Another Engine Smoke Question

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nveater

Veteran Member
Joined
Nov 4, 2021
Messages
56
Vessel Name
Pathfinder
Vessel Make
Mainship Pilot 30
I have a Cummins 6BT-5.9 210 hp engine (1999) in my Mainship Pilot 30. When my engine goes over 2000-2100 rpm I get white smoke. throttle back and the smoke goes away. Is it steam or smoke ? I don't know while it seems to dissipate quickly, the smoke does appear to have some "body" to it. This is my third year with the boat- the surveyor and later my "mechanic" told me it was steam and not to worry, but I am worrier. The engine does not visibly smoke on start up nor at lower rpms. I have a fairly extensive fuel filter system which I changed this year, replaced the impellor last year- no visible loss of coolant, regular oil changes- engine has just over 2000 hours- WOT engine temp has increased by about 5-7 degrees from last year going from about 184 to 190 (by infra red gun). Engine seems to run smooth- any thoughts about what I should check injectors, turbo, aftercooler raw water cooling system ? As a note the way my boat rides half the external exhaust is under water. Appreciate your comments
 
What rpm can you attain at wot? You may be overpropped.

David
 
First step, I would check all aspects of your raw water cooling- especially intake, impeller and inlet side of heat exchanger(s). Then if no local restrictions found, a raw water system flush with Ridlyme or Barnacle Buster. It sounds like you are not getting sufficient cooling at higher rpm.
 
Steam. Past time but not too late to do some raw water cooling system maintenance.
 
If it hasn't always steamed then it's an indication that something in the exhaust is getting hotter than normal likely due to restricted water flow or uneven water flow through the exhaust mixer.

Some systems are prone to showing steam, especially in cool, damp weather. But an increase in steam or the appearance of it where it hasn't been previously should be investigated.
 
Does it look like this? Steam! 6LPA 2800 RPM, 15 knots
IMG_3214.png
 
Agree that it is likely steam BUT, check the WOT RPMs. You absolutely want to be able to turn the max RPM and at least 50 more.
 
Unburned diesel is either black or dark brown. Steam is white. Oil is bluish white and can be hard to distinguish from steam, and of course it could be both. One difference between steam and oil is how quickly it dissipates, but that takes a lot of experience to distinguish. The easier test is whether you are burning oil.
 
As mentioned above a raw water system flush would not hurt anything and is easily accomplished once you are set up. I keep a five gallon bucket in my tool shed filled with the required bits of hose with adapters, a small Rule bilge pump and a power supply for the pump; although you could power the pump with a set of alligator clips to your boat's battery. It takes me just a few minutes to disconnect the raw water hose coming out of the seawater cooling pump and the raw water inlet hose to the engine's exhaust diffuser. The Rule pump's outlet is directly connected to a flexible hose sized to fit the Rule with a plastic adapter at the other end sized to jamb into the hose you disconnected from the seawater cooling pump. Next, another piece of hose with another plastic adapter to fit the hose you disconnected at the exhaust diffuser is run down to the bucket. Fill the bucket with a few gallons of Rydlime or Barnacle Buster (comes ready to use and as a concentrate) and light off the pump for an hour. You might want to remove the anodes (zincs) in your engine's seawater circuit first. Run the engine when done and all hoses are hooked back up to clear out any residual chemical. I rinse my 315 HP Yanmar after every run with freshwater and conduct a chemical flush as described about every couple of years as well, and I always see the Barnacle Buster solution turn a dirty brown immediately.
 
Hey I appreciate the responses- I now going to explore my cooling system in more depth- I will see how I can set up to do a flush as well. Is this something that should be taken care of ASAP or can it wait till the end of the season ? Thanks
 
You know the old joke, "Hey doc, it hurts when I do this." And the doc says, "Well, don't do that." I would not run the engine in the RPM range where you are seeing the symptoms.
 
After cooler, After cooler. When was it serviced last?

These engines need after cooler service every 2-3 years. Chemicals do not hep the air side of the cooler. Small "o" rigs separate the air and WATER side. Corrosion seeps around the ring and it starts to leak. Chemicals do not help with the corrosion problem either.

These Leaks show up under higher water pressure ( higher rpm) first. Seam is a symptom of a leaky cooler. Creeping up temps are also a sigh of a blocked AIR side of the cooler. As the air side becomes plugged it does not cool the air properly resulting in higher inlet air temp/higher engine temps. Either way start with the AFTERCOOLER.
 
Could not agree more with Greg.
 
So this is the 3rd year I have had the boat and the aftercooler has not been serviced. Now let me ask a dumb question- is the after cooler and heat exchanger the same thing ? When I trace the raw water circuit on my old 6BT there is a pipe from the impellor pump to the oil cooler and then it goes right into the heat exchanger and then into the exhaust- I have tried to look at videos on line but haven't seen my engine configuration.
 
If your old 6BT was a 210 or 220hp model then it wouldn't have had an aftercooler. The aftercooler is not the same as the heat exchanger. The raw water should go to the aftercooler before it goes to the heat exchanger. You'll also see the charge air from the turbo goes through the aftercooler before going to the intake manifold.
 
Based on appearance, this is almost certainly steam. Is the exhaust system overheating? This can occur even if the engine is not overheating. Check the temperature of the wet exhaust, specifically the hose immediately down stream of the mixing elbow. Insufficient water flow, or insufficiently mixed water and exhaust gas, can lead to steam production. Measure temps along the spine or 11-1 o'clock location on the hose at various rpm, and especially at the rpm where you are seeing this. You should not see anything over 165F. This may be a natural feature and nothing to worry about, however, I'd confirm wet exhaust temp to allay those concerns.
More here https://stevedmarineconsulting.com/wp-content/uploads/2014/03/ExhaustSystems170-FINAL.pdf
If you don't already have one, you should have a wet exhaust alarm, more on those here Onboard Alarms – Part I | Steve D'Antonio Marine Consulting
 
I have a Cummins 6BT-5.9 210 hp engine (1999) in my Mainship Pilot 30. When my engine goes over 2000-2100 rpm I get white smoke. throttle back and the smoke goes away. Is it steam or smoke ? I don't know while it seems to dissipate quickly, the smoke does appear to have some "body" to it. This is my third year with the boat- the surveyor and later my "mechanic" told me it was steam and not to worry, but I am worrier. The engine does not visibly smoke on start up nor at lower rpms. I have a fairly extensive fuel filter system which I changed this year, replaced the impellor last year- no visible loss of coolant, regular oil changes- engine has just over 2000 hours- WOT engine temp has increased by about 5-7 degrees from last year going from about 184 to 190 (by infra red gun). Engine seems to run smooth- any thoughts about what I should check injectors, turbo, aftercooler raw water cooling system ? As a note the way my boat rides half the external exhaust is under water. Appreciate your comments
I had the exact same smoke for years until I perfectly checked and clean the raw water inlet and raw water filters (open and clean). I have the exact same engines. I have no more smoke !
 
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