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Old 07-24-2017, 08:41 PM   #1
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Raw Diesel Smell Only While Running the Genset

We have a 2005 Mainship 430 Aft Cabin Trawler. One 8kw Kohler genset and three AC units that are in different compartments from the genset and engine room.

Just recently, when using the genset and the AC units, after more than an hour, the salon has a smell of raw diesel. The forward cabin (separate AC unit) has no raw diesel smell, and the aft cabin (separate AC unit) has a slight raw diesel smell.

When running on shore power and all AC units blowing, no raw diesel smell.

When running the genset with no AC units blowing COLD air, but just air (fan), no raw diesel smell.

When running the genset and the salon AC unit blowing COLD air, there is a raw diesel smell after a while.

While in the engine room with engines on and genset on NO raw diesel smells nothing.

There may a connection between the genset blowing cold air and the genset being on, but Im baffled.

The only maintenance item I recently performed was to replace the genset raw water hose from the seacock to strainer and from the strainer to the genset.

Any ideas?

Jim
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Old 07-24-2017, 09:18 PM   #2
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Where's the tank fill hose routed? Near the returns for the afflicted A/C's? Since you're not picking it up in the ER, look for a source that is common to the return air for those units. A little diesel goes a long way in the air, particularly for those of us with dog noses.
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Old 07-25-2017, 06:07 AM   #3
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Take covers off gennie and look closely for spots wet with fuel. Follow return line to valves and tank and inspect for the same.
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Old 07-31-2017, 09:01 PM   #4
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City: Crockers Boat Yard, New London, CT
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We had an opportunity to trouble shoot this today.

Here are the facts:

When using the generator and the AC, after about an hour, the cabins have a smell of diesel exhaust.

What we have checked:

Changed the both fuel filters today.

Problem: When cruising or stationary with the genset on and the AC on, after a while, there is a smell of diesel exhaust in the cabins.

Analysis:

When cruising with the genset OFF there is no smell of diesel exhaust

When docked, with the AC on and with shore power on – no diesel smell

When docked with the genset on, and NO AC, no diesel exhaust smell.

When docked with genset on and AC on, there is a smell of diesel exhaust.

Looked at all of the genset exhaust hoses from the genset to the muffler and to the thru-hull – no leaks visible. No visible signs of exhaust or water leaks.

While in the engine room where the genset is, no smell of diesel exhaust.

No engine room smoke detectors or CO2 alarms going off.

All three AC units are completely separate from the engine room and sealed off from the engine room.

This occurrence happens docked or moving.

Any ideas?

Jim
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Old 07-31-2017, 09:08 PM   #5
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So is it a smell of diesel fuel or a smell of diesel exhaust gazes?]]

If it is exhaust smell like I understand it, and with genset running and ac running, while at dock or underway, could it be:

1. an ac air intake located nearby the genset exhaust?
2. any open hatch/window nearby the genset exhaust that could received exhaust gazes while the ac is blowing and creating a pressure differential?

If there is no exhaust leak in the boat from the genset (you need to check carefully, can be a leak aspirated by the ac and blow in the boat) it can only be getting some exhaust from outside, either from ac or from blower or window/hatch etc

Or I can be totally off and it is something else

L.
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Old 07-31-2017, 09:13 PM   #6
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After further review, it's a smell of diesel exhaust. I really can't understand it. No smells at all in the area of the generator and the exhaust hoses are intact, but there is a noticeable (gagging) smell in the salon and aft cabin. Can't understand it.

And I have not made any modifications recently.

Jim
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Old 07-31-2017, 09:16 PM   #7
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I suspect that your return air to the AC units is not completely sealed from the mechanical spaces and is pulling some return air from those spaces.
I say this because I had the same problem which I found and sealed with some expanding foam like they use for sealing around windows in new homes.
It became more noticeable as my filters got dirty. Air will find the easiest way into a low pressure area which is your AC space.
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Old 07-31-2017, 09:52 PM   #8
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Quote:
Originally Posted by jimL View Post
After further review, it's a smell of diesel exhaust. I really can't understand it. No smells at all in the area of the generator and the exhaust hoses are intact, but there is a noticeable (gagging) smell in the salon and aft cabin. Can't understand it.

And I have not made any modifications recently.

Jim


This is a long shot, but where is the genset exhaust in relationship to an air intake for the AC? Does the presence or absence of wind make a difference?
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Old 08-01-2017, 09:41 PM   #9
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Thanks all for the suggestions. I am really baffled by this. I understand the basics of HVAC.

There is no outside air intake to any of the AC units. All three use recirculating air. The AC units are in a different compartments which all are located in the various parts of the cabin, separate and “sealed” from the engine room and outdoors.

The AC units, due to the differing air pressures could be pulling air from outside or from the engine room, but there are no odors in the engine room (where the genset is located). I’ll need to check the salon as that is where the odor is most prevalent.

I have new smoke detectors and CO2 detectors all over the boat, in each cabin and the engine room and none have gone off.

The only change I can think of is the addition of a fuel additive, Diesel Kleen, to mitigate smoking Yanmars while idling. The generator is supplied by fuel from the port fuel tank, which was recently treated.

Perhaps, previous to the introduction of diesel kleen, the genset was burning cleanly and we didn’t notice? Once we added diesel kleen, there is a different odor to the exhaust?

I have been in the engine room while the generator is operating and there is no smell. In the salon, it is noticeable. There is no odor in the engine room, or evidence of leaks of exhaust or water.

Jim
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