Having just posted a response to a hot-running diesel engine made me come up with this question. How large is the intake valve on your Hunter? My engine (3HM35F) has an intake thru-hull that is about 1/4" in diameter. The nipple into the intake hose is actually 1/4" and the hose leads to the strainer. It provides enough water for cooling until something gets sucked in and partially clogs the intake. Most commonly will be eel grass that cannot make it by the 90 degree elbow at the intake. If it makes it thru that elbow, then it has to make it past the elbow at the strainer. These elbows don't have a radius curve, just a straight 90 elbow. But back to my question - How large is your cooling input stream to your engine? Is it enough?
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Noel Black
replaced 1/4 inch thru hull
While troubleshooting engine overheating one thing I noticed was the cooling thru-hull had a very narrow opening, internally about half the 1/2 inch fitting. I switched with the head intake and later replaced the thru-hull with a 5/8inch. I also removed and later replaced the thermostat. The problem went away so do not know what was the cause. I doubt it was the intake but the narrow opening appeared to defeat the purpose of the 1/2 inch hose.
While troubleshooting engine overheating one thing I noticed was the cooling thru-hull had a very narrow opening, internally about half the 1/2 inch fitting. I switched with the head intake and later replaced the thru-hull with a 5/8inch. I also removed and later replaced the thermostat. The problem went away so do not know what was the cause. I doubt it was the intake but the narrow opening appeared to defeat the purpose of the 1/2 inch hose.
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Paul Akers
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Steve O.
not enough
I was told by a very knowledgable person who works on Yanmars for a living that the intake thru-hull fitting is not large enough and can be a source of overheating at high rpm. Retrofitting to a larger diameter certainly won't hurt anything if done properly.
I was told by a very knowledgable person who works on Yanmars for a living that the intake thru-hull fitting is not large enough and can be a source of overheating at high rpm. Retrofitting to a larger diameter certainly won't hurt anything if done properly.
Cut off the end of the hose barb.
Paul: I have had gravel get caught in the raw water intake (shoal harbor entrance). I started to overheat after the engine ran for about 10 mins. We turned around and removed the strainer only to find that we had NO water flow. When I removed the hose to the valve there was small gravel stuck in the hose. I just used a piece of stiff wire and cleared the opening. When I looked at the hose barb that was attached to the valve I noticed that the opening was VERY small. Now that you brought this up, I think I am going to use a dremmel tool with a cut off blade and cut off the top of the hose barb. This will probably double the amount of water flow. Thanks for bringing up the subject, I had really forgotten about the problem.
Paul: I have had gravel get caught in the raw water intake (shoal harbor entrance). I started to overheat after the engine ran for about 10 mins. We turned around and removed the strainer only to find that we had NO water flow. When I removed the hose to the valve there was small gravel stuck in the hose. I just used a piece of stiff wire and cleared the opening. When I looked at the hose barb that was attached to the valve I noticed that the opening was VERY small. Now that you brought this up, I think I am going to use a dremmel tool with a cut off blade and cut off the top of the hose barb. This will probably double the amount of water flow. Thanks for bringing up the subject, I had really forgotten about the problem.
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Jon petersen
Replaced with 1" Thru-hull on 33.5
I was having over heating problems and replaced the 1/2" thru-hull with a 1" full flow..this uses a 1 1/4" hose... and a 1" straner.. over kill but the Florida grass was blocking the intake every day... It did make the water temp come down at the same RPM.. Engine is the 3GM30F.. By the way the heating problem was the heat exchanger.. I was using the Green antifreeze and it had a slime build-up...Salt water side was clean..
I was having over heating problems and replaced the 1/2" thru-hull with a 1" full flow..this uses a 1 1/4" hose... and a 1" straner.. over kill but the Florida grass was blocking the intake every day... It did make the water temp come down at the same RPM.. Engine is the 3GM30F.. By the way the heating problem was the heat exchanger.. I was using the Green antifreeze and it had a slime build-up...Salt water side was clean..
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J. Tesoriero
I had the same question.
I have a smaller engine, 2QM15, but also noticed that the raw water thru hull was on the small side and easily blocked by small amount of eel grass or debris. Guided by the fact that the inlet on the raw pump takes only a half inch diameter hose, I replaced everything from the thru hull to the engine with 3/4 inch ID components. I have not had an overheat problem since.
I have a smaller engine, 2QM15, but also noticed that the raw water thru hull was on the small side and easily blocked by small amount of eel grass or debris. Guided by the fact that the inlet on the raw pump takes only a half inch diameter hose, I replaced everything from the thru hull to the engine with 3/4 inch ID components. I have not had an overheat problem since.
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Paul Akers
Thanks everyone for the advice
I've been suspect of the size of the intake for a few years. It easily handles 1 or two strands of eel grass at a time, but not much more. I've lived with it until this summer when I was sailing in Maine. This year, Casco Bay has an incredible amount of eel grass and rock week floating in the bay. When I was warming up the engine or slowly negotiating a channel or river, it woulg suck up and obstruct the intake, thereby reducing the flow. Now I have a winter project to put on the list.
I've been suspect of the size of the intake for a few years. It easily handles 1 or two strands of eel grass at a time, but not much more. I've lived with it until this summer when I was sailing in Maine. This year, Casco Bay has an incredible amount of eel grass and rock week floating in the bay. When I was warming up the engine or slowly negotiating a channel or river, it woulg suck up and obstruct the intake, thereby reducing the flow. Now I have a winter project to put on the list.
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