Diesel smell in H34

B757Captain · Mar 7, 2015

I have always found that diesel exhaust odors don't have a "sharp" smell like raw fuel does. My wife complained of the same thing but I couldn't smell it. The raw fuel smell will permeate clothes, fabrics, etc. If your CO monitor isn't squawking I'd look at the supply side. When looking on my '86 H40 for the diesel smell I eventually zeroed in on a small leak in the fuel tank.

On mine, the cradle that the tank sits on had allowed moisture to collect on one spot on the aluminum tank, causing pitting corrosion an a small hole in the bottom of the tank. The fuel had seeped between the grid liner and hull but years of grit, sand, dirt etc., had absorbed the fuel before it could migrate to the bilge so I didn't have evidence of the leak in the bilge.

Pulled the tank, had it repaired, and in the time the tank was out I dumped about a gallon of degreaser (half a pint or so from a spray bottle at a time) at the spot of the leak. The degreaser ran roughly the same path as the fuel but enough to wash the grit, grime and fuel residue down to the bilge. During this process I finally did smell the diesel and the crap that ran into the bilge was amazing. When it started coming through clean I kept the degreaser treatment going a few more times. Re-installed the tank and diesel smell gone - even according to my wife's hyper-smell capabilities!

Mark

Stu Jackson · Mar 7, 2015

Doug,

Smells, sounds and electrical pictures without wiring diagrams are impossible to help with on the internet.

But Mark makes a good point: it's either a small fuel leak or an exhaust leak.

He also noted the possible culprit of being under the fuel tank, which has been reported many times.

If you have already gone over all the fuel lines and their connections, then the only possibility left is...

While your engine is running, open it up for inspection by taking all the hatches and covers over it off, and start looking around. Two most likely culprits are where the exhaust riser connects to the engine manifold, and where that connects to the muffler.

Also, have you inspected your long exhaust hose from the muffler to the transom recently? We replaced ours after 27 years - it needed it!

You & I have the exact same vintage 34 foot boats.

Good luck.

Capt jgw · Mar 7, 2015

Has to be a leak somewhere, and it only takes just the tiniest bit of diesel to raise an odor. Easiest place to start looking is the hoses from tank to engine. You're looking for any dampness or visible cracking or other deterioration. Rubber hoses don't last forever so if yours are original they're way past replacement time. Next would any fuel related fittings on the engine and filters like the bleed screws. Last and hardest to fix would be the tank itself. Welds can crack and fiberglass can permeate over time. If the tanks are foamed in there's no easy way to check them, but you should get a stronger odor when you open up the area.
If you're not smelling it, maybe you're just not sensitive to the odor, but apparently your wife is, maybe she can help you track it down.

kloudie1 · Mar 7, 2015

had same problem.. After a lot of troubleshooting, found a tiny crack in the diesel return line from the injectors to the tank aft corner. Replaced that and smell is slowly disappearing.. The crack would drool slightly when the engine was running.. Most likely a hose or hose fitting drooling a little making that smell..

Capt jgw · Mar 7, 2015

kloudie1 said:
had same problem.. After a lot of troubleshooting, found a tiny crack in the diesel return line from the injectors to the tank aft corner. Replaced that and smell is slowly disappearing.. The crack would drool slightly when the engine was running.. Most likely a hose or hose fitting drooling a little making that smell..

Leaks in the pressure side can go unnoticed for a long time. Vacuum side are harder to find but the engine will quit so at least you know you have a problem.

Dan Johnson · Mar 7, 2015

YVR...

After checking the hoses, check the bottom of the engine fuel filter for any sign of leakage. The O-ring is very fine in diameter and can leak if not refitted carefully after a change.

Also, one of the bleed screws on the filter is commonly fitted with a plastic washer that can crack and leak if overtightened. The brass washers under the other bleed screws if they've been miss-seated after a loosening and could leak as well.

I use a facial tissue to gently wipe under all hose connections and the filter to look for leakage--diesel will show pink on a white one.

IH82BL8 · Mar 9, 2015

If it's the exhaust side, you should also check the muffler box (maybe the wrong term). In my H31 it's the space under the stbrd cockpit seat. The exh hose from the engine goes into the box, and another hose goes from the box out the stern. If the box isn't sealed, it will leak exhaust into that space. The leak would also put raw water into the space.

Mark48 · Mar 9, 2015

Check the screws on the primer pump to make sure the gasket is working properly. I have been chasing a minor fuel leak for over a year and think it is this gasket. Good luck not an easy task. I ended up removing the starboard panel on the engine cover to get reasonable access. This was not as difficult as it seems.

PGIJon · Mar 9, 2015

just had a leak at the fuel injector pump. Found it using blue colored tissues stuck in all the usual suspected places. Ran the engine for a couple of minutes and the wet blue tissue made it very apparent.