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Old 02-08-2013, 07:51   #1
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Need help with diagnosis!

Hello all,

I have a 1983 Yanmar 2GM, and it's been a great engine up until this season.

Now, I'm getting white smoke (that's never happened before) but also the RPMs will drop off suddenly. We'll be motoring along at full throttle (3000 RPMs under load is where it tops out - I've had the boat for 8 years and that's how it's always been) and then it'll drop a few hundred RPMs all of a sudden. Then, it'll come back to full (or maybe it won't). The last time I had it out, it dropped all the way below 2000RPMs and seemed to be having great difficulty - I didn't think I was going to make it back to the slip - but then it finished the day just fine. And yes, I've changed the fuel filters and that doesn't seem to make any difference.

What do you think is going on?

I'd appreciate your thoughts. I know that if I have a mechanic look at it, it'll perform like a champ while he's there and he'll say "I can't find anything wrong with it!"

Thanks,
Chris
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Old 02-08-2013, 07:56   #2
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Re: Need help with diagnosis!

Is it smoke or steam? Could be the injector pump(white smoke while running) or a head gasket(white steam especially at start up). I would do a compression test on it to be sure it is not the latter.

BTW, WOT is not recommended for a diesel. 75-80% is better. Your manual should state this.
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Old 02-08-2013, 07:59   #3
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Re: Need help with diagnosis!

my bet is that it is water in the tank because that matches the lost of rpm that comes back (till the pump can not prime anymore)

But to save typing let me Google this for you: What can cause white smoke from the exhaust
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Old 02-08-2013, 08:14   #4
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Re: Need help with diagnosis!

Quote:
Originally Posted by Don L View Post
my bet is that it is water in the tank because that matches the lost of rpm that comes back (till the pump can not prime anymore)

But to save typing let me Google this for you: What can cause white smoke from the exhaust
+1 water in fuel
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Old 02-08-2013, 10:28   #5
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Re: Need help with diagnosis!

My vote is for water in the fuel, add a water separator, or drain the one you have and see how if runs for a few weeks. I'd also perform a compression test to be sure your head gasket is not blown.
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Old 02-08-2013, 10:35   #6
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Re: Need help with diagnosis!

Yep water in the fuel. Second the add a fuel water separator to your fuel system.
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Old 02-08-2013, 14:03   #7
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Re: Need help with diagnosis!

Just for fun check your oil color at the dip stick and coolant level. If they are fine, it's probably water in the fuel. Could also be a sticking / leaking injector... but that would be more a grey color. White smoke is water.
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Old 02-08-2013, 14:22   #8
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Re: Need help with diagnosis!

I would think that if water in the fuel is making it to the injectors they would be well and truly screwed by now.
White smoke can be a sign of unburned fuel. Steam will dissipate quickly but diesel fog will persist in the air for a longer time.
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Old 02-08-2013, 15:27   #9
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Quote:
Originally Posted by perchance View Post
I would think that if water in the fuel is making it to the injectors they would be well and truly screwed by now.
White smoke can be a sign of unburned fuel. Steam will dissipate quickly but diesel fog will persist in the air for a longer time.
+1

I'd be more willing to point to a fouled injector tip causing an unatomized fuel jet not burning completely. Water in the injectors usually does not end well.
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