[C320-list] Black smoke with 3GM30F

[Jeff Hare]

The 3gm30 can run for all day at 3000rpm if the exhaust system is clear of buildup. 

That is pretty much the recommended operating point for this engine. At this point, the exhaust and oil temp are optimal and you're running at the best part of the the power curve, so as long the temp is in range don't be afraid of working a diesel at its operating point.

Guaranteed you aren't wearing it out or harming anything. Instead you're keeping the exhaust clean, and burning off the moisture in the oil which helps keep the engine in top form.

We have a similar Yanmar engine in our tractor and it has a green line on the tach at 3000 rpm where it is designed to run whenever you're operating it.

I think the max rpm is around 3800. 85% of that is 3200 and that is a bit high to run for extended periods of time. Ours starts to heat up more at that speed.

Jeff Hare
#809

dprudden <dprudden at comcast.net> wrote:

>Joe,
>Everything I have read on the 3GM30F says to run the engine at around 2900 rpm. That's about 85% of max, which shouldn't be maintained for any length of time. There are plenty of others on this list that know a lot more than I on the engine, but that's what my research has found and a mechanic has verified.
>
>David Prudden
>#787
>
>Sent from my iPhone
>
>> On Aug 17, 2014, at 4:12 PM, JJ Morrison <sail-ability at sympatico.ca> wrote:
>> 
>> Could be your exhaust elbow has carboned up. Exhaust restriction often results in the symptoms you describe.CheersJohnM1999#574
>> 
>>> From: jtamucci at comcast.net
>>> To: c320-list at lists.catalina320.com
>>> Date: Sun, 17 Aug 2014 15:07:01 -0400
>>> Subject: [C320-list] Black smoke with 3GM30F
>>> 
>>> Most of this season, the boat has been sitting on the mooring with not much
>>> sailing or motoring.  In fact I still have the same tank of diesel I put in
>>> last October 2013.  I also have a 3 blade Martec feathering  prop.  At the
>>> beginning of the season, the boat ran great and I could get up to 7 knts at
>>> 3400 RPM and no smoke at all, so the prop pitch seemed perfect.
>>> 
>>> Recently I noticed a fuel leak from the secondary filter so I bought a new O
>>> ring but the leak around the cap continued and when I tried to screw it ona
>>> 3rd time I lost the prime and even after bleeding the secondary could not
>>> get the engine to start.  I had the yard mechanic fix it and they had to
>>> bleed the injectors. 
>>> 
>>> 
>>> 
>>> I went on vacation for a couple weeks and same back. Now the engine starts
>>> fine and will freely rev up to 3600 RPM in neutral.  When I put it in
>>> forward however and give it some throttle, very little response and black
>>> smoke comes out the exhaust.  Max RPM was 2000 with lots of black smoke and
>>> soot.  It works much better in reverse but still some black smoke.  So it's
>>> a classic overload problem due to a fouled prop or drivetrain?
>>> 
>>> 
>>> 
>>> So I dive on the prop but very little fouling but I scrap it clean anyway.
>>> The haul is also clean. Same problem.  So I go down and repitch the prop a
>>> couple times (it has adjustment screw).  The 1st time I repitched, the smoke
>>> went away but I could only get up to 4.9 knts at max RPM of 3100.   After a
>>> couple more adjustments I can get up to 3000 RPM and 6 knts before it starts
>>> smoking at full throttle which gives me 3100 RPM.  The shaft spins easily by
>>> hand turning at the engine, and the prop seems to be feathering fine.  The
>>> engine is not overheating either, and very little vibration in the
>>> drivetrain.  So I was able to improve things but still not like before.
>>> 
>>> 
>>> 
>>> So after all that, my question to you is, is it still an driveshaft overload
>>> problem, or could it be an engine problem?  Could the mechanic have screwed
>>> anything up by bleeding the injectors?
>>> 
>>> 
>>> 
>>> 
>>> 
>>> Joe Tamucci #619
>>