Strange noise from my port fuel tank today

matt_unique

As a matter or prudence I always take a look into my rear bilge ports to see if there is water in the sponsons. Today with my engines running I looked into the port door and heard a strange noise.

I localized it to my port fuel tank when the engine is running. It initially sounded like arcing electricity. Obviously if that were happening in the fuel tank it would have already blown up. I looked in every port sponson orifice available on the Tomcat, front and back, and could see around the tank. There were no flashing lights, no smells, nothing like that. The more I thought about it....it could also be the sound of a partially plugged fuel line intake. The sound is loudest if I open the port fuel tank cap and lay my ear on it. The sound was intermittent but definitely when the engine was running.

Now...I also noticed a somewhat similar sound on the engine itself when I first turn the key on. I was thinking this may support my idea about a partially plugged fuel intake because I'm assuming my engines essentially draw in fuel via a fuel pump when you turn the key. The sound could be that of some air or something....not sure so I welcome any suggestions on the noise.

I ran both engines today from idle to 4000 rpm with no problems, no hesitation on the port engine, etc. I'm very low on fuel but certainly not empty.

Thanks for the ideas.

tsturm · Posted: Sun Oct 12, 2008 9:09 pm Post subject:

over flow check ball in the vent line??
what did it taste like?? Laughing

thataway · Posted: Sun Oct 12, 2008 10:01 pm Post subject:

The Tom Cats have anti siphon valves---not sure if this is the noise. The valve is at the top of the fuel pickup.

matt_unique · Posted: Mon Oct 13, 2008 8:06 am Post subject: Noise

Captains Cat · Posted: Mon Oct 13, 2008 8:48 am Post subject:

I haven't tried but how do you got to that part of the tank top? Is there an access? My gauges are so far off, I've thought about replacement or at least recalibration...

Charlie

YACD · Posted: Mon Oct 13, 2008 11:20 am Post subject:

This is just a wild guess but could it be something outside the tank vibrating and hitting the tank randomly, like the straps or buckles holding it in place. If the tank was nearly empty that might sound louder when you put your ear to the filler. Also, could the the fuel level device inside the tank be implicated? Neither of these would account for the noise at the engine though.

thataway · Posted: Mon Oct 13, 2008 6:33 pm Post subject:

Charlie, on my boat you can access the fuel guage on the port side tank though an access hatch in the floor under the dinette area. The Stb is not readily accessiably. As far as the pick up fittings they are semi accessiable thru the round cockpit side wall hatches. Fortunately my guages seem to work well, plus I have the flow guages, which have been spot on.

matt_unique · Posted: Sat Jan 24, 2009 2:10 pm Post subject: Fuel pickup tubes

Well today I have been working on removing the port side fuel pickup and antisiphon valve. What a nut buster of a job...in part due to the limited access and the fact that you can't get any leverage.

A few lessons learned at least for me:

1.) Unless you can get some kind of leverage with a screw driver head at the base of the fuel lines you cannot get them off without cutting at least a portion of the tip of the hose.

2.) The metal fuel (and fuel vent) knobs are shaped such that the hoses go on easy and come off very hard. (Much like a fishing hook goes in easy and comes out hard).

3.) The *only* way I could get the fuel pickup tube out was to first use heat to break the seal around the antisiphon knob, then using a wrench remove the antisiphon valve from the fuel pickup tube, then remove the fuel vent hose from the tank (was able to use a screwdriver leveraged against another wrench laying flat on the tank), then using an adjustable wrench remove the fuel pickup tube, and lastly, cut the end of the hose on the antisiphon valve and with pliers open up the end and pull like hell. If you had the assembly in your hard this would hopefully make more sense.

The replacement fuel pickup tube sent to me by C-Dory was 2/8" shorter than the fuel pickup tube that came out. Probably small potatoes but I don't like the idea of giving up even 2/8" of fuel considering the length of the fuel tanks. The screen at the end of the fuel pickup tube was perfectly clean and I could blow air through it easily.

Any reason I should not use the existing tube and just replace the antisiphon valve? I could not see anything wrong with the antisiphon valve either but while I'm there I may as well replace it.

Larry H · Posted: Sat Jan 24, 2009 2:46 pm Post subject:

Matt,

Was the sound like a metallic rattling or the sound of sucking on a straw when a milk shake is near empty?

If so, that could be the anti-siphon valve. The valve has a metal ball held against the seat by a spring. There must be a certain amount of vacuum in the fuel line to open the valve. When the fuel pump sucks, the ball rattles against the seat. Depending on the type of fuel pump, the action can be intermittent. This is normal operation and sound. Further, when the tank is near empty, and is made of aluminum, the tank amplifies the sound.

matt_unique · Posted: Sat Jan 24, 2009 5:17 pm Post subject: Sound

Hi Larry,
I mentioned this in my first post but the best way to describe the sound was arcing electricity. It's definitely not a normal sound. It was very noticeable and only cropped up at the end of the season. It's loudest when I put me ear on the open port fuel cap.

thataway · Posted: Sat Jan 24, 2009 5:45 pm Post subject:

I had to replace the anti siphon valve (port tank) due to restriction of fuel to the engine. I didn't remove the pickup tube, just unscrewed the anti siphon valve, and replaced it. In my boat there was at least 4 feet of extra fuel hose, and I removed all but a foot extra. That way, there is still plenty of fuel line to allow cutting of the hose off the fuel barb (aptly called because as matt found out, it is difficult to pull off).

matt_unique · Posted: Sat Jan 24, 2009 6:01 pm Post subject: Fuel tank

matt_unique · Posted: Sun Jan 25, 2009 12:11 pm Post subject: A few more tips

OK I've completed the project and learned a few more tips in the process:

1.) The very first step is to remove the inset line cubby. This will provide light AND much greater access to the hoses, fuel sending unit, ground wire, etc. This also allows much better leverage for wrenches.

2.) Forget the screwdriver on the hose clamps, on the Tomcat I (finally) used an 8mm socket. This will make the clamp removal faster and easier.

3.) The best tool for removing the fuel pickup hose assembly (after removing the antisiphon valve barb) is a crescent wrench. The head of this assembly is shaped like a rectangle and the crescent wrench makes this job much easier.

4.) When removing/reinserting the fuel pickup tube assembly, be careful when you get to the tip. The plastic fuel hose has a wire mesh filter at the end. It just *barely* fits into/out of the hole to the tank but take your time and wiggle it without too much force and it will get through.

5.) The most versatile compound in scuba diving is spit, and this also works well to lubricate the valve barb for the fuel pickup and fuel fill hose barb. Slather some spit onto the barbs and the hoses will slide on much easier.

6.) I will double check but I think the antisiphon valve barb takes a 9/16 wrench......

Phew....done...hopefully the new antisiphon valve will address the noise I heard at the end of last season. It was also good for me to remove the fuel pickup hose to inspect the filter.

Doryman · Posted: Sun Jan 25, 2009 1:58 pm Post subject: Re: A few more tips

thataway · Posted: Sun Jan 25, 2009 4:20 pm Post subject:

Matt,
My antisiphon valve had a restriction in it--had to do with the ball moving and clearing its seat. I carry an extra one in "case"--one could just use a hose barb, but the ASV is safer.