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post #1 of 13 Old 07-08-2007 Thread Starter
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Overheat situation

I noticed two things on the boat today when we powered to the pumpout:

1) The tach wasn't working. Eventually I found a split alternator belt in the bilge. Bummer, but not critical.

2) The water/coolant temp hit 230 F. I noticed this AFTER docking. I shut the engine down and noticed that the expansion tank had shed some coolant into the bilge. I took apart the primary water filter (a Perko basket in a glass type), and blew out the engine intake hose. I also took off the cap to the standpipe to make sure a fish hadn't met an unfortunate end in there...it hadn't. Aside from a bit of stray vegetation and "bits", I found nothing amiss.

After the engine had cooled, I started it again and noted that the output appeared normal, i.e. plenty of gush out the exhaust. The engine took five minutes to reach its customary 170 F or so of coolant temperature. All seems well.

My questions are these: I assume that it is possible I sucked in partially a plastic bag or some more rigid obstruction in the standpipe...it currently lacks a screen and is just a three inch hole in the bottom of the boat. Said mystery blockage caused the overheat and when the motor was stopped, it dropped to the bottom or floated away unseen. Thoughts?

Second possibility is a cacked vane on the impeller, which is new this season. I can't discount this without dissembling the raw water pump, which is a pain in the ass, but will have to be done if this issue persists. As I said, output at dock seems normal (spurt, gurgle, spurt), the lines are visibly clear, the filter is clean and the standpipe holds no dead fish (you can see the water all the way down with the cap off!)

Advice, theories, conspiracies are welcome. Right now, I assume I just have to source a 44 inch alternator belt tomorrow morning to continue my sail.
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post #2 of 13 Old 07-08-2007
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Yes, that sounds pretty plausible. Some types of seaweed can also cause that kind of problem. I would highly recommend putting a grill over the three-inch hole that feeds the standpipe. That will stop some of the larger items from clogging the intake.

I doubt it is a cracked impeller blade. At some point in the future, I would try and change the water pump out for a design that doesn't require you to disassemble the pump to get to the impeller.

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post #3 of 13 Old 07-08-2007
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Val,
The obvious question that comes to mind is; does the alternator belt also turn the water pump?

“Scientists are people who build the Brooklyn Bridge and then buy it.”
Wm. F. Buckley, Jr.
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post #4 of 13 Old 07-09-2007
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Sailaway-

I don't think so, since it doesn't sound like he's replaced the belt yet, and the engine isn't overheating now... just for that brief period of time. Many water pumps are mechanically driven by the engine directly, rather than driven via a belt.

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post #5 of 13 Old 07-09-2007
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Valiente - The belt does not turn the raw water pump, but it does turn the coolant/water pump. That would explain why you had the extra coolant in the overflow reservoir. The engine overheated due to the coolant not being circulated, not the raw water. My bet would be that your raw water systems are fine, it was the coolant system that caused the overheat and you fixed the problem already. If it persists and you get too much coolant in the reservoir again, it may be the thermostat. How bad is the belt, is it slipping, did you replace it?
PS. It could also be blockage like you said. If your impeller was bad it would keep overheating.

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Last edited by bestfriend; 07-09-2007 at 02:39 AM.
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post #6 of 13 Old 07-09-2007
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It sounds to me like the belt. That would also account for the tach not working.
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post #7 of 13 Old 07-09-2007
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The tach would not have worked with the belt off because it is driven by the alternator which is one place we know that the belt went too......
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Quote:
Originally Posted by sailaway21
Val,
The obvious question that comes to mind is; does the alternator belt also turn the water pump?
No, but I can see you've had your coffee this morning! The raw water pump (the stock Sherwood F-85) is driven by a cam in the block. The PTO to alternator belt is a 44 inch x 1/2 "toothed" type I am trying to source locally this morning.

The water/exhaust gases output at the exhaust outlet seems normal.
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Quote:
Originally Posted by bestfriend
Valiente - The belt does not turn the raw water pump, but it does turn the coolant/water pump. That would explain why you had the extra coolant in the overflow reservoir. The engine overheated due to the coolant not being circulated, not the raw water. My bet would be that your raw water systems are fine, it was the coolant system that caused the overheat and you fixed the problem already. If it persists and you get too much coolant in the reservoir again, it may be the thermostat. How bad is the belt, is it slipping, did you replace it?
PS. It could also be blockage like you said. If your impeller was bad it would keep overheating.
Hmm. I am not sure how the coolant circuit pump would be driven off the belt, unless it was somehow an electrical pump and it was powered directly from the alternator.

I am sourcing the belt from home this morning...the shop manual is back on the boat. I will put on a new belt before I go anywhere regardless, just for the charging factor, but if the coolant pump is powered by the alt (or has otherwise failed) this would definitely be an issue to investigate. Thanks.
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post #10 of 13 Old 07-09-2007 Thread Starter
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Quote:
Originally Posted by essman
The tach would not have worked with the belt off because it is driven by the alternator which is one place we know that the belt went too......
Yep. No belt, no tach. Now to figure out if the lack of a turning alternator affected the movement of coolant through the block.
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