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Old 20-03-2023, 08:50   #1
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3gm30 White Smoke & Max 2000rpm In Forward, Neutral and Reverse Work Normally

Any ideas why this would be happening only in forward gear? Does it indicate a transmission issue? Any other reasons why Neutral and Reverse have full smooth power and forward stops at 2000rpm and starts to smoke white.

I just dove the prop and spun it by hand. The max prop seems to be working fine and freely. I’m probably past due for a cutless bearing change, but doesn’t seem like that could be the issue if reverse works fine.

Any thoughts would be helpful thanks.
Austin
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Old 20-03-2023, 09:04   #2
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Re: 3gm30 White Smoke & Max 2000rpm In Forward, Neutral and Reverse Work Normally

Fixed prop or?

Is the amount of smoke the same when the engine is first started as it as after running it 20 minutes?

White smoke can be engine too cold. too much fuel i.e bad injectors. bad fuel timing. Or warn out rings.
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Old 20-03-2023, 09:59   #3
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Re: 3gm30 White Smoke & Max 2000rpm In Forward, Neutral and Reverse Work Normally

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Fixed prop or?

Is the amount of smoke the same when the engine is first started as it as after running it 20 minutes?

White smoke can be engine too cold. too much fuel i.e bad injectors. bad fuel timing. Or warn out rings.
Max prop 3 blade feathering

The smoke is the same regardless of how long the engine runs. And doesnít explain why it only happens in forward gear. But yes it does behave like too much fuel once it gets up to 2000rpms in forward and wonít go further. But again the key component seems to be reverse and neutral work fine, smooth full power without smoke.
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Old 20-03-2023, 10:13   #4
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Re: 3gm30 White Smoke & Max 2000rpm In Forward, Neutral and Reverse Work Normally

It was fine previously? Or is this a new boat to you?
I ask because it sounds like you are over pitched if it never was right.

If it was fine before, you may have an engine problem, it is doing what my 3GM30 did with a cracked piston skirt. Wouldn't go over about that rpm. But my engine became a bit hard starting eventually also....
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Old 20-03-2023, 10:14   #5
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Re: 3gm30 White Smoke & Max 2000rpm In Forward, Neutral and Reverse Work Normally

Adjust the prop for less pitch. There is a separate adjustment for forward.

You might try servicing the injectors or at least run some LiquiMoly "Diesel Purge" through them. And change the filters. I fill the engine filter with Diesel Purge and let it run at various speeds for 20 minutes.
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Old 20-03-2023, 10:21   #6
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Re: 3gm30 White Smoke & Max 2000rpm In Forward, Neutral and Reverse Work Normally

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It was fine previously? Or is this a new boat to you?
I ask because it sounds like you are over pitched if it never was right.

If it was fine before, you may have an engine problem, it is doing what my 3GM30 did with a cracked piston skirt. Wouldn't go over about that rpm. But my engine became a bit hard starting eventually also....
Been fine for last 12yrs. Definitely a new problem.
Did yours run fine in neutral and reverse?
Also the starting is strong, cranks right up.
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Old 20-03-2023, 10:24   #7
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Re: 3gm30 White Smoke & Max 2000rpm In Forward, Neutral and Reverse Work Normally

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Adjust the prop for less pitch. There is a separate adjustment for forward.

You might try servicing the injectors or at least run some LiquiMoly "Diesel Purge" through them. And change the filters. I fill the engine filter with Diesel Purge and let it run at various speeds for 20 minutes.
The prop has been fine for 12yrs Iím not sure what has changed.

I thought it could be a fuel problem too but doesnít explain why Neutral and Reverse work just fine.
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Old 20-03-2023, 10:41   #8
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Re: 3gm30 White Smoke & Max 2000rpm In Forward, Neutral and Reverse Work Normally

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The prop has been fine for 12yrs Iím not sure what has changed.

I thought it could be a fuel problem too but doesnít explain why Neutral and Reverse work just fine.
The pitch in forward is probably not the same as the one in reverse. Neutral there is no load on the prop. Diesel engine speed is determined by how much fuel you put in them versus what load is on them. In neutral there is no load so you can go up to the governor stop of 3500/3300 RPM or whatever the max rpm limit is on your engine. In reverse there is not as much load as there is in forward so again you have the available energy to reach max RPM. In forward you probably have more pitch than reverse so you need more fuel to meet the load. For some reason you are not making it.

If you haven't done it in a while change the primary and engine fuel filters. Put Diesel Purge in the new filter and run the engine at varying speeds for 20 minutes. If this doesn't improve it either pull the injectors to have them checked for spray pattern and flow. It's possible one of your blades on the prop is not the same as it used to be or the pitch stop may have worn out.
But change filters and clean the injectors just to rule them out.

What was the max RPM you used to be able to get and when did that change to 2000rpm? Was the change gradual or happen all of a sudden?
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Old 20-03-2023, 10:50   #9
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Re: 3gm30 White Smoke & Max 2000rpm In Forward, Neutral and Reverse Work Normally

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Been fine for last 12yrs. Definitely a new problem.
Did yours run fine in neutral and reverse?
Also the starting is strong, cranks right up.
This was years ago. Not sure about reverse, I was long term cruising at the time and seldom used reverse except to anchor. I know it would reverse well enough to set the anchor, but that was probably 1400-1600 rpm or so.

Once started, it seemed to run well and smooth, but lower power and maxed out at 2k rpm or so. I suppose one cylinder wasn't adding much HP due to flow past the piston. It started OK for a month or so, then eventually became hard to start when cold.

I dont remember but reverse likely has a much lower ratio than forward? So easier to reach higher rpm with less load?
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Old 20-03-2023, 14:58   #10
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Re: 3gm30 White Smoke & Max 2000rpm In Forward, Neutral and Reverse Work Normally

Take Scubaseas advice in post #8, it makes complete sense, all of it!
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Old 20-03-2023, 15:09   #11
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Re: 3gm30 White Smoke & Max 2000rpm In Forward, Neutral and Reverse Work Normally

The vee drive and prop shaft are offset about 5* on a Pearson 323 so you can pull the shaft without pulling the engine. It's a left-hand prop. If you had the reverse prop pitch set the same as the front, the prop walk would be so bad you could probably not back up anywhere near straight. I LOVE the propwalk on my 323. I can get on a dock with 30 knot wind blowing off it by heading towards the dock at 5 knots at a 30* angle, put it in reverse and rev it all the way and just like in Captain Rod the starboard 1/4 will pull right into the dock and stop you all in one sexy 3 second maneuver. 323 is a GREAT boat but I lived aboard 6 years and sailed mine a lot.

I would try greasing the Max Prop before adjusting it. It's possible one blade or more is sticking and it's over pitched.
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Old 20-03-2023, 16:06   #12
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Re: 3gm30 White Smoke & Max 2000rpm In Forward, Neutral and Reverse Work Normally

How's the coolant level? White smoke could be steam or burning A/F, head gasket or crack, maybe? Exhaust manifold?
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Old 20-03-2023, 16:46   #13
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Re: 3gm30 White Smoke & Max 2000rpm In Forward, Neutral and Reverse Work Normally

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Originally Posted by Scubaseas View Post


If you haven't done it in a while change the primary and engine fuel filters. Put Diesel Purge in the new filter and run the engine at varying speeds for 20 minutes. If this doesn't improve it either pull the injectors to have them checked for spray pattern and flow. It's possible one of your blades on the prop is not the same as it used to be or the pitch stop may have worn out.
But change filters and clean the injectors just to rule them out.

What was the max RPM you used to be able to get and when did that change to 2000rpm? Was the change gradual or happen all of a sudden?
In the morning I’ll bypass the primary Racor filter and see what happens.
If the prop somehow changed, how would one be able to identify that?

Max was 2500-2600rpm depending on how clean the bottom was. Usually cruised at 2200.

Mechanics came and want to take the head off because one cylinder seems a bit noisy. And they think the transmission is a problem.
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Old 20-03-2023, 16:50   #14
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Re: 3gm30 White Smoke & Max 2000rpm In Forward, Neutral and Reverse Work Normally

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How's the coolant level? White smoke could be steam or burning A/F, head gasket or crack, maybe? Exhaust manifold?
Coolant is fine. I thought it could have been exhaust elbow, so I just put on a new one and it helped a bit but not the problem.

The engine head is coming off tomorrow.
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Old 20-03-2023, 16:57   #15
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Re: 3gm30 White Smoke & Max 2000rpm In Forward, Neutral and Reverse Work Normally

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Ö.. 323 is a GREAT boat but I lived aboard 6 years and sailed mine a lot.

I would try greasing the Max Prop before adjusting it. It's possible one blade or more is sticking and it's over pitched.

I just lubed it last month in Shelter bay marina. It moves smooth like butter.

I donít spend much time on docks so havenít actually gotten used to the prop walk. Perhaps one day Iíll have time to give it a try. And yes 323 is a great boat. Ive had mine for 12yrs now.
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