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Old 06-08-2020, 01:22 PM   #1
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Terrible smelly exhaust.. just awful

The boat has two 3208TA 375HP with about 2000hrs. As background, the boat had a mechanical survey in January by a really experienced diesel mechanic. nothing serious (got most of the issues addressed). Normal oil analysis. He never mentioned the smoke being so smelly.. it’s classic diesel exhaust smell but on steroids.

Initially I was not worried about it as I knew that these engines smoke a lot when cold. Finally took the boat out in June.. still the smell is so bad that I could not open the windows on the fly when underway. The smell goes right up to the Fly and Aft cabin. The engines run decent enough.
Had a mechanic from the CAT outfit come out and change all oils, filters, impellers, etc. I did ask him about the smoke and he said all these engines smoke even when new. He said installing a block heater may help in cold months. But it’s warmer now and still lots of smoke & smell.

Any hints or ideas on how to reduce the smell would be much appreciated..smoke I can tolerate, this smell not so much.

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Old 06-08-2020, 01:28 PM   #2
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Go up wind.

Do they reach full operating temperature? Have you run them at cruise for a couple of hours?

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Old 06-08-2020, 01:36 PM   #3
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They normally smoke and stink right after start, and while warming up. But once warmed up and under way, with some load on them, they should burn pretty clean and sorta stink-free. Always will be some stink. It is always worse when sea water temp is low as aftercooler chills the intake air, and worse at low power operation.

What operating conditions give you the problem?

Are both engines doing the same?
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Old 06-08-2020, 02:25 PM   #4
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Station wagon effect?
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Old 06-08-2020, 10:21 PM   #5
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Thank you for the input. I did run the engines for 6 hrs yesterday, they reached operating temp 165-180F. The smoke appeared less when underway, but being underway may camouflage the level of smoke. But the smell remained pretty potent.

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Old 06-08-2020, 10:46 PM   #6
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It is going to be worse when running down wind. Not much to do about that except close up the rear when heading down wind. When heading other directions you may experience the station wagon effect where the exhaust is drawn up and into the boat by the lower air pressure from the boats movement. Unless going down wind, try opening some hatches or windows facing forward to allow air to flow into the boat and break up the lower air pressure area behind the boat. While diesels don’t create a lot of carbon monoxide there is some so breaking the station wagon effect is good to do. My wife will notice the slightest hint of diesel exhaust and let me know about it...
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Old 06-08-2020, 11:10 PM   #7
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Has the thermostat been removed?
Or possibly stuck open?
Too cool running temps can create a smelly situation!
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Old 06-09-2020, 03:23 AM   #8
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Go to underwater exhaust. Quieter, too.
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Old 06-09-2020, 01:53 PM   #9
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The thermostats are still there.. I had my suspicions about the port thermostat as the coolant temp takes a lot longer to get to normal operating levels vs STBD thermostat. I did replace the temp sensor as a first step but it did very little.

Eventually coolant temp reach 165 Port, 180/185 STBD. The smell is still there but I get used to it which is not a good thing.

Valve adjustment at the next maintenance for sure. It will be due.

The underwater exhaust option sounds intriguing, I will dig into it and see if it’s doable and effectiveness.
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Old 06-09-2020, 02:56 PM   #10
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If you have a swim platform above the exhaust outlets it may be contributing to the problem. Try exhaust extensions

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Old 06-09-2020, 02:58 PM   #11
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I've seen some boats with diesels add turnouts to the exhaust to get it out beyond the hull corners so the exhaust gets pulled away by the air coming down the sides of the hull and less gets pulled along behind. I've considered it with my gassers as if the wind is perfectly on the nose or behind us and I don't have the windshield open we occasionally get a few whiffs of fumes and spray pulled up towards the bridge.
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Old 06-09-2020, 03:59 PM   #12
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Originally Posted by rslifkin View Post
I've seen some boats with diesels add turnouts to the exhaust to get it out beyond the hull corners so the exhaust gets pulled away by the air coming down the sides of the hull and less gets pulled along behind. I've considered it with my gassers as if the wind is perfectly on the nose or behind us and I don't have the windshield open we occasionally get a few whiffs of fumes and spray pulled up towards the bridge.
This is what I have. Exhaust is under swim platform around 2 feet from the side. There is a angled fitting with a extension tube with a flap at the end that move the exhaust right on the port aft corner so fumes are moved away when cruising.

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Old 06-09-2020, 06:51 PM   #13
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I love the smell of diesel exhaust in the morning. It smells like boating!
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Old 06-09-2020, 08:24 PM   #14
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Old 06-09-2020, 10:41 PM   #15
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The weather has been a little cold here in the PNW. I have the same engines and they smoke when first fired up. At 2100 rpms they don't smoke much. Your condition is normal for these engines.
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Old 06-09-2020, 11:45 PM   #16
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The thermostats are still there.. I had my suspicions about the port thermostat as the coolant temp takes a lot longer to get to normal operating levels vs STBD thermostat. I did replace the temp sensor as a first step but it did very little.

Eventually coolant temp reach 165 Port, 180/185 STBD. The smell is still there but I get used to it which is not a good thing....
Significant difference. What is correct run temp? 180/185 seems more likely. Does one smell/smoke worse? Are the thermostats identical, ie is there a choice of thermostat? You could check them for model reference. Or test them in hot water of known temp and see if they perform differently.
ASD knows his stuff and his engines but by your description the smell is way excessive.
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Old 06-09-2020, 11:56 PM   #17
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I ran patrol boats used in covert operations. They had the exhaust either go out the stern and turn 90° to exit in the water at about even with the boat bottom. Or after an exhaust loop, went down to the bottom within the engine room. The engine rooms were heavily insulated for sound and idling, engines could not be heard outside the boat. At full speed on a dark night, enemy a couple hundred yards away, had no reaction to the boat passing.

The engines probably have more back pressure, and may burn more fuel to overcome the back pressure. But these were US military boats and fuel economy wasn't something we talked about.
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Old 06-11-2020, 01:16 AM   #18
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Thank you all for the insightful comments. I called CAT today to order a thermostat. I know replacing the T-stat will be a challenge but I was thinking that it would be a good opportunity to cleanout the Heat Exchanger. The parts rep at CAT said there are 2 thermostats (right next to each other) per engine. That took me by surprise, not sure how that would work.

While I was checking things, I found traces of oil in the air filter. Most likely spray from the intake manifold gasket that I know needs replacing. Hoping to do that next week. Will also replace the air filters..

As a side note, I had not pushed the engine beyond 1800rpms for any significant length of time. Usually cruise between 8-12kts.. maybe I should push the engine a bit more next time out for a good 30min or so. Maybe

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Old 06-11-2020, 01:28 AM   #19
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Terrible smelly exhaust.. just awful

Thread header reminds me of someone I know....
Could the oil traces be modest blowby?
2 thermostats? Do they supply coolant to different parts of the engine at different temps?
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Old 06-11-2020, 05:41 AM   #20
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Do those engines have an EGR valve (exhaust gas recirculation). Going back a few years I used to work on a hire fleet of diesel powered light vans Some of them had EGR valves and they used to fail at about 70k miles or so. The initial signs were smoking on start and a really rancid diesel exhaust smell. I used to make a sort of sheet steel gasket to temporarily blank them off.
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