Yanmar 3GM30F - SailNet Community
LinkBack Thread Tools
post #1 of 31 Old 09-26-2007 Thread Starter
Coastal Cruiser
Bill Mc's Avatar
Join Date: Apr 2006
Location: Hamlet, North Carolina
Posts: 147
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 15
Yanmar 3GM30F

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 Mc is offline  
Sponsored Links
post #2 of 31 Old 09-26-2007
Crazy Woman Boat Driver
Melrna's Avatar
Join Date: Apr 2004
Location: Windward Islands Caribbean
Posts: 839
Thanks: 17
Thanked 18 Times in 15 Posts
Rep Power: 17
Send a message via AIM to Melrna Send a message via Yahoo to Melrna
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!

Last edited by Melrna; 09-26-2007 at 08:40 AM.
Melrna is offline  
post #3 of 31 Old 09-26-2007
Senior Member
JohnRPollard's Avatar
Join Date: Mar 2007
Location: Chesapeake
Posts: 5,680
Thanks: 0
Thanked 4 Times in 3 Posts
Rep Power: 16
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....
JohnRPollard is offline  
post #4 of 31 Old 09-26-2007
Courtney the Dancer
jrd22's Avatar
Join Date: Nov 2000
Location: San Juan Islands., WA, USA
Posts: 3,971
Thanks: 5
Thanked 32 Times in 31 Posts
Rep Power: 20
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.

SV Laurie Anne

1988 Brewer 40 Pilothouse

jrd22 is offline  
post #5 of 31 Old 09-26-2007
camaraderie's Avatar
Join Date: May 2002
Location: East Coast
Posts: 13,875
Thanks: 0
Thanked 7 Times in 7 Posts
Rep Power: 21
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.
camaraderie is offline  
post #6 of 31 Old 09-26-2007
Senior Member
NOLAsailing's Avatar
Join Date: Sep 2006
Location: Mandeville, LA
Posts: 504
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 14
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.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
NOLAsailing is offline  
post #7 of 31 Old 09-26-2007 Thread Starter
Coastal Cruiser
Bill Mc's Avatar
Join Date: Apr 2006
Location: Hamlet, North Carolina
Posts: 147
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 15
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,


Last edited by Bill Mc; 09-26-2007 at 05:22 PM.
Bill Mc is offline  
post #8 of 31 Old 09-26-2007
Senior Member
Join Date: Sep 2006
Location: Scotland
Posts: 2,470
Thanks: 0
Thanked 13 Times in 13 Posts
Rep Power: 14
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.
Rockter is offline  
post #9 of 31 Old 09-26-2007
Warm Weather Sailor
Vasco's Avatar
Join Date: Sep 2006
Location: Toronto
Posts: 1,040
Thanks: 0
Thanked 12 Times in 11 Posts
Rep Power: 14

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.

Rick I
Toronto in summer, Bahamas in winter.

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Vasco is offline  
post #10 of 31 Old 09-26-2007
Junior Member
Join Date: Aug 2007
Posts: 14
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
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.
sailvi767 is offline  

Quick Reply

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now

In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page

Similar Threads
Thread Thread Starter Forum Replies Last Post
Bleeding a Yanmar 3GM30F jlmarra Gear & Maintenance 11 05-24-2017 07:12 PM
Fuel filter replacement on Yanmar 3GM30F gsyversen Gear & Maintenance 7 06-13-2008 02:18 AM
raw water pump leak on Yanmar 3Gm30F gsyversen Gear & Maintenance 24 06-13-2008 01:34 AM
Yanmar 3GM30F prop recommendations, please.. mariner3302 Gear & Maintenance 3 08-18-2006 05:15 AM
Prop for Morgan OI w/ Yanmar 3GM30F cwarwick Gear & Maintenance 1 11-16-2004 01:17 PM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome