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post #1 of 37 Old 02-04-2007 Thread Starter
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overheating kubota

oops.....sorry in advance for the double post

hi, any thoughts on this one? i have a kubota 22hp, which had been operating flawlessly for the last 6mths. suddenly its started the following traits- it will run great for about an hour at 2500rpm, engine pressure ok, temp ok, water out the exhaust ok, then for some reason, oil pressure drops, temp goes up, and the engine overheating alarm goes off. i shut the engine off for about 15minutes, then everything is fine again until the next occurence. any suggestions?
btw how do i put that radiator anti corrosion stuff in my engine? do i just add it directly to the radiator w/ some water?

sorry for asking what may be a dumb question. thank you
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post #2 of 37 Old 02-05-2007
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Do you know if you have a open system or a closed system ? I see you mention a radiator, but it sounds like your not sure if you have one.
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post #3 of 37 Old 02-05-2007
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mrkeith,... how old is the engine, when was the engine last serviced and what was done. Does this happen at a lower rpm when operated for the same length of time?

....radiator? anti-corrosion? .... are you asking about coolant in the fresh water tank? or about a cleaning agent to remove mineral build up in the heat exchanger?

Have you checked the basics to ensure that the amount of water flowing to the engine has not changed? i.e. clean strainer and through hull, the sea water hose is not restricting flow, impeller blade(s) in the system. Is the fresh water side filled with coolant/water, are you having to refill after running the engine for a while?

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post #4 of 37 Old 02-05-2007
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one word:

Thermostat
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post #5 of 37 Old 02-05-2007 Thread Starter
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sorry i wasnt more specific. the engine has a radiator and a fresh water heat exchanger, so there is a closed fresh water system that runs through the engine and an open system that runs through the heat exchanger to cools the fresh water. the radiator has recently been topped up and the oil has recently been changed. i changed the impeller a while ago (3 weeks) and noticed that some of the blades were broken off. the specific engine is a kubota d950. thank you
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post #6 of 37 Old 02-05-2007 Thread Starter
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also, the engine was new in 98, and i don't think they ever used coolant other than fresh water in the radiator. there is a bottle of radiator anti corrosion liquid in the boat, i guess i m not sure if that is suppose to be put in the radiator or its suppose to only be used to flush the radiator. the over heating used to happen at the lower rpms after the engine had run for a couple hous, but after i changed the oil it seemed to be ok up until this most recent incident. again, we were monitoring the engine temp and oil pretty religiously and it was fine until all of a sudden it went hot and the alarm went off. thanks again for all the info/help
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post #7 of 37 Old 02-05-2007
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OK,... First, something caused the impeller to fail, overheat and loose some of the blades. What happened? Has it been corrected?

Second, did you account for all the blades that were missing? Is it possible that a blade is disturbing the flow rate of the s/w. Is the input side of the heat exchanger clean of debris from the impeller?

Third, go to NAPA and pick up a gallon of diesel engine coolant, some come premixed others you will need to mix with DISTILLED water. Replace the fresh water with the coolant. Make sure you bleed the engine's fresh water system at the highest level, run and monitor the level, top off if necessary.

... let us know.

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post #8 of 37 Old 02-05-2007
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"i changed the impeller a while ago (3 weeks) and noticed that some of the blades were broken off. "

Mrkeith...did you find those broken off impeller blade pieces? My guess is they are lodged in your heat exchanger and restricting flow.
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post #9 of 37 Old 02-05-2007
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My guess would be no... he didn't fish out all the broken impeller pieces...

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post #10 of 37 Old 02-05-2007
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Add my vote to impeller pieces being stuck in there someplace and clogging the flow. If you can't see them, you can try hooking up a hose and backflushing the engine coolant passages to try driving them out. (If nothing comes out, also try removing the impeller to do this.)

This is the main reason impellers are "supposed" to be replaced every year as preventive maintenance, so blades that eventually do break off won't cause blockages.

The antifreeze for your engine isn't just there to stop it from freezing, there are also usually water pump lubricants and other compounds in it, so while folks may argue about what is best, running AF instead of water is pretty much always a better way to go.

I'd be somewhat concerned about the oil pressure drop though. Oil actually cools the cylinder walls, and then transfers the heat to the rest of the block and the coolant system. Check your oil level and then try to confirm if the oil pressure gauge is bad (it can happen) or why you really have low oil pressure (often just a failed pressure regulator spring in the oil pump).

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