Engine alarm going off, but no idea why?

[mikeauton]

My alarm is sounding, but the engine is running at normal temperature and oil pressure is where it should be? I checked the oil level and that is OK. Just wondering what else could cause the alarm to sound? Possibly a faulty thermostat?

Does anyone know precisely what failure points will trigger the alarm? This may enable me to narrow the field a little.....I know for sure it is nothing to do with my water pump as I only just fixed that.

 

[skydiveD30571]

Mike, on your engine you have:

Oil pressure, engine water temp, and 2 exhaust temp sensors (one for each riser). These are alarm switches, not the oil pressure and water temp senders that are displayed on your gauges. Your best bet is to just unhook each one-by-one until the alarm silences, then you know that's the switch that is tripping the alarm. If your oil pressure and water temps look normal as well as your exhaust elbows staying relatively cool, it will just be a faulty switch.

Here is a diagram of your sensors and senders. You're looking for #19 and #22, and 2 different #23's (one on back of each exhaust elbow). They have a tan wire with black stripe coming from them. http://www.marinepartseurope.com/en/volvo-penta-explodedview-7746090-30-10100.aspx

 

[mikeauton]

Thanks Skydive, the diagram is useful. I am pretty confident this is simply a faulty sensor, though I fired it up again yesterday and the alarm had stopped sounding.

Definitely do not have oil pressure or temperature issues, also I over hauled the risers in February when I had her out of the water.

Nice to know I can silence the alarm in future/narrow down by unplugging one of the four sensors. Had to bring the boat back in on a very busy weekend with my head over the windscreen to try and drown out the whine of my alarm Not a fun experience.

 

[skydiveD30571]

Those sensors are just simple resistor-type mechanisms that ground out when a calibrated temperature (or pressure) is reached. So when one starts to go bad, it can be intermittent. The wire is just a spade terminal and pops off easily, so next time you hear the alarm it should be easy to diagnose. The sensors are easily replaced too with a socket or wrench.