cruise RPM (2560), but is fine at 2200. I installed a shutoff valve on the hose going to the water heater. (Available at auto parts store - CarQuest part # 277950. $14) Now all the coolant goes thru the heat exchanger with the valve closed. Max temp never goes above 183. Additional improvement is the engine reaches operation temp much quicker, so I can shut it down and hoist sails quicker. Also, less worry of a guest getting burned with 170 degree water at the sink. When I go cruising, I just open the valve.
I had the same problem with my engine overheating at cruise RPM (2560), but is fine at 2200. I installed a shutoff valve on the hose going to the water heater. (Available at auto parts store - CarQuest part # 277950. $14) Now all the coolant goes thru the heat exchanger with the valve closed. Max temp never goes above 183. Additional improvement is the engine reaches operation temp much quicker, so I can shut it down and hoist sails quicker. Also, less worry of a guest getting burned with 170 degree water at the sink. When I go cruising, I just open the valve.
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