Yanmar 3GMF: Mystery Drop in RPMs - SailNet Community

   Search Sailnet:

 forums  store  


Quick Menu
Forums           
Articles          
Galleries        
Boat Reviews  
Classifieds     
Search SailNet 
Boat Search (new)

Shop the
SailNet Store
Anchor Locker
Boatbuilding & Repair
Charts
Clothing
Electrical
Electronics
Engine
Hatches and Portlights
Interior And Galley
Maintenance
Marine Electronics
Navigation
Other Items
Plumbing and Pumps
Rigging
Safety
Sailing Hardware
Trailer & Watersports
Clearance Items

Advertise Here






Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
 Not a Member? 

Diesel This is a new forum dedicated to diesel engines and their applicable accessories.


Reply
 
LinkBack Thread Tools
  #1  
Old 08-07-2011
C-Chelle
 
Join Date: Mar 2009
Location: Hampton Roads
Posts: 4
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
AndrewMcG is on a distinguished road
Question Yanmar 3GMF: Mystery Drop in RPMs

Fellow Sailors, I am perplexed by a drop in rpms on my old (but well maintained) Hunter. Any advice would be appreciated!

I noted a drop in the past year of rpms on the Yanmar 3GMF in my 1985 Hunter 34. After purchasing the boat in 2008 (and during summer 2009 sailing), I noted the engine would rev to 3400-3600 in neutral. Under load and WOT, I reached rpms of 3200+. This would allow us to cruise at about 7 knots.

In summers 2010 and 2011, the boat would still rev to 3400-3600 in neutral, but under load and WOT, rpms would max at 2600-2700. We would still attain speeds of 6.3-6.5 knots. I've had a technician come out and do periodic mantainance (fluids, filters, impellors, hoses, etc.). He noted that the true tach reading was about 500 rpms higher than indicated on the tach.

I have the bottom cleaned several times a year, noted no excess black smoke in the exhaust, and don't have unusual vibration, noise, or difficulty at start-up. I tried to inspect the exhaust elbow, but could not get the hose off easily - i did take the smaller hose off the 90 degree raw water fitting and saw it was clean inside. The elbows and fittings look in new shape (as if they were replaced several years ago).

Given the previous performance - higher rpms and speed - I don't think the cause could be the prop pitch. My current thinking is carbonized injectors, but I would have expected to see more symptoms listed above. Before I make the service call, I would appreciate any comments or similar experiences. Given the options on the boat...no fuel gauge, no engine hours meter...I don't have some of the metrics (fuel usage, etc) that would be helpful!

Thanks very much!
Andrew
S/V C-Chelle
Reply With Quote Share with Facebook
  #2  
Old 08-07-2011
Senior Member
 
Join Date: Oct 2006
Location: Virginia
Posts: 722
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 8
badsanta is on a distinguished road
You will have to remove the exhaust elbow to check it out. They are replaced every few years or so. Unless you changed something I doubt it is your prop pitch unless you hit something with it. First thing I would do is check the prop. you may have snagged a rope or fishing line. It does not take long to have the prop fowled with barnacles this includes your bottom. When was it last cleaned. If it was not last week I would check that first before you start replacing parts.
__________________
That derelict boat was another dream for somebody else, don't let it be your nightmare and a waste of your life.
Reply With Quote Share with Facebook
  #3  
Old 08-07-2011
Senior Member
 
Join Date: Oct 2000
Location: Portland, OR
Posts: 666
Thanks: 1
Thanked 6 Times in 6 Posts
Rep Power: 14
olson34 is on a distinguished road
My guess is....

Based solely on my own limited diesel experience...
I would ask how it's been since the last filter change in your old Racor? (And, did this happen before than time?)

I once had a similar problem that soon progressed to non-starting and it turned out to be a microscopic air leak somewhere in the two O rings or in one of the several plugs in the top of our 1988 OEM Racor filter assembly. Since that model was long ago replaced in the market by a newer model, I replaced it with the current one. Problem solved.

Admittedly this is only a long-range wild guess, but it takes only a very very small air leak to slow a diesel under load.

"Advice virtually rendered to strangers, deposit one virtual cent."

Good luck,
LB
Reply With Quote Share with Facebook
  #4  
Old 08-07-2011
jrd22's Avatar
Courtney the Dancer
 
Join Date: Nov 2000
Location: San Juan Islands., WA, USA
Posts: 3,816
Thanks: 3
Thanked 14 Times in 14 Posts
Rep Power: 14
jrd22 will become famous soon enough
What you have described is pretty typical of a clogged fuel filter as Olson says above. I would change both filters and thoroughly bleed the fuel system and see if that makes any difference before digging into anything else.
__________________
John
SV Laurie Anne

1988 Brewer 40 Pilothouse

Reply With Quote Share with Facebook
  #5  
Old 08-08-2011
Member
 
Join Date: Jan 2010
Posts: 54
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 5
cspaniel is on a distinguished road
Bleed the low pressure (screw over the secondary filter) and report what you get. Does it take a while until it expels diesel? does the diesel have bubbles on it?....continue bleeding if the above is true until diesel with no air comes out and try your engine again. Bleed from the screw at "entrance" to injector pump...let us know.
Abe
Reply With Quote Share with Facebook
  #6  
Old 08-08-2011
Senior Member
 
Join Date: Jul 2006
Posts: 844
Thanks: 1
Thanked 17 Times in 17 Posts
Rep Power: 9
aa3jy is on a distinguished road
..plus check the silencer(air cleaner)
Reply With Quote Share with Facebook
  #7  
Old 08-08-2011
CapitainMike's Avatar
Senior Member
 
Join Date: Apr 2011
Posts: 112
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 4
CapitainMike is on a distinguished road
Check the flexible Exhaust Th interior might be de-laminating.
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Capitain Mike
Mediterranean Sea
Cobra 850
1978
8.68m
"Money won't buy you happiness but it will allow you to buy a yacht big enough to pull up along side it"
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


"Please God be kind to me your sea is so wide and my boat is so small"
Reply With Quote Share with Facebook
  #8  
Old 08-08-2011
leave blank
 
Join Date: Sep 2006
Posts: 128
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 8
EscapadeCaliber40LRC is on a distinguished road
To make sure it is an engine problem, I'd drop off the shaft behind the clutch and run the engine. If the problem goes away something with the prop is not right. Varible props need to be greased periodically. Do you have a varible prop ?
Reply With Quote Share with Facebook
  #9  
Old 08-08-2011
casey1999's Avatar
Senior Member
 
Join Date: Oct 2010
Location: HI
Posts: 2,828
Thanks: 4
Thanked 17 Times in 17 Posts
Rep Power: 4
casey1999 is on a distinguished road
I have a Yanmar 3gmd (30 years old). Runs good except even in neutral I only get to 2700 rpm (based on yanmar tach). In gear and moving at 6.5 knot hull speed the rpm is also 2700. Engine has all new filters and exhaust elbow is good. Exhaust color is normal. Not sure what my problem is either. One thing I have noticed is that when the engine is running I do not have fuel being returned via the fuel return line. I need to look into this more. I am thinking my fuel injection pump is not putting out enough fuel. The lift pump on my engine is new.

One thing is the bleed screw on the top of the Yanmar fuel filter housing has a plastic gasket that can crack and let air in. You may want to replace.

Let me know what you find.
Reply With Quote Share with Facebook
  #10  
Old 08-09-2011
CapitainMike's Avatar
Senior Member
 
Join Date: Apr 2011
Posts: 112
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 4
CapitainMike is on a distinguished road
Quote:
Originally Posted by casey1999 View Post
I have a Yanmar 3gmd (30 years old). Runs good except even in neutral I only get to 2700 rpm (based on yanmar tach). In gear and moving at 6.5 knot hull speed the rpm is also 2700. Engine has all new filters and exhaust elbow is good. Exhaust color is normal. Not sure what my problem is either. One thing I have noticed is that when the engine is running I do not have fuel being returned via the fuel return line. I need to look into this more. I am thinking my fuel injection pump is not putting out enough fuel. The lift pump on my engine is new.

One thing is the bleed screw on the top of the Yanmar fuel filter housing has a plastic gasket that can crack and let air in. You may want to replace.

Let me know what you find.
Some fuel tanks have a filter in the bottom of the tank on the outlet fuel pipe. If you can check the filter could be partially blocked. alternatively and may be also you have fuel lines that are breaking up in side causing a blockage.
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Capitain Mike
Mediterranean Sea
Cobra 850
1978
8.68m
"Money won't buy you happiness but it will allow you to buy a yacht big enough to pull up along side it"
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.


"Please God be kind to me your sea is so wide and my boat is so small"
Reply With Quote Share with Facebook
Reply

Tags
3gmf , rpm , yanmar


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

 
Posting Rules
You may post new threads
You may post replies
You may post attachments
You may edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On


Similar Threads
Thread Thread Starter Forum Replies Last Post
"Drop-in" replacement for Yanmar 2GM scraph Diesel 3 08-15-2011 10:54 PM
Yanmar 2 qm 15 overheating mystery NickAllinson Gear & Maintenance 9 06-26-2011 10:39 PM
Yanmar 3GMF py26129 Gear & Maintenance 2 06-15-2011 01:59 PM
Low RPMs on Yanmar 2GM20 gregw5221 Diesel 15 02-22-2011 04:06 PM
Max Cruising RPMs for Yanmar shopkins Gear & Maintenance 35 04-11-2008 11:54 PM


All times are GMT -4. The time now is 01:35 PM.

Add to My Yahoo!         
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
(c) Marine.com LLC 2000-2012

The SailNet.com store is owned and operated by a company independent of the SailNet.com forum. You are now leaving the SailNet forum. Click OK to continue or Cancel to return to the SailNet forum.