# Yanmar 3GM30F



## Bill Mc (Apr 10, 2006)

Friday night we arrived at the boat and stowed our gear. The better half and I were discussing leaving the next day in the morning and not like our last adventure when I quaffed 151 Rum into the wee hours and we wound up spending the weekend in the slip, I thought is was a damn good weekend, go figure, but I digress. To end the Discussion we immediatly cast off the dock lines and began motoring to one of our favorite little harbors (Bath) to spend the night on the hook as we motored along at 2250 rpm it was getting dark so I kicked the rpm up to 3100 after about 45 min the overheat alarm rang out so we secured the engine and set sail. after tacking for about 1 1/2 hrs just to let the engine cool we dropped sail and made our way into Bath creek and made fast to the hook. I forgot to mention our nav lights failed to work, whew. So the question to this long winded explanation is why would I overheat and what would the max rpm be for this engine? I hear that 100% is OK, others state 70-80% of max rpm. Then I get all the what if explanations. ie prop pitch, STOCK, plastic bag/ dirty strainer, NOT strainer was clean. So I am totally open to some more suggestions short of a complete overhaul..

Fair Winds,

Bill


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## Melrna (Apr 6, 2004)

I would check a few things. First, your water impeller to see if it is missing any blades or blades damage. Second your heat exchanger. It could be blocked. Zinc anodes are usually the culprit. From there I would check your exhaust elbow. I know on some boats the exhaust elbow is too small and the next size up eliminates the overheating at higher RPM. Another cause can be barnacle build up in the intake, restricting flow. It is just a start but I am sure the mechanics here will chime in. Now back to my pink jobs! Cinnamon rolls coming up guys!


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## JohnRPollard (Mar 26, 2007)

Melrna hit all the obvious points, pink jobs notwithstanding.

The only other thing I'd mention is that 3100 rpm sounds a bit high for that engine for continuous operation. I know it's within the rated rpms, but subject to all the caveats relating to prop pitch and size, we have the same unit in our boat and we cruise in the 2700-2800 range. We occassionally will do brief bursts into the low 3000s during docking manoeuvres, etc, but the engine just sounds like it's really working hard at those rpms so we don't stay there long. Maybe consider running at lower cruise rpms, i.e. < 3000.

Now about those cinnamon rolls....


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## jrd22 (Nov 14, 2000)

I would agree with John(above) that 3100 is too high for continuous operation. Max RPM is 3600, we cruise at 22-2500, anything above that and we start to see more smoke/steam out the exhaust. If you run it again at normal RPM and don't have an overheat alarm come on you probably don't have any problems.


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## camaraderie (May 22, 2002)

3100 rpms on a yanmar designed for 3600 rpm is WELL within limits and should be able to be run indefinitely at this speed. I had a 4JH with 80-90% of rpm limit and ran for years with NO problem whatsoever. MackBoring will tell you that running at 80-90% is ideal & they should know. Of course it is possible that the boat is over propped but if you are not seeing smoke normally at this speed then I would say to check the things Melrna mentioned before I throttled back permanently.


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## NOLAsailing (Sep 10, 2006)

I would also like to chime in and say that a motor rated at 3600 Max RPM should have no problem at 3100. Normal cruising RPM should be around 2900; 2250 is under-reving the motor.

In addition to the other thoughts - you may want to check your hoses. As they age, the suction created by the higher pressure at higher RPM's can cause them to restrict flow. If the hoses are older, replace them as part of normal maintenance and you may see an immediate improvement.


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## Bill Mc (Apr 10, 2006)

*Still scratch'n me noggin..*

Prop is original size and pitch and clean, no barnacles.
Fresh water cooled engine, so no internal zincs.
Impeller is fresh, Just replaced by yours truley so I know at least this is right.
Only smokes a little when started after a week long layup, this has been improving since the marina in their infinite wisdom used  EITHER  to get her cranked to do my bottom job. { I will no longer beat that dead horse}.
I believe we were doing about 6 kts at 3100 rpm and 5.3 kts at 2250 rpm.
70% = 2520 rpm, 80% = 2880 rpm, 86% = 3100  3100 = BAD???

So I'm still scratching my head on this one. Thank ya'll for the feedback. I'll get this figgered out if it kills me. Financially that is...

Fair Winds,

Bill


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## Rockter (Sep 11, 2006)

If it's an older, raw cooled motor, scaling can be a problem, as for my olde Volvo MD17C.
Sometimes, whan scaled, the poor motor has trouble getting the coolant to reach those regions that would be cooled easily when new.
Though I have never used them, some owners recommend the use of de-scalants. make sure the motor is hot before you circulate them, or the thermostat will not let them into the motor coolant jacket.
The last rtesort is to take off the exhaust manifold and de-scale all that you can see.
In my humble opinion, I would not run an older motor that hard... 3100 rpm is pushing it a bit... that's 86% of max.


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## Vasco (Sep 24, 2006)

Bill,

I would check the impeller. I know you said you recently replaced it and that may be the problem. It may have been an old dry one or got squished a bit going in and now has lost a vane. On the 3GM30 they're pretty easy to get at, unless you have a C&C where it's real hard to get at that side of the engine.


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## sailvi767 (Aug 25, 2007)

If your max RPM is 3600 on that engine it is important that the engine is able to run at a minimum of 90% of rated RPM. If it won't then Yanmar will deny all warranty claims as the boat is overpropped. The newer yanmars run at a lower RPM. I actually thought your max is 3800. The engine should be able to run forever at 90% of rated power. Running a diesel long term at lower RPM's (under about 80%) leads to wet stacking which is very harmful to the engine.


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## Jeff_H (Feb 26, 2000)

I have the same engine. If remember correctly in the manual on the 3GM30F the recommended continuous operation is 2800 RPM and that is the RPM that I run my engine.


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## rperret (Apr 11, 2003)

might have missed this - but did you test the Thermostat?

Rick

quote=Bill Mc;198391]Prop is original size and pitch and clean, no barnacles.
Fresh water cooled engine, so no internal zincs.
Impeller is fresh, Just replaced by yours truley so I know at least this is right.
Only smokes a little when started after a week long layup, this has been improving since the marina in their infinite wisdom used  EITHER  to get her cranked to do my bottom job. { I will no longer beat that dead horse}.
I believe we were doing about 6 kts at 3100 rpm and 5.3 kts at 2250 rpm.
70% = 2520 rpm, 80% = 2880 rpm, 86% = 3100  3100 = BAD???

So I'm still scratching my head on this one. Thank ya'll for the feedback. I'll get this figgered out if it kills me. Financially that is...

Fair Winds,

Bill[/quote]


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## Melrna (Apr 6, 2004)

sailvi767 said:


> . Running a diesel long term at lower RPM's (under about 80%) leads to wet stacking which is very harmful to the engine.


Can I ask a stupid question? What is wet stacking?


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## camaraderie (May 22, 2002)

A diesel engine is subject to "wet stacking" or over fueling if run for long periods of time with ultra light loads (less than 40% of the rated output). "Wet Stacking" causes the engine to smoke and run rough because the injectors become carbonized. Running a heavy load will usually clean up the over-fuel condition and allow the engine to perform properly. Diesel engines operate better and more fuel efficient when loaded (70-80% of the rated output is optimum). Source: http://www.allworlddieselgen.com/faq.htm

This condition happens to a lot of cruising boats who rely on running their main engine to charge their house battery bank while at anchor. I would also note that other experts say this can happen at higher loads than 40% and that cruising at 80-90% of rated RPM's is best. Main thing is to cruise at least at 70% RPM's and don't run your engine while atanchor to charge batteries!


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## JohnRPollard (Mar 26, 2007)

Our 3GM30F is rated as follows:

- 27hp @ 3600 rpm for one hour
- 24hp @ 3400 rpm continuous

I have always assumed the recommendation to run at 80% rated power was referring to the continuous rating, yielding 2720 rpm. We run ours between 2700-2800.


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## sailing320 (Jul 5, 2007)

Somebody please help me on this but I believe the problem could be that the shaft is to tight and needs to be loosend. The water needs to be dripping a certain rate every minute. The same problem has occured on my Island Packet with the same engine.


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## Rockter (Sep 11, 2006)

If the shaft gland were over-tight, and causing a drag on the shaft, it would absolutely fry. The heat build-up would be overwhelming and would risk twisting off the stuffing box assy.

I don't think it is that!


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## Jeff_H (Feb 26, 2000)

The answer is simple, back off the packing gland nut a small amount. There typically is a locking nut and the packing gland nut, and a nut shaped casting on the end of the packing gland itself. You need to be able to hold the packing gland nut with one wrench to keep from twisting the packing gland while loosening the locknut with another wrench. Then you need to hold the nut shaped casting with one wrench while loosening the packing gland nut with a second wrench. I would loosen the packing gland nut roughly an eighth turn, and lock down the locknut again. The packing gland should not leak when the engine if off. There are various opinions on how much water should leak out when the shaft is turning and some of that is dependent on material used for packing. I haven't had a packing gland on one of my boats for over 25 years but if I remember correctly they used to say, 1 drip per minute. 

Jeff


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## TSOJOURNER (Dec 16, 1999)

*151 Fix*

Just apply generous amounts of 151 Rum until the problem ino longer becomes a concern.

Warning!! This is only a temporary solution and may require multiple applications.


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## Rockter (Sep 11, 2006)

Even if the drag on the shaft was the equivalent of 1 hp, the local heating would be about 700 Watts and it would steam, and steam and steam.

If in doubt, slack off the packing and see if it improves. Whatever you do, do not over-tighten it. Let it drip a little. It does no harm.


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## jrd22 (Nov 14, 2000)

Bill- I was just re-reading your post where you said that at 2250R's you were making 5.3K and at 3100 you were making 6.0K. For that large an increase in your RPM's you didn't gain much speed. This would indicate to me that you were trying to push the boat past it's hull speed which would definitely be working the engine hard(heat), regardless of what manufacturers recommendations are. Most likely you are overpropped a bit IMHO. 
In my earlier reply I should have mentioned that I have an Autoprop, this automatically and continuously adjusts the pitch on the blades based on engine RPM and boat speed. We get the most bang (speed) for our buck (RPM) at between 22-2500 RPM and the engine is not working too hard but is still loaded up well. We can run it all the way up to 36-3700 for short periods, or run it continuously at 30-3200 but the increase in boat speed doesn't warrant it. 15 years on the engine, couple thousand hours and it's running just like when it was new (I hope saying that doesn't jinx it ) John


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## TSOJOURNER (Dec 16, 1999)

*Another 3GM30F Question*

I, too, have a 3GM30F - a 1992 that was rebuilt in 2005. I bought the boat this summer and there was zero hours on the engine since rebuild. She starts every time and runs well but I did not realize you shouldn't run the engine at low RPMs.. most of the time I am in no rush to get off the water (as you can imagine) so I will hand the tiller to a friend, and put the rpms around 1500 while I go about getting sails down and covers on.. I kind of enjoy a nice slow putter..

However, it sounds like I should not do this? It isn't used too much - maybe an hour or two a week, tops. I know that when I get up towards the 3k RPM range I get pronounced smoking (white) out the exhaust but I have never left it that high long enough to see if it clears up when the engine warms up.. likely this is just moisture/steam, or suggestion of more troubling problems?

Thanks in advance, sorry to hijack the thread.


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## JohnRPollard (Mar 26, 2007)

Bitcoal,

I think you're okay -- you've only had the boat for a short while and can't have put many hours on that rebuilt engine yet. As a matter of fact, depending on how complete the re-build was, you're probably supposed to break it in a bit at lower revs. 

But in the future rather than puttering along at 1500, go ahead and push the engine harder when you're using it. Something in the 2600-3100 range is probably about right for this engine. As far as I know, ALL the mechanics/experts agree this is better for the engine in the long run. You'll also get better charging from the alternator to your batteries. 

Our philosophy is that if we have to motor, we may as well do it at flank speed -- get there sooner with a better charge to the batteries. But upon arrival, we do throttle back and cool the engine down for a few minutes before killing it completely. Usually the time it takes to drop anchor or secure the mooring pennant is about right.


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## Bill Mc (Apr 10, 2006)

I have the PSS shaft seal, so no bind there. I will however replace the thermistat. I think that this is a great idea, low cost and so obviosly overlooked  I will keep ya'll posted. But, do to work I'll not get out to the boat for a while.


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## hazmat17 (Sep 27, 2007)

My first post here - wonderful site! Have the same engine in my parent's 1992 Freedom 38 (since dad payed for engineering school, I've been designated "chief mechanic")

Lots of good suggestions so far, especially about underloading the engine. These little beasties are made to run & run hard. I've got a small diesel tractor that I often run at max rpm - in several hundred hours of use, it has never missed a beat.

A few added comments/suggestions:

1 - Proper antifreeze level? any evidence of leaks?

2 -Can you replicate the problem? We had an experience where we overheated for no apparent reason, we suspect that we had sucked some seaweed towards the strainer & when we shut her down, it dropped away. Problem self resolved. Make sure you have an actual overheat issue & you're not chasing your tail.

3 - I heartily recommend adding an actual temperature gauge if you don't already have one. We cruise at 2,9000 to 3,1000 RPM ~6 knots. Temp is the same as if we were running at 2,000 RPM. If we push her to max throttle 3,500 rpm (woods hole against the current for example) the temp will run up 10-20 degrees.

4 - regarding the "over prop" issue - what is the max RPM you can get the engine to turn under power? As others have mentioned, should be w/i 10% of 3,600 rpm. If you can't get to rated rpm, don't immediately blame the prop, we've had an issue with a bent shaft/strut (hung up on empty mooring next to ours during storm) "robbing" power.

Hope this helps.


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## JohnRPollard (Mar 26, 2007)

Hazmat,

Great first post! Between you, Melrna, Camaraderie, and others, this is turning into a great checklist for the Yamar 3GM30F.

Your point about replicating the overheat is a good one. Sometimes it is just anomolous. But it's probably good to run through the checklist anyway.


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## badsanta (Oct 16, 2006)

I have the 3gm30 and am getting black sooty smoke after 2400 rpm. new exaust elbow, filters, replaced injectors. adjusted the valves and still the same. 
Compression test #1-500psi #2-400 and #3 is 410. was told that a new 3gm30 wont get over 460psi so either its something else or the gague is wrong. So if the gague is off it's about 8% off so that brings down my loest psi to the 360 ish range and I see a problem.. 

Question? Time for a rebuild? if so who? or can this be done with a book and a rebuild kit, or should I upbrade to the yanmar replacement what ever that is. Many thanks for the help


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## PilotAlso (Nov 25, 2007)

To address the overheating issue of the original poster, is it possible the water pump drive belt is slipping?

It would make sense that as the rpm's built up there would be more strain on the belt as the impeller moved more water. If the belt tension was a little light, it could slip while turning at higher rpm's and grip again with less strain.

I run my 3GM30F at 2800-3000 rpms. It starts to smoke a little after that and I'm nearing hull speed anyway.


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## TSOJOURNER (Dec 16, 1999)

With all the symptoms you have posted over the last month, you may very well be at that rebuild vs. new question. Unless you are an experienced diesel mechanic, I wouldn't recommend trying to rebuild it youself. When I had mine rebuilt this summer, the parts were about three times the labor cost, and did not include a new crank crank ($900) or connecting rods. 

For the record a re-manufactured engine from Mack boring is about $5200 + freight & installation; I believe a new engine is north of $10,000. Any Yamnar dealer can give you a quote on both options.

If you want more detail contact me thru the IP homeport site

Jim Campbell


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## Rockter (Sep 11, 2006)

With the huge hassle of having to re-build the motor (I did it once, top end, on the Volvo MD17C), I would throttle it back to a constant rev where it did not overheat and leave it at that. 
If you have reasonable starting, and mid-range power, I would not touch it. Throttle the older motor back until it is at ease with it, and stay there.
Although 86 % of full load sounds OK for a newer motor, I would not rev the old Volvo to more than 2000 rpm for any length of time. It will take flat out for a wee while, but I don't push it, and that is with the top end rebored and valves re-cut, and collant jackets de-scaled.


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## Rockter (Sep 11, 2006)

Sorry, 2000 rpm is 80% of full revs.


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