3126 smoke

D

DagoBy

New Member
Sep 20, 2010
22
Osage Beach, MO
Boat Info
1996 450 Sundancer
Engines
3126 CAT
I have a pair of 1996 3126 CATS. One was replaced as mentioned in earlier post due to broken valve. The other is over the 600 hour mark and runs great. I have been noticing a smokey gray haze behind our boat. Not burning any oil and filters were replaced at the beginning of the season. Any suggestions?
 
when do you see the smoke? what RPM's are you running and what is your gps speed when you see the smoke. What's your WOT RPM?
 
I am running at 2300-2400 RPM which shows 19.6 knots. I see the smoke at about any speed. The lower the speed the thicker the smoke. My WOT is around 2800-2900 I think. I am still using the original analog tachs which are a little "jerky"
 
Do you know if one or both of the engines are smoking? Do they smoke at idle?

On my boat, at 2300 rpms I'm doing about 20kts. at 2400 i'm around 22kts. so it seems you're a little slow. Have you checked the bottom and running gear for growth or slime?

I'm by no means able to diagnose your problem, I'm just asking questions that I would ask myself to try and narrow down exactly what is going on.
 
It does smoke from both engines at start up and until it warms up. The new engine smokes a little less, but I figured this would be normal since it is new. The speed and tach readings that I am giving are from the original electronics on the boat, so I don't have a whole lot of faith in their accuracy. It appears that the smoke is coming from both engines, but it is hard to tell at cruising speed. I am in fresh water and the bottom paint is 2 years old, so I think the bottom and the running gear should be fine...but I have not pulled it to see. I appreciate your thoughts and hope you have more
 
The dark smoke is unburnt diesel. blue smoke is oil. So if you're seeing dark smoke at cruise, and you're running slow (you need to verify speed and rpms) then my first guess would be that you're overloading the engines. If you don't know the condition of the bottom, that would be the first thing I would check.
 
Mike, I'm with you regarding the bottom creating a drag and overloading the engines. However, the conflicting piece of information is that the smoke is there at any speed. I definitely agree if it was just a cruising speed, but I don't think that DagoBy overloads the engines at slow speed. Is it possibly a fuel related issue?
 
Your new engine: Was that a Cat Remanufactured complete, Long Block, Short Block or an engine from some other guy?

In your other post: you mentioned the old engine smoked some. Is this smoke you’ve always had or something recent with the new engine deal?

Are you looking to get your hands dirty or wondering about calling in a Tech?
 
If the engines are overloaded, they'll be at all speeds. If I advance my throttles too fast, right where the turbos start to spool up, i'll get a puff of smoke before the turbos catch up. If both engines are smoking, then it's most likely something they have in common. That's the hull and fuel (that's all I can think of). it's real easy to check the hull, not sure how you check the fuel.
 
I was thinking as far as overloaded: If the engines can make rated rpms, then there not overloaded. But He's kinda giving us a Brett Favre on the WOT rpms... "I don't know, maybe"
 
Actually, now that Ron mentions it. did they bolt on all the old stuff from the other engine like aftercooler and turbo?
 
Sorry for the "Farve" response, but its the best I can do....I need new tachs. The new engine was a short block installed by the cat dealer. New turbo same after cooler. Boat has always smoked. Would love to find the problem myself!!
 
Do you run your boat with Tabs down? if so, how much down? I run mine with pretty much full tabs at 2200-2300 rpms. I'll lift them up a little around 2400.

also, if you pull out your panel with the tachs, on the back of the tachs is a rotating selector switch. note where it's at and exercise it back and forth. This should get rid of your jumpy tach syndrome.
 
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Tabs at 3/4 to full depending on the load. There is soot on the transom, but not bad. The smoke that I see at cruising speed just seems to be a light "haze" behind the boat that you have to look at hard to see it. at start up the smoke is heavier and just disipates on its own. I also notice fuel on the water around the boat at start up....not a lot, but noticeable.
 
Turtlesboat said:
If the engines are overloaded, they'll be at all speeds. If I advance my throttles too fast, right where the turbos start to spool up, i'll get a puff of smoke before the turbos catch up. If both engines are smoking, then it's most likely something they have in common. That's the hull and fuel (that's all I can think of). it's real easy to check the hull, not sure how you check the fuel.
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Mike,

In this scenario it sure makes sense, b/c you're describing excelleration. I was thinking about running at different speed continuesly. I could be wrong, but if for example you're trolling, is it possible to overload the engines? I wouldn't think so.
 
put 300lbs on your back... walk real slow, or real fast. you're still overloaded regardless of speed. If you're overloading an engine, it doesn't mater how fast you are going, the exertion is more than it's supposed to be at any speed. maybe a better example is riding a bike. you can gear a bike depending on weight and terrain. if I gear it too high, it's really a hard ride no matter where I go ( maybe a little easier if i'm not climbing hills). If I gear it just right, I can ride all day long and still have a little reserve for a backpack or a hill here and there.
 
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Turtlesboat said:
....maybe a better example is riding a bike. you can gear a bike depending on weight and terrain. if I gear it too high, it's really a hard ride no matter where I go ( maybe a little easier if i'm not climbing hills). If I gear it just right, I can ride all day long and still have a little reserve for a backpack or a hill here and there.
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Mike,

I like your riding a bike example. It makes perfect sense to me.

So, I would think that if we go with the theory that the engines are overloaded the OP has to see the same smoke but with different proportion at different speed, where less smoke at trolling speed and more smoke at cruising and most at WOT speeds.

I have the following specs info on the CATs. It's from 400DB, so we can ingnore most of the readings but WOT rating should still apply:

CATs_Specs.jpg


So, as I recall OP stated that he reaches 2800-2900RPMs and the specs state WOT 2800RPMs. I would think that he's running within the specs and the engine shouldn't be oveloaded. However, the WOT speed is what can help us here. If the boat lost the rated WOT speed, then it's most likelly the bottom drag that's causing the issue making the engines work harder, hense proving Mike's theory.
 
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