So, a few of you fine gents on this board are familiar with diesels. So my Sabre 34T with its original Westerbeke 30B (1600 hours) motor has developed a weird tendency. RPM's all of a sudden will drop and almost stall the engine. But then pick up again. Sometimes it will actually stall. Almost feels like fuel starvation. Changed both fuel filters. Same issue. Visually I don't see any leaks. Tank is full of fresh diesel. Any thoughts? On top of that an overheat alarm went on today, as I took the boat out to trouble shoot. Not sure if its a a bad sensor, or it as actually overheating. Impeller is fine, and there was plenty of water in exhaust coming out. I did notice a small puddle of coolant under the engine. I am going to keep the boat for a while, so a thought of re-powering it with a new Yanmar even crossed my mind. Or refresh the good ole Westerbeke 30B. Thoughts?
Was there old diesel in there? Did you wash the tank? Could be some crude coming off the walls and getting in every once in a while. Also how about a loose or cracked fitting letting in air? That could be a slight air intrusion. Can you put a clear piece of hose in place of a black piece to see the fuel going into the engine/filters? That can help troubleshoot air leaks in the lines. Do you have a lift pump in the tank? Does it have a filter? it could be not able to supply the fuel needed. When were the injectors last cleaned/serviced? Could be a bad injector. try cracking fuel lines at each and seeing the effect. What kind of intake filter/screen do you have? How is the bottom...have seen some intakes full of marine growth restricting water flow. Is the boat raw water cooled or use a heat exchanger? If heat exchanger look at that for corrosion or blockage. Or maybe the freshwater or raw water pump is bad? Did you check both? If raw water check for blockage or maybe T stat issues...
1600hrs is young. The issues of fuel and overheating are two separate things. Fuel, If you can’t see an external leak a few things could be happening. Pulling vacuum in the tank Crap in the tank floating onto the pick up then dropping when fuel flow drops. An air leak somewhere on the supply side of the fuel system. This is between the lift pump and the pick up tube in the tank. Overheating Just because your flowing raw water doesn’t mean your rejecting heat from the coolant. Raw water is your air/wind in your heat exchange or radiator. Something on the closed or coolant side is broken. Diag it like a car/bike cooling system.
Thanks for ideas, Whats the best way to check the tank for any crud in it? Or best process to clean it? I never services / cleaned injectors. Is there a process for that? Those things are $500 each new. Heat exchanger was replaced a year ago. I wonder if old impeller parts could of clogged something. I had one disintegrate a while back.
Check the raw water inlet side to the heat ex for bits. Also check the outlet of the raw pump. And 90* fittings tend to catch them. Pull the fuel sending unit or inspection plate to look in the tank. DO NOT assume injectors yet! Make sure the supply side is 100% first.
Check your fuel supply hoses as they can collapse inside and give indications as @baconologist described in his first response about debris in the tank. The hose can collapse under suction closing fuel supply, relax, then repeat. I'm reluctant to identify the fuel issue as air in the fuel as this appears to be an intermittent condition. My (limited) experiences with air ingression was running/not running. Not often that it would fix itself then reappear. Overheating: Is the coolant under the engine from the overflow or from the waterpump? If overflow, then I side with @baconologist. If it's directly under the pump, then I believe that it's the pump seal causing the system to leak and prevent pressurization, thereby overheating.
If you’re not running a fuel additive, that’s something you need to consider. Algae will grow inside a diesel fuel tank, especially around an oceanic environment. Running an additive will result in going through a few fuel filters for awhile, until things get cleaned out. If your fuel issues are at idle or very low load, I’d be chasing air passing through the system. I’ve had a supply line crack at a pump fitting, causing low-rpm running issues. Also, I’ve had air leaks at the filter cause the same issues. If the issues are at rpm or under load, I’d be looking at starvation. I’ve seen clogged pickups and lines, from not having a treatment plan. As others stated, your cooling system investigation needs to start at the inlets and any strainers. Gotta’ have a solid preventative plan in place, for every aspect, just like an engineer of a commercial vessel.
Issues are definitely under load and seem to be amplified with higher RPM's. And it does feel like starvation. Probably need to replace fuel filers again, and see what happens.
Rebuilding one is definitely a way to go if that turns out to be a root cause. I looked inside the tank today, and it looked reasonable. Replaced both fuel filters again, and poked at hoses and fuel lines, they seem reasonable. I assume a lift pump is the same as a fuel pump, thing that creates pressure? What kind of shop usually does those re-builds? New that pump is $1,700. Didn't know Westerbeke 30B Three engine parts are made out of titanium. Is there an equivalent Mitsubishi part?
Use the service manual i gave you........geeze Westerbeke uses 2 kinds of electric lift pumps. One look like your standard Facet style gas one for a carb car. The other is a cylinder thats about 2x4”. That on has an internal filter screen, check it too, and the access door seal.
That's the problem with diesel - It's too stable for shenanigans. I accidentally filled a 5 gallon electric vacuum with diesel during a full tank fitting exchange. The only problem was the vacuum smelled like diesel until we threw it away. No explosion, no singed eyebrows, nothing. With the folks that I worked with, diesel fuel prevented the Darwin awards team from reviewing the nomination. Heck, we weld on (full, partial, empty) diesel tanks. I mean it's not smart, but lots of times its necessary.
