Loss of Tach & Overheat Squeal @ low RPM - SailNet Community
 
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post #1 of 3 Old 10-27-2010 Thread Starter
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Loss of Tach & Overheat Squeal @ low RPM

I'm not sure if these two are related but I figured I's throw them out there. After getting my Columbia 31 out of dry dock the tach ceased to work. A friend of mine said that turning the key off before chocking the deisel off caused a surge and probably fried the diode in the alternator, thus killing my signal to the rpm gauge. Could this be right? Anybody had experience with this?

Also, before dry dock I would start my 2GM every day and run it at idle for about 30 minutes. When I did this I got the normal signal for overheat until about a second after I started it. Then it would remain at idle - quietly. After dry dock, idle speed had to be increased a bit to turn off the squeal. Now that I am home, from start (can't be overheating that fast) the signal goes off and it seems like I am having to use higher rpm to eliminate it. We added a dripless, but surely it is not robbing that much water from the water line. This engine gets regular maintenance and fresh antifreeze. I really think it is something other than overheating. Any deas?

Bones
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post #2 of 3 Old 10-27-2010
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Loss of Tach.
On a friends boat we had to have the alternator rebuilt after we fried the diodes by setting up the batteries incorrectly. I re-installed the alt. which has a wire running to the tach. That wire connection was done in a shoddy way by me and disconnected rendering the tach. useless. I had to make a proper connection and the tach. worked fine.
Squeal from engine.
Find out where the squeal is coming from. It is probably one of the water pumps, the alt. or the alternator. They all have bearings around shafts that spin that eventually fail and will create a nasty sound and need to be replaced.
Idling your diesel.
I'm not an expert by any means but I have read a great book by Nigel Caulder ('Boatowners Electrical & Mechanical Manual'). Everything I have read indicates that diesels like to be run at WOT (wide open throttle) or close, while under load so they get up to operating temperature rather then idling them where they do not get as hot. A hot diesel is a clean burning diesel whereas a cool idling diesel is likely to have incomplete combustion in the cylinders. You don't have to run the engine at WOT to get the temp up but you are supposed to have it under load, ie., either in forward or reverse, not in neutral.
Stuffing boxes.
Dripless or traditional require water in the shaft log for lubrication. This could also be the source of your squealing sound. Make sure your neutral gear is fully engaged and the shaft is not spinning if running 'on the hard'/drydock.

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post #3 of 3 Old 10-28-2010
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Quote:
Originally Posted by Blackwater View Post
...before dry dock I would start my 2GM every day and run it at idle for about 30 minutes. When I did this I got the normal signal for overheat until about a second after I started it. Then it would remain at idle - quietly. After dry dock, idle speed had to be increased a bit to turn off the squeal. Now that I am home, from start (can't be overheating that fast) the signal goes off and it seems like I am having to use higher rpm to eliminate it. We added a dripless, but surely it is not robbing that much water from the water line. This engine gets regular maintenance and fresh antifreeze. I really think it is something other than overheating. Any deas?

Bones
At start-up, the only alarm one normally hears is the low oil pressure warning since the cooling water temperature is not hot and would not close the temperature switch. Check you oil to ensure you've got it topped up properly and insure you have a clean oil filter. Your oil pressure is dependant upon the engine speed and a dirty filter can somewhat restrict flow which may be triggering your alarm.

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