Engine Alarm

[scottwvyc]

After starting my 671N 's today on a 37C, the stbrd engine alarm started to go off. The PO added raw water flow alarms that I assume are wired into the standard Hatteras engine alarm. Good oil pressure, I cleaned the raw water strainer, which was really plugged up, and I thought for sure this was going to fix the problem, but the alarm persisted. This is the same alarm that sounds when I turn on the key to start the engines and stops ringing after the engine fires. Could there be a problem with the alarm not recognizing the engine has started? Any ideas would be appreciated. Thanks Scott

 

[Jim saco]

On my 41c the system has all normally open sensors and they close on alarm. If you assume It's your raw water flow then remove the wires and ring across the two terminals. If you have a short between the two you've found the cause of the alarm. If its open keep searching. There are quite a few sensors on my 6v92's. Oil pressure fuel pressure coolant temp and exhaust temp are a few off the top of my head. Keep checking each one until you find which sensor it is.

Good luck

 

[GJH]

Gotta know what you got. On a lot of boats, including mine, many of the sensors are normally closed. The alarm the OP described, (comes on when ignition key is turned, goes off when engine up and running) is usually the oil pressure alarm. You don't have a systems monitor with lights to indicate alarms? What do your oil pressure gauges read?

 

[Genesis]

If your boat has all the alarms "ganged" so any one sets them off with no indication which is the culprit I'd first find the cause of the alarm and then immediately fix that problem.

Not knowing why you have an alarm can be quite dangerous when it doesn't happen in a convenient place (e.g. while running an inlet.)

 

[MikeP]

As noted, the oem alarm that comes on when you turn on the key and goes off (hopefully) after the engine starts is Oil Pressure. But since you said the oil pressure gauge readings are OK, it could be a failure of the alarm sys oil pressure switch OR the circuitry in the alarm system itself. It would be good to connect a manual gauge oil pressure gauge just to verify that pressure is OK. Does the alarm stop sounding if you raise engine RPM a bit?

Of course, the same thing could be true of the added RW alarms - could be a sensor problem or some issue in the alarm system itself. I assume you have actually checked the water flow from the exhaust/compared it to the "good engine's" flow to verify that it is normal.

If the oil p is ok and the water flow is ok, then it's pretty likely to be a sensor/wiring/alarm box issue, not an engine issue.

 

[fissioneng]

As noted, the oem alarm that comes on when you turn on the key and goes off (hopefully) after the engine starts is Oil Pressure. But since you said the oil pressure gauge readings are OK, it could be a failure of the alarm sys oil pressure switch OR the circuitry in the alarm system itself. It would be good to connect a manual gauge oil pressure gauge just to verify that pressure is OK. Does the alarm stop sounding if you raise engine RPM a bit?

I had this happen to me last fall. Boat had been idling at the dock for 30 minutes and the engine alarm went off. Gauges all looked fine. When I raised the rpm, it went away, so I instantly thought it was the oil pressure alarm switch. Unfortunately, I couldn't reproduce it later. I took off the switch leads and cleaned them up, then reattached. Still no recurrence.

Mine is a NO system.

 

[ncfathom]

Not on my mains but, the alarms on the genny have reset buttons after the problem is repaired.

 

[scottwvyc]

First off, thanks to everyone for your replies, they were really helpful. I have found the culprit! The raw water flow out of the exhaust seemed to me to be less than what I am used to seeing, The boat has a slight list to port so it is difficult to compare the flow port to starboard. I pulled the plate on the raw water pump and sure enough the impeller is in bad shape. I didn't have a puller on board, and it wouldn't slide out easily with screwdrivers, so I haven't had a close look at it, but there are, at least parts of vanes missing. Where is the first place I should look to try and find the missing pieces? Also, I would be grateful for any tips on reinstalling the new one, I am an impeller virgin. I will replace the port side at the same time. Many thanks, Scott.

 

[SKYCHENEY]

Lube up the new impeller to slide it in. I usually just use dish detergent. I also put a plastic wire tie on it to compress the vanes to get it to start to slide in. Once started you can cut the tie.

Take a look at the cover plate. If worn excessively, flip it over upon reinstallation or replace.

 

[MikeP]

"Where is the first place I should look to try and find the missing pieces? "

The impeller pieces should be on the input side of the heat exchanger on an N engine, clogging up some of the passages!

 

[GJH]

Beware: sometimes when you think you have found "the" problem, all you actually have done is find another problem, and other times just a subset or consequence of the "real" problem. Happened to me again just today cleaning up an electrical issue.