SO36i Yanmar 3gm30 falters over 2000rpm

[peterb26]

I have a 2007 So36i with a 3gm30 with 700 hours.

On a recent trip I had to run the engine at around 3000rpm for perhaps an hour, maybe more. Until then it had run faultlessly but I normally run it at 2000 to 2500 rpm.

After an hour at 3000 rpm it faltered, then recovered, and then failed. I restarted it later and it ran ok as long as I stayed below 2000rpm.

Back in the marina, I checked the fuel filters (they were as clean as a whistle) and also filled the diesel tank although it was just under half full. The boat has only ever had white diesel installed and it looked perfect when I took a sample, but I also added some "bug treatment" when I filled up just in case.

There was no black or white smoke when it failed - and the engine did not seem to be excessively hot.

After discussion with a few mechanically minded pals, I decided to change the fuel lift pump and did that today.

I then ran it astern on the pontoon at 2500 rpm and within 10 mins it was faltering and losing revs. Didnt actually stop like it did at sea but was quite pronounced.

I checked again when it was losing revs - no black fumes at all - in fact no change to exhaust whatsoever. Exhaust water is quite cool - but I took the top off the small heat exchanger and the water in there was nothing like boiling, I could just about stick my finger in it quickly. Likewise the top of the engine was also hot but not unbearable - so I dont think cooling is an issue.

The only thing I did notice was that I opened the bleed screw on the top of the small round fuel filter while the engine was faltering - and no diesel came out, kind of surprised me?? I then took the filter out and it appeared to be a fair bit less than full, which also surprised me.

I guess all of this points to fuel supply problems, but the tank is full - and the boat is static on the pontoon. I changed the big gravity filter last season and it was as clean as a whistle, and I checked it again back in August when the problem first arose.

Wondered if anyone had any ideas?

Regards and thanks in advance.

Peter

[pbunning]

Have you checked the fuel line from the tank to the filter? We had similar problem a few years ago and discovered fuel line was blocked - actually blocked with black plastic - caused by company who fitted eberspacher, drilling directly into the tank and not removing the cuttings. Understand this had also happened to other boats.

[peterb26]

thanks for that pb .
tomorrow I am going to rig up a "temporary diesel tank" using a can and feed that into the inlet side of the lift pump. If that works ok I know the problem is somewhere before the lift pump and will start taking that lot to bits again.

[Donrob]

Something similar happened to me on my 75 hp Yanmar 4JH3-TE at beginning of season soon after a full engine service. I called the Yanmar people in again and they checked the fuel line from tank to fine fuel filter and there seemed to be nothing wrong there. They also checked the breeder and it was not blocked. They looked at the filters (changed just a couple of weeks before) and they decided to replace the course fuel filter (ie the one between the tank and the engine) and still it was faltering on high revs. Finally they replaced also the fine fuel filter on the engine and the problem was resolved. They believe that either this last filter was defective or that there must have been some blockage that cleared itself. They advised me to put in a diesel additive every time I fill in diesel because sometimes it is not clean. I had no more trouble after that even on 3500 revs.

[bill42i]

Hi Peter,

I had identical symptoms early this year and went through all the same filter changes etc. that you did. Finally, in desperation, I removed the pick-up pipe from the tank (three screws through the metal plate that surrounds the rigid pipe where it enters the plastic fuel tank). The pick up pipe terminates in a course mesh filter and this was blocked by black slime (dead diesel bugs). I removed the mesh and fitted an in-line filter, before the water separator. No further problems!

[Donrob]

By the way I forgot to mention that before this problem started I had a leak in the exhaust muffler and had this taken out for repair (quite a job). To do this the diesel tank had to come out too and so I took the opportunity to have it power washed from the inside to remove any sludge and so I knew that this was not causing the problem.

[peterb26]

Sorted!

Here is what I did.

a) Fitted new lift pump - idiot me as it was obviously fine, still at least I have a spare now....

b) Fed the lift pump input from a can of diesel and immediately it ran fine. So problem around tank and main filter.

c) Took tank suction tube (ie input to main filter) out. it has metal filter on the end and that was a bit dirty but not too bad.

d) Fed the lift pump direct from the tank with no gravity filter in the line. Ran perfectly again,

e) Unbolted the gravity filter from the bulkhead and took it to bits and cleaned out, although it was in good state anyway. Rubber O rings were quite hard which surprised me as they are only 11 months old. Replaced both O rings and fitted new filter.

f) Reassembled and fired up - ran at 2600rpm for 30 mins without hesitation.

conclusion.

- either the hardened O rings caused a leak - or there was a problem with that filter, but it had only run for 28 hours since fitting.

Havent done a sea trial yet at 3000 rpm as that might be too much for ropes on the pontoon!! But remain optimistic..

I post this just in case anyone else has similar problems and may want to go down the same route that I did,

Lastly thanks to all who have helped, once again..........

[rxc]

You say that you "took the tank suction tube (i.e., input to the main filter)" out. I had the "plastic debris" problem, and the plastic was lodged in the hard right angle at the top of the metal suction /dip tube. There was no screen or hose on my tube inside the tank, although I seem to remember that some countries, like the US, have a requirement that there be a piece of hose with a filter on the end of the dip tube. I did not, and still do not have either.

I had to pull the dip tube twice to clean out plastic debris. I think I have it all out now. And the debris was in the tank as it came from the factory - only 116 hours on the engine.

You may end up having to take ALL of the suction line apart, to find the offending debris.

[peterb26]

RXC, I am 90% sure that the problem was related to the primary filter. The steel dip tube that goes into the tank to supply the fuel was not too bad, really only very little dirt on the end and I could blow through it with relative ease. So I suspect either a dodgy C1191PL filter, or the hardening of the rubber seals caused a minor air leak.

But I will bear in mind your comments and thank you.