Fuel System Check

[K2MSmith]

I keep thinking I am smelling unburned diesel fuel. I was able to find a service manual for the M25 and it shows the various components of the fuel system. I don't see any visible signs of leaks in the engine compartment. Any suggestions I what I should check ? One mistake I remember I made a week ago is killing the engine, but leaving the ignition key "on" for several hours. I hear a periodic "click" sound when it is on. Could it be that maybe by leaving the fuel pump running, there was overflow someplace and that is what I can smell ? The bilge seems pretty clear of fuel and I don't see the fuel gauge going down at all, so if there is a leak it must be small.

 

[Loren Beach]

There should no (zero) diesel leaks, and it sounds like you have a wee small seepage somewhere. Time to follow that fuel line from tank to engine, and then back to the tank.

 

[K2MSmith]

There should no (zero) diesel leaks, and it sounds like you have a wee small seepage somewhere. Time to follow that fuel line from tank to engine, and then back to the tank.

I'm just wondering if it only shows up when the system is pressurized. Would turning on the ignition key without starting pressurize it ? I'm not crazy about going below the cockpit (aka "the coffin") with the engine running....

 

[Frank Langer]

I'm just wondering if it only shows up when the system is pressurized. Would turning on the ignition key without starting pressurize it ? I'm not crazy about going below the cockpit (aka "the coffin") with the engine running....

Lorne is right that careful checking is needed. I would run the fuel pump by turning on the ignition key which does pressurize the fuel system, or just run the engine for 20 minutes at the dock. Then I would take a few tissues and use a clean tissue to gently check every connection - - fuel hose at the tank, in / out at the primary filter, vent and drain at that filter, in / out at the fuel pump, bottom of the pump where many have a screen filter, in / out at the secondary filter, gasket where it screws on, the overflow hoses, the fuel injectors, and finally underneath the fuel tank in case there is a pinhole leak there. I might have missed a check, but you get the idea.
Let us know what you find.
Frank

 

[racushman]

My take would be that if the leak is not obvious... no easy to spot drips, no sheen on the bilge water, I wouldn't worry about it too much. A little bit of diesel goes a long way when it comes to smell. I'm sure leaving the key on (and electric fuel pump pumping) was the likely culprit... which I also have found is easy to do. That said, tracing the fuel line from the tank to the injection pump with your finger will find any spots where something is weeping.

I have spent a lot of time chasing small gremlins with marine diesels. But as long as it runs... and the fuel and fuel filtration is clean, the air intake/filter is clean, and the oil and filter is changed regularly... you should be in good shape.

 

[Christian Williams]

I'd have a look at the tank end. Tanks do develop hidden leaks. Also, old fuel gauge sensors get loose and leak, esp. when tank is filled to top. Some tanks have inspection ports with worn out seals.

If you have a TAFG, it will trap small weepings and they will not show up in the bilge.

As Loren said, there should be no raw diesel smell. But if you fuel from a fuel dock diesel is bright red, which makes evidence collecting quite possible--and also the elimination of worries. .

 

[JSM]

Could it be that what you are smelling is exhaust ? After long periods of motoring I sometimes notice a diesel smell in my cabin. You may want to check the breather hose on your valve cover. On my M25xp the breather hose runs from the valve cover to air filter , occasionally the air filter will shift position allowing the hose to exhaust into the open rather than into the air intake of the engine resulting in a stinky cabin.

 

[markvone]

A side note:

I added a cheap buzzer to supplement the oil pressure light when I rehabbed my engine control panel. It's wired in parallel with the oil light. Because the buzzer sounds when the key is 'ON' and the engine is not running, it provides a warning that the key is 'ON' after stopping the engine. This eliminates running the fuel pump unintentionally and also adding non-running hours on the Hobbs meter.
The downside is that the buzzer sounds every time you turn the key to 'ON' until the engine starts but also to check fuel level or bleed fuel filters.

Mark

 

[mizunoman101]

I'm the guy who notices every smell and hears every sound in the boat... And I notice the very slight smell of diesel in the area of the tank on our E35-3, but I can find no leaks or drips. I think that the fuel fill hose in our 37 year old boat are weeping a bit of smell. I have replaced all the hoses going from the tank to the engine along with a new Racor ... so, who knows. Perhaps it always has a slight odor of diesel.

 

[Loren Beach]

I'm the guy who notices every smell and hears every sound in the boat... And I notice the very slight smell of diesel in the area of the tank on our E35-3, but I can find no leaks or drips. I think that the fuel fill hose in our 37 year old boat are weeping a bit of smell. I have replaced all the hoses going from the tank to the engine along with a new Racor ... so, who knows. Perhaps it always has a slight odor of diesel ago I suspected that the OEM fuel fill hose was permeating. This hose passes down the inside of the hull from the deck fitting, and this is inside the forward hanging locker. The old hose looked fine and had zero evidence of seepage. There was, OTOH, a faint diesel smell in that locker.

About a decade ago I suspected that our fill hose might be permeating - it is routed down the hull inside the forward hanging locker, and there had been a faint diesel odor for a while.
A trick I learned from another boater (might have been from this site, even) was to wet a rag with hot water, wring it out and rub it thoroughly along the outside of the suspected hose. I did, and that rag smelled faintly of.... yup, diesel.
This also works for checking on permeation of the waste hoses, but keep your nose a bit further away.

Anyhow, easy "test" and when you look at the calendar, it's well past time replace that hose anyway. Our mechanic told us that hose technology has improved a lot since the '80's', and the modern hoses have an impermeable inner liner.
Same replacement recommendation, BTW, for the tank vent hose, and the engine supply and return.... when over 25 or 30 years it's time to replace them.
I did all of ours over the course of about a week.
Since replacement, never an odor of diesel.

Best just to think of this as preventative/routine maintenance, and put it in the "25 year column" in your boat work spreadsheet... !

 

[Kenneth K]

I had a persistent diesel smell on my boat. When I pulled up the teak sole (it was already loose) near the engine compartment, it had a strong diesel smell to it. Probably the old remnants of a previous fuel filter change/spill. I think it was the diesel that softened up the sole adhesive and made it so easy to remove.

 

[mizunoman101]

About a decade ago I suspected that our fill hose might be permeating - it is routed down the hull inside the forward hanging locker, and there had been a faint diesel odor for a while.
A trick I learned from another boater (might have been from this site, even) was to wet a rag with hot water, wring it out and rub it thoroughly along the outside of the suspected hose. I did, and that rag smelled faintly of.... yup, diesel.
This also works for checking on permeation of the waste hoses, but keep your nose a bit further away.

Anyhow, easy "test" and when you look at the calendar, it's well past time replace that hose anyway. Our mechanic told us that hose technology has improved a lot since the '80's', and the modern hoses have an impermeable inner liner.
Same replacement recommendation, BTW, for the tank vent hose, and the engine supply and return.... when over 25 or 30 years it's time to replace them.
I did all of ours over the course of about a week.
Since replacement, never an odor of diesel.

Best just to think of this as preventative/routine maintenance, and put it in the "25 year column" in your boat work spreadsheet... !

Excellent... Thank you for the info.