Yanmar 3GM30F tough starting (runs well)

Sep 12, 2019
23
Hunter 335 Seattle
As topic mentions my 3GM30F runs great once you get it started. It takes a lot of throttle and cranking to get it to start. At that point (expectedly) a bunch of smoke comes out of the exhaust before it settles down. Once you've run it a bit it has no problem restarting, it's mostly a cold start after a day or so of not running.

I had a diesel guy redo all my filters, bleed the system and check on the impellers, but still the same issue. He didn't seem to have any insights. Curious if anyone here has thoughts on how to make it start more easily?

Thanks!
 
Sep 25, 2008
7,077
Alden 50 Sarasota, Florida
Diesels require only three things to start - fuel, air and a place to exhaust both. Assuming compression is good and good running implies you have the first two, we can only guess it’s the third. . My guess is you haven’t inspected or cleaner your exhaust elbow.

Second guess - your “diesel guy” wasted time (read - your money) on filters and impellers which have nothing to do with starting an otherwise good running engine.

My suggestion - Check the exhaust elbow and find a better diesel mechanic.
 
Sep 12, 2019
23
Hunter 335 Seattle
I'll check the exhaust. Once engine is running seems fine. Diesel guy did what was asked basic tune up after two years.

I've seen some info about fuel injectors being a possible culprit, but those seem to be more likely an issue while running, not on start and then go away?

On the exhaust elbow - what is it I'm looking for? Internal corrosion / build up?
 
Sep 25, 2008
7,077
Alden 50 Sarasota, Florida
I'll check the exhaust. Once engine is running seems fine. Diesel guy did what was asked basic tune up after two years.

I've seen some info about fuel injectors being a possible culprit, but those seem to be more likely an issue while running, not on start and then go away?

On the exhaust elbow - what is it I'm looking for? Internal corrosion / build up?
If your engine is only two years old with normal use, it’s likely not the exhaust elbow. However, if it’s older and never inspected, your symptoms indicate it’s clogged requiring removal and inspection/cleaning.
 
Sep 12, 2019
23
Hunter 335 Seattle
Thanks - will check. Engine is 30 years old, I was commenting on the work requested of the diesel guy, just tune up.

Seems a reasonable DIY job, I'll take a peek.
 
Jan 7, 2011
4,727
Oday 322 East Chicago, IN
Diesels require only three things to start - fuel, air and a place to exhaust both. Assuming compression is good and good running implies you have the first two, we can only guess it’s the third. . My guess is you haven’t inspected or cleaner your exhaust elbow.

Second guess - your “diesel guy” wasted time (read - your money) on filters and impellers which have nothing to do with starting an otherwise good running engine.

My suggestion - Check the exhaust elbow and find a better diesel mechanic.
Don, how does a plugged or restricted elbow manifest itself ?

You are suggesting it could affect the starting. Once the engine starts, it sounds like it runs OK. Would that be the case with a plugged elbow? Would it be impact the exhaust water stream (volume or temperature or ???)?

My 2GM20F starts fine (a little more work when it is cold or has sat for a long time), starts really well if I use it everyday. My exhaust water temperature is very tepid. barely above ambient water temp. Flow seems fine.

I have owned the boat for about 6 years, and believe the elbow is original. I am in fresh water (boat has been in fresh water since it was built in 1988).

I don’t want to tear up the exhaust hose, break the studs on the exhaust manifold, etc. for no reason. M

The ONLY issue I have is when I run the engine WOT, I get unburned fuel in the exhaust (looks like black soot in the water).

I am assuming this is not a manifestation of a plugged elbow, but curious what your take is.

Greg
 
Apr 22, 2011
865
Hunter 27 Pecan Grove, Oriental, NC
I had a severely blocked exhaust elbow on a 3gm. It started up fine, but would overheat at high power settings.

My present boat has a 2gm that had starting problems when cold. Turned out to be an injector leaking into the cylinder after the engine sat for a while.

You should also look for a slow air leak in the fuel line between the tank and high pressure pump.
 

Ted

.
Jan 26, 2005
1,254
C&C 110 Bay Shore, Long Island, NY
What is the air temperature when you have difficulty starting the engine? On cold days try pointing an electric hair dryer into the air intake before you crank over the engine. (If you have access to shore power) Heating the fuel lines would also help.
 
Last edited:
Sep 25, 2008
7,077
Alden 50 Sarasota, Florida
Don, how does a plugged or restricted elbow manifest itself ?

You are suggesting it could affect the starting. Once the engine starts, it sounds like it runs OK. Would that be the case with a plugged elbow? Would it be impact the exhaust water stream (volume or temperature or ???)?

My 2GM20F starts fine (a little more work when it is cold or has sat for a long time), starts really well if I use it everyday. My exhaust water temperature is very tepid. barely above ambient water temp. Flow seems fine.

I have owned the boat for about 6 years, and believe the elbow is original. I am in fresh water (boat has been in fresh water since it was built in 1988).

I don’t want to tear up the exhaust hose, break the studs on the exhaust manifold, etc. for no reason. M

The ONLY issue I have is when I run the engine WOT, I get unburned fuel in the exhaust (looks like black soot in the water).

I am assuming this is not a manifestation of a plugged elbow, but curious what your take is.

Greg
First and most important, I’m not a diesel mechanic or offering anything more than my limited experience with similar issues over the years. While I understand completely tearing into the elbow isn’t a quick job and shouldn’t be necessary on a 6 year old engine, the description is a classic example of a restricted exhaust.

The first sign of an elbow problem manifests itself when starting rather than running. Diesels need to ‘breathe’ more when starting when the exhaust back pressure is more critical compared with a running engine which is generating more positive exhaust pressure.
 
Jan 4, 2006
6,444
Hunter 310 West Vancouver, B.C.
Try turning over the engine for about 15 seconds with the stop pulled. This will get the rings oiled and provide good compression which is vital for starting. Watch you don't overflow your muffler. How does your engine start following a previous day of running ? The rings will still be wet after one day and you should still have good compression.

If the engine is 30 Y.O. and you don't know for a fact when it was last checked, it needs to be checked TOMORROW. Can't say that would be my first choice for starting problems (although it's still up there).

This is what you might expect to find:

Dirty Sectioned Mixing Elbow.jpg

It's what I found in mine.
 

HMT2

.
Mar 20, 2014
899
Hunter 31 828 Shoreacres, TX
I have a 35 year old Yanmar, if the outdoor temperature is lower than about 50 degrees, she starts just like yours. Above fifty or so degrees and she fires right up. Try the hairdryer trick Ted talks about . I have never been too concerned about it because the number of days I go sailing with a temp below fifty are not many.
 
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Jul 23, 2009
857
Beneteau 31 Oceanis Grand Lake, Oklahoma
Don't forget to check the battery and the cable connections on both ends. Cranking speed is critical for diesel engines when cold starting. Don't take my word for it, Google it.

Does it have glow plugs? Are they working?

Also try a double dose of Power Service diesel additive in the silver bottle.
 

RoyS

.
Jun 3, 2012
1,739
Hunter 33 Steamboat Wharf, Hull, MA
Yanmar tractors often use a Thermostart (not thermostat!) device for cold starts. This acts like glow plugs for engines not equipped with glow plugs. It heats the air in the intake manifold with a diesel oil drip flame. Each start uses about two drops of fuel. I have it on my 2QM15 and it works perfectly. Just apply power to it for 20 seconds before a cold start and you will start almost instantly. The device is inexpensive and readilly available. It screws into an existing port (on my 2QM15). Fuel is maintained in the small reservoir over the device by the injector return line. I have used this for years without it requiring any service. You must wire in a button to operate the Thermostart. I used a separate Yanmar start button I installed next to the engine start button and it is powered by the same circuit. photo attached.
E9F162D9-936E-40BA-83D6-B9F5F60F8C6D.jpeg
 
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Jan 5, 2018
187
Hunter H34 0828 New Orleans
How did u plum this in?
2CCCE7A0-6A91-4D4D-9E8B-8027C670F371.jpeg

Yanmar tractors often use a Thermostart (not thermostat!) device for cold starts. This acts like glow plugs for engines not equipped with glow plugs. It heats the air in the intake manifold with a diesel oil drip flame. Each start uses about two drops of fuel. I have it on my 2QM15 and it works perfectly. Just apply power to it for 20 seconds before a cold start and you will start almost instantly. The device is inexpensive and readilly available. It screws into an existing port (on my 2QM15). Fuel is maintained in the small reservoir over the device by the injector return line. I have used this for years without it requiring any service. You must wire in a button to operate the Thermostart. I used a separate Yanmar start button I installed next to the engine start button and it is powered by the same circuit. photo attached.
View attachment 188835
 
Sep 12, 2019
23
Hunter 335 Seattle
You should also look for a slow air leak in the fuel line between the tank and high pressure pump.
Heritage - How do you recommend I look for the leak? Thanks for the tips.

So far I have: look at exhaust elbow, look at fuel injectors, and check for a minor air leak in the fuel line. Will try and let you know what I find.

As to other Qs - it usually starts quickly after running for a while. The closer to last run, the quicker it starts. After a day it takes maybe three, four seconds of cranking as opposed to 20.
 

HMT2

.
Mar 20, 2014
899
Hunter 31 828 Shoreacres, TX
SIr , it is the cold and no glow plugs see post 14 & 8.
 
Dec 19, 2006
5,809
Hunter 36 Punta Gorda
Check mixing elbo and mine would not start at all after winter storage and after replacing mixing elbo
it would start real easy.
Nick