engine issue? prop? nothing? help!

[Bullshooter]

Originally Posted by j.g.evans

I had an engine that would die under load and even stop. After restarting it would run awhile. My problem turned out to be rust flakes from my iron tank that would restrict the pick up tube. When the engine stopped the flake would fall away. The flakes were too big to get to the filter so the fuel always appeared clean. My solution was to replace the tank.

This. All good suggestions, but similar to the above happened to me (but on an aluminum tank), and especially if your pickup tube is near the stern end of the tank, it would suck up the flakes when in forward gear.

For diagnosis, I like this suggestion from Denallan for ease of testing:

Fuel starvation.Had same problem on previous boat,fine at3000 in neutral,would slowly dropto 800 rpm in gear.After much searching found a mostly collapsed fuel line between tank and racor.The line looked new on the outside.You can test for blocked vent by opening fuel filler cap while experiencing the problem.You can also check for starvation by temporarily hooking up a spare outboard tank(with diesel of course) directly to your lift pump to rule out tank,lines,filters.I replaced my lines and never had the problem again.

[MEC]

At the time Catalina manufactured this boat they had the practice to fit a small stainless steel mesh "basket" on the tip of the fuel pickup. This wire mesh filter never gets service because most owners don't know the filter exists.


By now the mesh is fouled and plugged with high viscosity sludge and has likely collapsed. This explains why the engine runs well at idle no load but fails to deliver HP under load.


Polishing the fuel tanks won't clean this mesh filter.


It is best to remove the mesh screen filter from the pick-up tube. When you do this, inspect the tube interior to make sure it is not fouled.


When doing this remove the tank vent line at the tank port and verify that the line is clear so the tank is well vented.


Add 5 or 10 gallons of fresh diesel to the fuel tank.



Change your primary diesel fuel filter element (Racor). Fill this filter with fresh clean diesel before securing the filter cap. Change the engine mounted fuel filter. Bleed the fuel system until diesel weeps out of the bleed port on top of the engine mounted filter. Start the engine and let it idle for 10 minutes to verify that the fuel system does not have any air pockets. If the engine stops during this test, repeat bleeding process and retest engine.



Sea trial the engine after you have established that the fuel system has no air trapped.


I bet you will find that the problem has been eliminated.


By the way, the Cat 36 is under-powered. So steaming under adverse headwind and current will severely reduce boat speed and performance compared to steaming under slack wind and tide conditions.


I hope this information is useful.

[donradcliffe]

I fixed a Catalina 34 with the same symptoms. In this case the blockage was in the fuel pickup line elbow just outside the tank. I did check for a wire mesh screen on the pickup tube because I too have seen those clogged, but this boat either didn't have one or it was previously removed. The blockage was small round pellets like drywood termite droppings, which I have seen in other fuel tanks.

[Bullshooter]

I would add that the test described below performed at the start would establish whether fuel or its delivery is the problem:

You can also check for starvation by temporarily hooking up a spare outboard tank(with freshdiesel of course) directly to your engine to rule out tank,lines,filters. I replaced my lines and never had the problem again.

[Dockhand]

I have seen this several times, sounds like the strainer on the end of the pickup tube in the fuel tank.

[desodave]

Originally Posted by Airyella

Thank you everyone for the replies. I checked the filters and saw no issues; topped up tank to almost full, added some seafoam, tested her in gear with the mooring lines tied astern to replicate some load, then headed out - no problems at all. We are due for a tank cleaning and polish but whatever happened the other day appears to have been related to the conditions primarily. Thanks again for the advice!

Personally I'd check things a bit further. I've gone through the same problems and they always happened under the worst possible situation, and it sounds like your testing didn't replicate that. In my case that was usually bringing the boat back into the marina which is off Discovery Passage, where currents run at up to 8-9 knots. That means coming in on an ebb (current with you at least and not at peak) but often against a 15-20knot wind gusting in the Passage ( = really rough and turbulent).
All of the suggestions so far are great, but two other points.
Running on a tank less than half full allows the fuel to really slosh around and stir everything up. I took the cover plate off the tank and we used a small drill powered pump to carefully suck out the fuel from the bottom of the tank, after it had sat at the dock for a few days. There were a few visible particles resting on the bottom of the tank. I also discovered that I had used 2mm Racors rather than 10mm for the primaries - they were likely clogging on the smaller particles really quickly - but looked fine on inspection - and the secondary filter was doing little to no work

And with full paranoia in place, I now never come in with less than 2/3 of a tank of fuel. I fuel up at a nearby marina outside the Passage if I have to.

[john manning]

I agree with the other posts here that fuel starvation was the most likely cause. However you also need to check the air supply to the engine.

In one case where I had to repair a launch engine with intermittent low rpm, after many hours I found a lump of debris in the tank was coming up against the outlet pipe and staying there until the fuel flow would drop away, when the debris would clear away from the pipe and the engine run normally again.

[Dockhand]

Your listing you installed a 2 micron filter, if it was plugging it would just get worse and worse, not intermittent. Plus if the 2 micron filter is plugging its showing you have contamination in the fuel tank and it needs to be cleaned. I wouldn’t want to need full throttle and not have the power, you could endanger yourself and someone else.

[Tanqueray]

Lots of good suggestions already posted. I will add that my John Deere tractor would start coughing and cut out after 20 minutes or so of use...happened several times. I pulled the fuel filter, but not plugged. But it would start right after that.

Turns out the vent in the cap was plugged up, so after about 20 minutes, it would not be able to overcome the vacuum and deliver fuel... when I pulled the fuel filter off, that broke the vacuum (I could actually hear fuel running back into the tank), and the engine would run again. For about 20 minutes.


So, the fuel tank vent, as mentioned could cause the symptoms you are having. Fuel pickup tube plugged, filters plugged, all seem like things to check.

Good luck,

Greg

[Uncle Bob]

Originally Posted by donradcliffe

I fixed a Catalina 34 with the same symptoms. In this case the blockage was in the fuel pickup line elbow just outside the tank. I did check for a wire mesh screen on the pickup tube because I too have seen those clogged, but this boat either didn't have one or it was previously removed. The blockage was small round pellets like drywood termite droppings, which I have seen in other fuel tanks.

Sounds like asphaltenes, been there done that . Regular dosing with a fuel additive and tank filtering has solved it for me.

[Icarus]

Fuel blockage or failing fuel pump, inspect and clean the fuel lines and tank.
I had a similar problem and found that the fuel suction pipe fitting at the small shut off valve was nearly blocked shut over the years by dirt in the diesel fuel.

[Sailnutdan]

I had a similar issue. After months of checking things, we finally noticed that the seal on the fuel filters was too tall or short (can't remember it was a long time ago) preventing from getting a good seal. Just barely noticeable, and as we had disposed of the old ones we had nothing to compare. But after replacing them a second or third time we found it. The filters we purchased were the exact same manufacturer and number and filter size itself same color and size, just the rubber seal was a little different. These were internally housed filters, not sure what you have. Very frustrating but always worked below 1500 rpm, or faster initially. After replacing, never had an issue since.

[LeighWebber]

Upvote for partially clogged fuel filter(s). A bit of tech: the throttle control on your engine does not set the amount of fuel the the fuel injection pump delivers. The throttle is connected to the governor, and tells it what RPM to strive for. The governor then manipulates the fuel injection pump to deliver more fuel until the desired RPM is reached. This means that in neutral, you can open up the throttle wide, but the amount of fuel being delivered will be low, because the governor will reduce the fuel flow when the desired RPM is reached. This is why the problem only shows up under load. You ask for, say, 2600 RPM, and the governor tries to increase the fuel flow accordingly, but due to a partially clogged filter, the required fuel flow cannot be achieved. In other words, the fuel flow rate depends on the engine load (as well as the throttle setting).

[Paradox111]

Due to age of an electric lift pump, it may be limiting fuel delivery at higher rpm.

[r2sail]

I once had the fuel supply line coming out of the tank get clogged and of course it shut down for fuel starvation, disconnected the fuel line at the tank nothing came out used a solid copper wire from house wiring to poke clean and fuel started flowing