Sensor not Sender.....

[Top Shelf]

So we've got a constant Stb Engine alarm on (1989 8v92, Covington, Boat is a 48' CNV). Engine, gear, EGT are all fine. Gauges
indicate everything is happy.

Spoke with Les Henderson (really good and gracious guy) about trying to figure out where to start on the debug.
Where in the Hatt alarm system is the anomaly. We got into this discussion about Senders and Sensors.
All the connections I am familiar with (and I thought I knew these engines pretty well) seem to be senders for
the gauges on the bridge.

Les indicated the Sensors (not the Senders) are separate dedicated components for the alarm system
only. Typically a rubberized black top and only two leads. They should all be daisy chained together on the engine,
Water temp, oil pressure, gear temp, etc......

I've never seen them......anyone familiar with 8v92's and these "sensors"? Heading to the boat tomorrow and a little
directional guidance would be most appreciated. Thank you.

 

[dottieshusband]

I would not assume everything is good. It is possible to have a point temperature spike in the area of the sensor. For example, there is a 205' temperature alarm sensor in the water manifold, and also a temp gage sending sensor. On my boat, they are on opposite ends of the manifold. So, a leaking blower seal over fuels the cylinder in the area of the 205' alarm, and you'd get the audible alarm, but the gauge sender is 3 cylinders downstream in the coolant flow, so the temp shows good on the gauge. Not knowing a lot about your engine, if it was me, I'd swap the sensors to eliminate that as a cause.

 

[saltshaker]

Couldn't agree more with the above post

 

[krush]

Meh, realistically it is just semantics. A sender probably technically is called a transducer or transmitter.

 

[SKYCHENEY]

Start at the 12pt monitor board. That is probably where the problem lies, so if you jumper the offending alarm wires at the board and the alarm doesn't quit, the board is the problem. If it goes off, then its in the wiring or the sensor. Don't assume its a bad sensor without testing or you'll be buying sensors that you don't really need (don't ask me how I know).

Since it alarms all of the time, even with a cold engine, you can probably assume its not really a heat problem.

My money is on the main board if its original and you haven't had it worked on before.

 

[RonNP]

Who do you recommend to work on the 12 point monitors? Mine works with the lights going off if something is not correct but the audible alarm has quit. I was under the assumption nobody really worked on these systems anymore.

 

[dottieshusband]

I guess I'm not a good reader...if you get the alarm, even with the engine not running, it's a different diagnostic ballgame. I've gotten alarms due to low voltage and bad sensors at times.

 

[racclarkson@gmail.com]

The audible alarm is available at Radio Shack, exact fit. You can unscrew it and take it for a match. I'm hard of hearing, so mine can be heard over the engines two counties west of here.

I would not start at the panel. There's a lot of delicate stuff in there.

The sensors (disc type), if like mine, are normally closed circuits. Heat will trigger the metal disc to expand and break the circuit causing the alarm to light up and audible. If all else seems normal, you can bet it's a loose wire. Tie the two leads together and see if the alarm silences. You can also check the sensor with an ohm meter and a propane torch; the heat will break the circuit.

If the unit is bad, it can usually be repaired even if the contact points are gone. I'll be glad to detail that procedure if it'd help. Might take an hour or two, but the cost is about zero. Plus, it feels good to fix something rather than just replacing parts.

 

[SKYCHENEY]

Flight Systems used to repair the main boards:

http://www.flightsystems.com/

 

[SKYCHENEY]

I guess I'm not a good reader...if you get the alarm, even with the engine not running, it's a different diagnostic ballgame. I've gotten alarms due to low voltage and bad sensors at times.

The boards are very sensitive to low voltage and that can cause false alarms.

 

[racclarkson@gmail.com]

Originally Posted by dottieshusband
I guess I'm not a good reader...if you get the alarm, even with the engine not running, it's a different diagnostic ballgame. I've gotten alarms due to low voltage and bad sensors at times.


The engine does not have to be running to get an alarm (ex: hi exhaust temp). The ignition circuit ON is all it takes. A bad connection (broken wire, etc.) will trigger the alarm. Could even be intermittent with a loose connection.