engine alarm

[LAZ]

Greetings all. I have a first time issue which has my mystified. Hopefully someone can help. For the first time, when under load, my alarm goes off when my twin mercs reach 1600+ RPM. Then goes off when revs are decreased below 1600. Did this under test 3 different times. Yet when I checked bilges thoroughly with sniffer etc, there was no gas or vapor leak, which is what is supposed to engage the alarm. Anybody have ant idea what might be causing this? Thanks in advance for any help!

[Viper]

Are you talking about an "engine alarm" or a fume detector alarm? The two are different, one is warning you that there is something on the engine that needs your attention, and the other is warning that there are gas fumes in the engine compartment.

By some of your description, it sounds like the fume detector. The sensor modules don't last forever and will sometimes sound for no reason. It should also be noted there are other things that will affect them such as batteries gassing off. You can also get erratic alarms if the sensor got oily bilge water splashed on it. OR, it's sniffing fumes that you can't! If it's original equipment though, I'd say it's time to replace the system with a new one. It's a safety concern if it's not working properly.

Do you smell any exhaust down there?

[tomschauer]

if its the engine alarm(s), they are triggered by low oil pressure, high temperature engine and high transmission temperature.
If I had to take a guess, I would say you are tripping on high engine temp since it happens when you are loading the engines. When was the last time you replaced the impellers?

If indeed it is a fume detector, refer to vipers comments.

[Viper]

Qr Bbpost if its the engine alarm(s), they are triggered by low oil pressure, high temperature engine and high transmission temperature.
If I had to take a guess, I would say you are tripping on high engine temp since it happens when you are loading the engines. When was the last time you replaced the impellers?

If indeed it is a fume detector, refer to vipers comments.

+1

[bud37]

Just to add to the previous....fume detectors are looking for explosive gases , examples are gasoline fumes, propane gas, hydrogen from off gassing batteries etc....except for the hydrogen which is lighter than air, both the gasoline and propane fumes are more dense than air so they will be located in the lowest part of the bilge, that is where the detector sensor should be. They are set to alarm at around 20 % of the LEL ( lower explosive limit ), long before there is enough concentration for ignition.

Exhaust fumes on the other hand will only set one of those off if the engine is poorly tuned ( running rich ) to the point of raw gas in the exhaust fume and you have an exhaust leak in the compartment.

Like has been said it is very important you figure out what alarm you are hearing so you are safe here.

[LAZ]

Thanks guys for all guidance. Pretty sure it is just a gas and propane leak and battery issue detector, but I could find no evidence of any. If it is a faulty sensor issue, does it make sense that they would only go off over 1600 RPM? Don't believe I have a specific "engine" alarm, but will check manuals.

[bud37]

Just remember previous owners could have installed anything down there, so a real good look is in order. Look for wires going to the exhaust hoses near clamps, follow all the wiring you can find in the bilge area etc.

Do you have inboards with shafts or inboard outboard I/O type propulsion.

Fume alarms are not tied to any engine performance, they just monitor and alarm.

[waybomb]

Is the sensor next to incoming air ducts? Maybe the wind at 1600 rpm is enough to set off the sensor.

I have a refrigerant leak detector, and if you blow lightly on the sensor, the thing beeps as if refrigerant is present. I can assure you, I do not create refrigerant in my lungs.

[bud37]

Qr Bbpost I do not create refrigerant in my lungs.

But you do exhale CO2 among other things..... ....that leak detector may pick that up based on refrigerant make up.

[tomschauer]

An ultrasonic leak detector detects the sound of the leak not the refrigerant itself.