Yanmar 3GM30f hard starting

[lateral]

Racor primary filter with hand Primer on top.
Standard Yanmar secondary filter.
600hrs over 20yrs. barely used, sat idle for 10yrs

Within the last year serviced heat exchanger system incl elbow, injector pump, new lift pump, all fluids etc.
Started really well initially, now reverted to old symptoms.
Now if it sits for a time it is hard to start and have to keep overcranking until it catches. Then it is easy to start for rest of the day.
Power normal , tops out at 2800rpm though.

Can air get in if there are no visible diesel leaks?
Guess compression test should be next.

[topmast]

Same problem on old ford trucks Fuel drains down when stopped. The return lines can suck a bit of air even if they show no leak when running, Return dumps back into system at filter so it adds up .So hard on batteries and starter.

[a64pilot]

Yes, it is called loss of prime. It is a pretty common problem with Diesels.
If your sure all lines etc are good, then it could be the manual pump.
It took me awhile to find it on my Truck, ended up being the air bleed screw O ring, since the filter is on the suction side it didn't leak any Diesel at all, but being under vacuum it did let air in.

[lateral]

Originally Posted by a64pilot

Yes, it is called loss of prime. It is a pretty common problem with Diesels.
If your sure all lines etc are good, then it could be the manual pump.
It took me awhile to find it on my Truck, ended up being the air bleed screw O ring, since the filter is on the suction side it didn't leak any Diesel at all, but being under vacuum it did let air in.

Thanks, always have been suspicious of the racor. I may try a bypass temporarily.

[gamayun]

I had similar issues - it would click but not turn over when the engine was cold, but it worked fine after it had warmed up - so I added a starter relay. It's still a bit sluggish on cold startups, but no longer is there just the click.

[topmast]

Different issue. Initial diagnosis is fairly important

[sailorchic34]

The banjo bolts on the lift pump and engine mount fuel filter can vibrate a little loose on the GM engines. Always good to check that they are snug every 100-200 hours.

When running a GM at idle, pull each decompression lever one at a time. They should all have the same chug chug sound. If one has a different sound, less strain. then that cylinder may have "issues". If they all sound the same it's probably not compression.

If one sounds off, with the engine at idle, remove the oil fill cap. IS there a hiss of pressure being relieved or grey smoke coming out the oil fill. Either would be an indication of bad rings.

Yanmar has issues with the 1994 piston in the GM engines where the rink lands would sometimes break.. From my very personal experience, hard starting and smoke out the oil fill is broken rings.

At 600 hours a 3gm will measure as new with no apparent wear. It's just getting broken in.

Could also be a bad lift pump, clogged dip tube, colapased hose or clog in the fuel line.

Odds are it's a very annoying vacuum leak in the fuel system. Those are the hardest to find. I just redid my entire fuel system piping from tank to engine filter. Fixed that little problem once and for all.

[bailsout]

Similar behavior from my 2qm15.
Solution turned out to be fuel distributor timing with correct shim.

[Liam Wald]

Originally Posted by sailorchic34

The banjo bolts on the lift pump and engine mount fuel filter can vibrate a little loose on the GM engines. Always good to check that they are snug every 100-200 hours.

When running a GM at idle, pull each decompression lever one at a time. They should all have the same chug chug sound. If one has a different sound, less strain. then that cylinder may have "issues". If they all sound the same it's probably not compression.

If one sounds off, with the engine at idle, remove the oil fill cap. IS there a hiss of pressure being relieved or grey smoke coming out the oil fill. Either would be an indication of bad rings.

Yanmar has issues with the 1994 piston in the GM engines where the rink lands would sometimes break.. From my very personal experience, hard starting and smoke out the oil fill is broken rings.

At 600 hours a 3gm will measure as new with no apparent wear. It's just getting broken in.

Could also be a bad lift pump, clogged dip tube, colapased hose or clog in the fuel line.

Odds are it's a very annoying vacuum leak in the fuel system. Those are the hardest to find. I just redid my entire fuel system piping from tank to engine filter. Fixed that little problem once and for all.

Terrific answer.
Sailorchic34, you rock.

[seasick]

I second Sailorchic's diagnosis of bad rings and lack of compression. Yours are classic symptoms of this.

[DeepFrz]

Your symptoms could also indicate a bad start battery that is weak. It could have trouble spinning your engine when it is cold. After it initially starts your alternator charges the battery, the engine warms up making it easier to start. Just one more thing to check out. You can check the battery voltage at the starter terminals when cranking cold and then after warm up. Wouldn't hurt to check and clean all of your battery connections as well.

[JD-Odyssey]

You mentioned all the upgrades you did to the engine itself. Did you clean out the fuel tank and are you sure you have good clean fuel running through the filters? If the tank was never cleaned well after years of sitting, there could be gunk that's coming loose and being pumped through your feed lines. I picked up some bad fuel two years ago which clogged my filters with jellied fuel. The heat from the engine tended to increase the flow but when the engine cooled down, it was very difficult to start again.

[Stu Jackson]

There are probably more "Yanmar hard starting" topics on this and all other boating forums than there are people in China!!! Really. A little searching, here or on Google will give you the answers in addition to sailorchic's superb response. If it's not the fuel system, then gamayun's answer is the one most replies lead to as a solution. sailboatowners.com had a great writeup on how to do this about a month ago.

[Cheechako]

It could be many things, but the ring problem could be it also. Hard starting, runs up to rpm once going though. I had it happen to two 3GM30's from the early 90's. One at 500 hours.

[sony2000]

I would change or install a check valve on the fuel line, before going much further. The much further maybe a dose of "Seafoam" in the engine oil as well as the diesel fuel.