Diesel advice needed

RAD · Sep 3, 2012

Clogged injector was the first thing that came to my mind and then it unclogged it self? do you add any type of fuel additive to help keep the injectors clean? I alway buy my fuel from a busy truck place and transport it in 5 gal's containers and I only have 24 gallons to fill up so its not bad but when I travel and fill up I'm always worried I'll get a tank full of crap

Dan Hill · Sep 3, 2012

I'll go with the fouled prop theory. Time heals all wounds but it usually doesn't apply to mechanicals.

RichH · Sep 3, 2012

Possibilities, although the 3QM isnt all that sensitive to minor amounts of air in its fuel delivery system:

1. When you changed the filters you didnt purge all the air from them, it take some time for such filter media to fully saturate with oil ... the residual air gets trapped in the top of the filter housing, etc. there to 'slug' into the injector system later or when the boat is heeled over.
2. If this happens again and soon, look for air leaks at the filter assemblies and 'wet-out the filter's gaskets to ensure a positive air tight seal. You changed the filters two weeks ago ... therefore there is a high probability that the filters were installed without a positive seal (dry gaskets, etc. instead of lubricated/oiled gaskets, etc.)
3. Inspect any 'compression fitting' in the system for signs of leakage ... compression fittings are really a one-time only tightening device ... and the copper tube under the 'ferrule' should be trimmed each time you reopen the compression fitting.
4. How long ago did you fill the tank? A high delivery fuel source can entrain lots or air and 'oil foam' in the oil ... and the air bubbles can become temporarily entrapped in
'high spots' in the fuel delivery system ... and be released later as the boat pitches, rocks, heels, etc.

The signs and symptoms are typical of an air leak or a 'slug of air' .... if this continues, run the engine at WOT and immediately shut off the tank valve immediately foillowed by the engine ... and watch how soon it takes for the vacuum gage(s) on your filters to return back to zero vacuum. A 'solid' system (intact gaskets, intact compression fittings, and lift pump diaphragm, etc.) will take a looooong time (hour or more) to return to zero vacuum on a filter gage when the tank valve is closed during high load on the engine.

Johnb · Sep 3, 2012

I had strange intermittant episodes of loss of power that eventually went away after I changed out the cam shaft driven fuel pump on my 3 QM (1983). Its the small one on the starboard side low down and toward the bow end of the engine - the one you pump by hand to bleed the system.

This is not a very expensive item and pretty easy to do. I don't recall if a new gasket came with the pump but I figure you should have one on hand if you decide to do it.

Weasel · Sep 3, 2012

Check your exhaust discharge elbow off the engine. If it is the "U" type and plugged with crud pitch it and get a new one. The SS ones can be cleaned. Worth checking out, Yanmar told me these should be checked every 200 hours.

rasselas · Sep 4, 2012

Fuel filter. Mixing elbow.

Alice A. · Sep 4, 2012

Banjo bolts

rasselas said:
Fuel filter. Mixing elbow.

This happened to us earlier this summer. Both banjo bolts needed tightening. Our engine is a 3HM35F.

Jack4873 · Sep 4, 2012

I had a nearly identical issue with a Universal Westerbeke in a Catalina 350. Brand new filters, including a 20 um Racor and a 2 um secondary filter. Turned out to be a warm weather gel similar to Vaseline that gummed up the fine mesh secondary filter and blocked it significantly. Like you, I've bought fuel from the same source and apparently I'm the only one who had an issue. We cut the filter open to examine the paper element to verify the issue. Replaced the fuel and added a popular truck fuel additive and it's been fine since.

Maine Sail · Sep 4, 2012

Could be a simple as sucking air into the pick up? If the tank was not full and the pick up an inch or so off the bottom when motor sailing it could have "sloshed" and sucked some air. Some pick ups are not centered in the tank and I know a few boats that will suck air when motor sailing with as much as 1/2 tank or more..

Richard Bryer · Sep 4, 2012

Must be something in the water around Toronto, Higgs- I am having same problem. However I am very certain it is air in the system as I ran out of fuel on my way back from our trip this summer ( bad math!). Sucked in lots of air before I got it started. Thought I had it all bled out and went for a 1 hour run on motor. about 20 min out ran into same thing- a drop of about 1000 rpm, engine kept running, then worked its way back up in about 60 seconds. Did it 4 or 5 times. I bled it again at the dock- this time found I had a broken bleed screw- the little screw had broken about 1/2 way down its length. Replaced and bled again. runs ok at the dock but haven't been out to check under load and for a longer run.

Navicula · Sep 4, 2012

Maine Sail said:
Could be a simple as sucking air into the pick up? If the tank was not full and the pick up an inch or so off the bottom when motor sailing it could have "sloshed" and sucked some air. Some pick ups are not centered in the tank and I know a few boats that will suck air when motor sailing with as much as 1/2 tank or more..

I like what he says.....................think of the simple things........this happen to me last night in big swells, I am sure of it.

NotCook · Sep 4, 2012

When we have air in the fuel we have just the opposite sympton. Our Perkins Ranger 6-135 will speed up a few hundred RPMs. When it does, I know it is about to die in just a few seconds. It absolutely does not tolerate any air in the fuel line. So, it is interesting to me that you are encountering a drop in RPMs. I vote for the clogged injectors. I would think something fouling the prop would probably set up a significant vibration.

Bill Glass · Sep 4, 2012

Loss of power

Elbow..... same thing happened to us. Replaced.

seadaddler · Sep 4, 2012

LowFuel

Maybe tank was low on fuel or picked some thing clogging the fuel filter.
nick

nutheastah · Sep 4, 2012

Diesels since 1969. stopped in 2001 because I developed an allergy to the fuel. so I do other things now. things I'd want to know to figure this out. How long had the engine run since you fueled up? was it making any black or white smoke? did you try to get full RPM in neutral? were you doing anything to the engine when the power came back? Bad fuel problem most likely wont go away. Black smoke from lack of air, white smoke from stuck injector. Lack of power can be lack of fuel or something affecting throttle linkage. on Mack trucks the lever on the Injection pump had tension springs which would wear out and cause this type of sympton. also check to make sure that throttle linkage isn't being restricted from going to full throttle especiall under healing conditions. A diesel can get full rpm in a no load situation even when the throttle hasn't maxed out. I'd rule out evil spirits, anything mechanical is subject to failure ( rule # 4 of absolutes after death taxes and nice guys coming in last) I would look for things like a pinched fuel line, worn or loose linkage or a rag in the fuel tank before I started to buy parts.
Bruce

captainpat · Sep 4, 2012

Many boats have a screen in the pick-up tube that can clog if there is gunk in the tank. It's one of the easier things to check. I had a boat that would suck up globs of jelled algea at times - of course, usually the worst times! Siphon out the fuel from the bottom of the tank and you will see right away if the tank is dirty. Clean tank and fuel and remove the screen in the pick-up tube.

SailingHarry · Sep 4, 2012

If your Racor is a 200 series -- looks like this: http://ep.yimg.com/ca/I/yhst-16516676850439_2203_3781083 -- then the internal pump can cause a blockage that will sporadically slow (or kill) the engine. Took me a year to figure it out. Solution? Screw down the pump "knob" when you are done pumping.

Harry

bentwing60 · Sep 4, 2012

Check-change the air filter anyway, Higgs. Got a 99 C-320 with a 3GM30F and the wire backed foam filters go south about every 4 years or so. Supposed to be checked and re oiled yearly, but most don't RTFB so the foam dries out and crumbles and is eaten by, you guessed it, the engine. Mixing elbow probably also needs attention , as they do coke up and restrict exhaust flow. Wouldn't question any of the other posts relative to fuel, as it is the most common problem encountered with these small diesels.

terrykiwi · Sep 4, 2012

It seems strange to think that it may be filters as the problem went away after 1/2hr and hasn't come back again. Gunk in the fuel tank even after having it cleaned out 2 years ago is a possibility but unlikely. If it was air in the fuel system you would think that the engine would have a miss that would be noticeable during the event. If the throttle lever has a break over spring this could be weak. Check that you are getting full throttle at the pump. As you say you may have gotten a fouled prop which is possible also and knowing what floats out there I'm not surprised. 2 months ago I purchased me Beneteau 381 from Whitby and you should see the crap that floats around in the Marina. I delivered the boat 1 week after purchase to Georgian Bay with no problems 102hrs on the engine and 500nm I didn't change filters before I left so some one was on my side. The filters were still serviceable even after they were changed. Thats my 2 cents worth. Good luck