I have a '92 model that has a recurring overheating--at least apparent overheating--problem at full throttle. First, this engine has been babied with frequent oil & filter changes (Chevron Delo 30w & Yanmar filter), the exhaust elbow is two years old, and the cooling system has been flushed regularly. Under normal conditions I run the engine at 2,800-3,000 RPM, and there is no problem. Occasionally I run it to 3,200 again with no problem. At full throttle I get 3,400 rpm and after 5 minutes (with the engine already at op temp) the overheating light and buzzer come on. At this point I throttle down to about 2,000 and the buzzer goes out after 30 secoonds and the engine runs fine. This is the second time its happened. Any suggestions?
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Pete Vente
Overheating ...
Optimal cruising rpm is 80% of max, so I wouldn't worry too much about the overheating. In any case .... Is there any white smoke (steam) coming out of the exhaust ? If there is, I would bet that it is your exhaust elbow causing the problem, even though it is only two years old. Depending upon usage, these should be cleaned out/replaced every few years anyway. Another reason may be insufficient flow of raw water, whether restricted or just not enough volume to sustain 3400 rpm.
Optimal cruising rpm is 80% of max, so I wouldn't worry too much about the overheating. In any case .... Is there any white smoke (steam) coming out of the exhaust ? If there is, I would bet that it is your exhaust elbow causing the problem, even though it is only two years old. Depending upon usage, these should be cleaned out/replaced every few years anyway. Another reason may be insufficient flow of raw water, whether restricted or just not enough volume to sustain 3400 rpm.
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Steamer
Engine Overheat
On my 29.5, I've had problems with the intake screen plugging because of eel grass and other debris in the water. After overheating the first time and activating the alarm, I now do a regular check of the filter, especially in weedy waters. My filter is beside the salt water intake shutoff under the aft cabin bed. I don't know if this applies to the 33.5
On my 29.5, I've had problems with the intake screen plugging because of eel grass and other debris in the water. After overheating the first time and activating the alarm, I now do a regular check of the filter, especially in weedy waters. My filter is beside the salt water intake shutoff under the aft cabin bed. I don't know if this applies to the 33.5
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D. Grosz
My thoughts
There is no smoke or steam of any kind. My gut sense is that the total volume of water may not be enough at that RPM. Perhaps the speed of the boat at that RPM is causing bubbles near the water intake? Or maybe the size of the intake/hoses not large enough or the impeller is somehow malfunctioning (perhaps a blade damaged? although I've replaced the impleller recently as well). It could possibly be that the heat exchanger may need an internal cleaning/flush. And I'll double check the intake screen. Its not much of a concern at this point but I'd like to resolve it anyway.
There is no smoke or steam of any kind. My gut sense is that the total volume of water may not be enough at that RPM. Perhaps the speed of the boat at that RPM is causing bubbles near the water intake? Or maybe the size of the intake/hoses not large enough or the impeller is somehow malfunctioning (perhaps a blade damaged? although I've replaced the impleller recently as well). It could possibly be that the heat exchanger may need an internal cleaning/flush. And I'll double check the intake screen. Its not much of a concern at this point but I'd like to resolve it anyway.
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Walt G.
Have the Right Sender?
My problem with "overheating" was the sender. My 3QM30 was originally salt-water cooled, converted with an aftermarket SenDur heat exchanger to fresh water operation. The sender for a salt water cooled engine is set to go off at a lower temp than a fresh water cooled engine. Replacing the sender with a higher temp one fixed the "overheat" problem.
My problem with "overheating" was the sender. My 3QM30 was originally salt-water cooled, converted with an aftermarket SenDur heat exchanger to fresh water operation. The sender for a salt water cooled engine is set to go off at a lower temp than a fresh water cooled engine. Replacing the sender with a higher temp one fixed the "overheat" problem.
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Bryan C.
Thermostat?
A malfunctioning thermostat is a possibility, tho' unlikely. If the thermostat is not opening all the way or at the right temp could cause overheat. Test by pulling it and put in a pan of heating water with cooking thermometer.
A malfunctioning thermostat is a possibility, tho' unlikely. If the thermostat is not opening all the way or at the right temp could cause overheat. Test by pulling it and put in a pan of heating water with cooking thermometer.
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Gordon Torresen
Overheating
You state that you have the 3GM30, a sea water cooled model. Also, since 1993, there has no doubt been a gradual degradation of the cooling water system. You should be able to run the engine wide open forever without overheating (although there are many other reasons why you shouldn't). There could be a build-up within the engine block that is insulating the heat from the cooling water. There could be that missing impeller blade from a previous impeller failure. There could be wear on the end plates of the water pump or on its cam. Your speculations on hoses and other variables are all valid. Although not a problem now, the symptoms portend greater problems on the way.
You state that you have the 3GM30, a sea water cooled model. Also, since 1993, there has no doubt been a gradual degradation of the cooling water system. You should be able to run the engine wide open forever without overheating (although there are many other reasons why you shouldn't). There could be a build-up within the engine block that is insulating the heat from the cooling water. There could be that missing impeller blade from a previous impeller failure. There could be wear on the end plates of the water pump or on its cam. Your speculations on hoses and other variables are all valid. Although not a problem now, the symptoms portend greater problems on the way.
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