Diesel Motor Smell

[Rick Johnson]

I know this will not be easy to answer but every time I run the diesel I have a fairly strong smell in the cabin.  Something like the smell of a hot engine but the diesel runs at 160 degrees.  No black water in the bilge.  Aqua-lift muffler does not appear to be leaking.  I have been finding some small amounts of coolant under the motor, but other than that no signs of issues.  Motor starts right up with only a small traces of white smoke.  It just seems like a stronger odor than on my Catalina 30 with the same motor.  I was going to have the oil tested and try to trace the coolant leak. 

I guess my question would be, how strong of a motor "smell" is normal in the cabin after running the diesel?

Cheers,

Rick

[Craig Illman]

Rick - I'm not clear what exactly you're smelling. If it's coolant, go down to the local auto parts store and replace your cap. Even though mine was holding the engine at proper temperature, the outside gasket was letting coolant escape past the cap and not into the overflow tank. It may not solve your issue, but they're cheap. After 18 years, you may be due. I was.

Craig

[Ron Hill]

Rick : Not too sure what you're smelling, but if you are finding coolant under the engine that could be "what's cooking"!! 
To find that leak here's what I'd recommend :  Run the engine until the temp hits 160 and the thermostate opens up.  Then shut down the engine and pull out the steps.  Inspect the engine with a heavy white paper towel.  You should be able to get a visible stain on the towel - up on the engine from the drips that you've found below before.  Look at all of the connections/places where coolant could come out.  Hope this helps.   

[canuck]

I just had a small coolant leak on my M35 which I traced to a loose clamp connection on the port rear side of the engine. I also retightened every possible clamp in the system. I had a mechanic run a 15 PSI pressure test for 15 minutes with no pressure loss. Little leaks become big leaks at the most inopportune times. I also replaced the coolant which was 4 years old.

[Ken Heyman]

 Rick,

We just completed our 6th season with our 34 and I must confess we still have some odor in the cabin when running the engine (and afterward). Certainly check your coolant issue. If I can believe my gauges our engine has always operated within normal ranges----so why our odor? I am pretty convinced at this point that it is simply the smell of a combustible process with heat occurring in a small space. Arguably all odors and gases should be vented up and out but still it is an engine. I have noticed the same odor on other boats but generally we don't spend allot of time "down below" while steaming. I even bought a monoxide detector (a cheap one) and placed it strategically around the boat and engine compartment while running and all was well.

Venting is very important. If conditions permit we always keep a couple of ports and a hatch cracked while underway. I think this has helped significantly. Nevertheless at the end of season, when we bring our cushions home, it is clear that they have been on a boat with an engine.

Maybe there is something amiss but at this point I doubt it.

Good luck troubleshooting.

Ken

[Bob K]

Rick,
We had a diesel smell on our C27 when running the engine.  The problem was the diesel crankcase vent hose - it needed to be routed such that it's open end was close to the air intake, so any vapors exiting the hose get sucked back into the engine.  Once I figured that out, the smell was gone.  We don't have that issue on our current boat, and the vent hose is not all that close to the air intake.  Hope this helps....

[jwwarwick]

I also had the same smell and it was coming from the crankcase vent hose which normally runs down below the engine and stops. The fumes were causing the smell. There is a modification described in the Tech Notes which requires extending the vent hose up to the to the air intake for the engine. I drilled a hole in the intake nozzle on the air filter and used a plastic wire tie to secure the end of the hose so any fumes would be sucked into the intake for the engine. This is just before the air filter. It is my understanding that later models have this modification built in to the engine where this line is tapped into the intake manifold and after the air filter. My boat is a 1989 model and this solved the problem for me.
John Warwick
September Morn in Virginia Beach,VA

[mainesail]

It sounds like a crank case ventilation issue. this is what I did to solve that issue:

I found a K&N filter at a motorcycle shop with the same diameter as the intake throat on the M-25. Sorry I can't remember the part number but I do think it is a K&N RU-2450. The arrow is pointing the the 90 degree brass fitting I inserted for the PVC valve I made.


Here's a picture of the PCV set up I made. The hose runs from the valve cover to a brass nipple with hose barb fittings threaded onto each end of it. Inside this brass nipple I rolled up some oil absorbing pad, loosely, so as not to restrict air flow, to absorb any stray oil escaping the valve cover so it would not pass back into the intake. I would change this at each oil change.

By adding this PCV valve I no longer had any oil smell in my engine compartment after running the engine. The factory set up just vents the crank case into the engine compartment! If you add a K&N make sure you have enough room in the underside of the filter for the 90 degree fitting for the PCV hose. My K&N was off set slightly giving me room to drill through the bottom and insert the 90 degree barbed fitting. I purchased all the brass fittings at Home Depot and did the whole project for under $50.00.

[Mike and Joanne Stimmler]

Mainesail, great info and great pictures. One more project to add to my list.

Mike

[Ron Hill]

Ricks' smell could be that vented oily air from the oil breather.

Back in the mid 1990's I did put Westerbeke's solution of placing that oil pan vent hose end in front of the air cleaner in the Mainsheet tech notes.  However, I couldn't get myself to vent that hose into the air intake.

When I first got my 1988, I knew that the oil pan vent (over time) would make a oily engine and attract dirt.  So I devised a filter that the oil pan air had to go thru and wrote it up in the early Mainsheet tech notes.
Changing that filter 2/3 times a year, it's amazing how much oil that filter catches.  Unlike a gasoline engine (gasoline is a great solvent!) I'm still not too sure today if I'd recommend putting all of that VERY oily air in to the intake manifold of a diesel!! There's nothing to clean that airway.

I still use my "beer can bottom" and foam "cylinder" inside a round eve leaf drain, to catch that air suspended oil and clean it 3 times a year.  A thought   

[Rick Johnson]

Thank you all for the suggestions.  The odor has always seemed to be some type of hot oil smell.  I'm not sure what coolant would smell like and I'm still trying to find my leak (Starboard side towards the stern, if anyone has a suggestion), but it's so slight I don't think that's the source.  The crankcase ventilation seems to be the likely cause.  I'm going to give the filter idea a try and see what happens.

Cheers,

Rick

[Tony Benoit]

I am intrigued by Mainesail's homemade PCV setup pictured in this thread.  Has anyone else done something like this?  I am worried about very fine particles from the crankcase getting into the manifold.  Could they clog the injectors?  Or am I misunderstanding how diesel's work?

I took the air filter off my Universal 23XP and it looks like it could take a hose fitting although the metal is very thin.  I think I would have to support the hose very well.  Is the K & N filter sturdier?

I've been getting an oil smell, especially later in the season.  I assume it gets worse because the oil in the crankcase gets older.

Thanks,

Tony
Helen C #903

[Ron Hill]

Tony : Don't worry about oil particales clogging the injectors. 
I worry about the amount of oil that I capture in my home made filter collecting and clogging the intake manifold.   See my post above. 

[Tony Benoit]

Thanks for the suggestion, Ron.

I like the idea of running the crankcase off-gas into the engine to burn it.  But perhaps I will try to rig a filter of the sort the Ron recommends.  Some sort of hookah without water in it should work fine ;>)

[David Sanner]

I was checking out the beta marine Kubota packaging recently. They have the crankcase
vent  directly plumbed into the intake manifold.  They didn't seem concerned about a
little bit of oily smoke in the manifold.

They also have some nice updates: heat exchanger on top of the water jacket manifold
with the raw water being injected into the exhaust right at the motor, mechanical
fuel pump, electric fuel cutoff, easy access to fuel filter, cast aluminum oil pan
with the pump out connected to the back of the pan.

They had a paper air intake filter inside a well sound insulating cover.
It was impressively quiet when running.