Gas fume detector goes off after idling for a while

[VicB]

Hi guys,
My wife and I are new to larger boats and just purchased a 88' 3807. We noticed when idling at a stand still for any length of time that our Gas Fume Detector goes off. Its an older Scentry 415. We thought it was the CO detector because when out on our first cruise we did open the back door several times to get stuff and adjust the radio, and when we docked we smelled exhaust in our clothes when we got home. Turns out after exploring the engine compartments, I found the sensor mounted to a starboard stringer. It only would go off when idling while not moving. Put it in gear it would go off. I did also find that the starboard bilge fan closest to the sensor had its duct separated and laid off to the side, so it was ineffective. Did not notice any smell other than just a general mechanical smell. The bilge will be cleaned up soon, but its pretty clean already. Any thoughts? Should this be a concern or could it ba a combo of old or dirty sensor and inop'd exhaust fan???

Thanks,
Vic

[bud37]

The fume detector senses raw gasoline fumes or other explosive fumes.....now if they are still in business I might check with them on their sensor life. Generally they throw an alarm as the device is turned on and does its self check then should be quiet unless it picks up something. Maybe see if you can find a manual for it.
Have a close look and feel all your fuel lines and connections to make sure they are dry, don't just assume the sensor is old and defective. Any alarm is a concern and needs to be followed up on, especially the explosives one.
Really the fume detector should not alarm at any time after the self check ....it will only do so in the presence of an explosive fume. Geez I hope this helps and be careful, If this confuses the issue further say so as this is important in my opinion.

Actually if you are not comfortable with this , it may be something to get an experienced person to check for you.

One more base to cover, by any chance do you have any propane stored anywhere onboard ?

[VicB]

It makes perfect sense. I understand how seeing if the alarm is valid first then working your way down to nuisance issues is the right way to go. When we bought the boat, the owner had all the oil changed and any preventative maintenance done by the marina mechanics a few days before our sea trial. This last week end, I found the old cardboard media type fuel filter laying under the engine. Possible there is enough residue left that the sensor was getting a sniff of that every once in a while. Thanks for the cautious reminder.

[bud37]

Yep, but once cleaned up it will not regenerate as the flammables will have evaporated over time, that is one way to test the sensor, but be careful to fully ventilate after.

[km1125]

QR_BBPOST I found the old cardboard media type fuel filter laying under the engine.

I'm sure when the engines ran and heated that thing up it gave off some fumes. It doesn't take much at all to set the fume sensors off.

The best way to test a sensor is using a small butane lighter. Just place is near (NOT RIGHT AT) the sensor, pull the valve so it releases gas but doesn't light, then with your hand wave those fumes toward the sensor. It will sound right away. The sensors last a LONG, LONG time.

The other thing that I've found that sets the sensor off is old deteriorating soundproofing foam. If I take a block of that and wave it by the sensor, then it will set it off. Sometimes when the engine compartment heats up the same thing happens.

[bud37]

QR_BBPOST Yep, but once cleaned up it will not regenerate as the flammables will have evaporated over time, that is one way to test the sensor, but be careful to fully ventilate after.

Ok, I let the cat out of the bag, my fault ... ....For the record, there is only one correct way to test those sensors and that is with the appropriate test gas for the % LEL the sensor alarms at. It is one thing to make it alarm but really there is no way of telling what the sensor is alarming at. The sensors do have a life span and it will be greatly altered if they are exposed to any high concentrations.......so any of you that have had any of your fume detectors exposed to high concentrations, should look at replacement.....that is the only safe way to consider this. Please be safe , aint nothin to fool with.

[Viper]

I agree with the replacement recommendation. The sensors don't last forever. They can get contaminated with oils, etc. If it's the kind I'm thinking of, replacement sensors are no longer available. Unless you definitely find a source for triggering the alarm, replace it with a newer system (probably should anyway), they're way better than the one you currently have if it's original equipment.

[VicB]

I believe it’s original. This may go on my list of winter projects. Seems like a good idea. Thanks.

[VicB]

Running through old posts and thought if anybody looked at this I would update. Turned out the be the dirty flame arrestors on top of each engine. They were black and gummy. Took them home and cleaned them up and the detector stopped alarming. Additionally, I found a small gas leak on the top screw on the fuel pump of my generator. Removed the screw, fabricated a rubber washer using a set of punches and some rubber. All is well. I really think the flame arrestors were the issue.

[Cooler]

My money would be on that gas leak you found on the genny fuel pump. Does not take much gas to create fumes. Could have been the arrestors. They need to be cleaned occasionally. Once they get bad enough, they turn into flame generators instead of arrestors. I clean mine once a month. Those carbs need air to breath, and oily arrestors prevent that. Way too many people ignore those things. I once cleaned a set from a friends boat that were so bad, it was like peeling lint from the outer side. Really simple job with Dawn detergent and a tooth brush. Good luck the rest of the way! er