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Generator Question

Discussion in 'Generators' started by Kafue, Nov 5, 2012.

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  1. Kafue

    Kafue Senior Member

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    It has been two years this month since I first bought my Hatteras. The generator, an Onan 20kw, ran reasonably well and very occasionally cut out when I was running her or staying on board her in Stuart, USA.
    After picking her up in Newcastle, Australia, I filled all tanks to the brim. The genset would run strongly for hours, while the mains were running or not, but then suddenly cut out. I would prime the fuel pumps, as the generator is fed from the same manifold as the Port main, and the gen would kick back in for another hour or 5 minutes, no telling.

    It gradually got worse, but every time I heard the generator begin to choke, I would turn on the prime pumps and she ran well: This happened on all the tanks. I assumed bad fuel/lines or both. I know the fuel is dirty, I have changed the filters (6 off) twice this year and it is clearing up)
    Asked the local experts, they replaced the generator fuel pump. No improvement. Also, no sign of overheating, she would start immediately after priming. Sometimes she would not stay running from the start of a trip, so no overheating involved. Situation was getting so bad that part of my list to do before the summer season was to put in a new and separate fuel line for the genset.

    However, while I was changing all the impellors, including the generator, I tested her and what do you know….no matter which tank I run off, she will not cut out, even while I start the Port engine, which I would expect, seeing as they are competing for the fuel. So question is: would an impellor make the difference? The old impellor was in bad shape, missing a blade and misshaped.
    Thanks, and being superstitious, I darn well hope that tomorrow she is not back to her old games!
  2. K1W1

    K1W1 Senior Member

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    Hi,

    I am assuming it is the SW Pump impeller you have replaced which has got nothing to do with the fuel system.

    When I started reading your post I was thinking Lift Pump ( the one that supplies the Injector Pump) but see where you had a pump replaced, I hope it was this one not the Injector Pump.

    I once did a delivery on a boat where the Onan Genset would cut out after a few hours running. The filters etc were always full of air and a bleeding got it going ok again.

    I swapped the supply to the one the main engine pulled from and all was good.

    It was later found that when the boat had been in Spencers having a big refit some SOB had been too lazy to remove a rag from the fuel tank that was getting sucked up to the bottom of the gensets pickup pipe, I am assuming it fell off when the system lost suction which let me prime it up a few times.

    Hopefully you will get it sorted before you blast off on holiday.
  3. C4ENG

    C4ENG Senior Member

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    As an engineer I was being handed over a 150ft yacht a few years back. The engineer leaving told me I had to keep the day tank half full or I would get air locked in all the engines. I asked why and he told me he did not know why but the last engineer told him that and he was telling me the same. As time went on we had a yard period and I was having the tanks cleaned. I climbed in the day tank after being cleaned to see if I could see any reasons as to the warning I received. I inspected the pick up tube very carefully and I could see what looked like a hole half way up/down the tube and then what looked like 2 part epoxy plugging the hole up as a cheap repair. I could see how the engines would had become air locked at one time at half way point in the day tank. But how could there be a hole half way up the pick up like that?
    My best hypothesis... A previous engineer on board was mistreating others while doing a yard period and was upsetting the yard workers. The yard workers had a trick up there sleeves for that kind of a guy and they drilled the 1/2 way hole in the pick up for there revenge and story telling later for that type of engineer they know just how to handle.
    Moral of the story, don't be a %&#$bag! :D
  4. sunchaserv

    sunchaserv Member

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    Some marine gensets have a high temperature cutoff placed so low RW flow will cause a high temperature at that point and shutdown (shut off fuel). This will occur before the different temperature gauge location reads high and gets triggered with potential engine damage. If changing out the "bad" RW impeller cured trhe problem this may be why. Low RW flow shutdown is a common engine shutoff scheme via Borel or other RW flow gauges too, maybe you have one of these hidden in your loop.
  5. dennismc

    dennismc Senior Member

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    When I upgraded and replaced the original gensets 2x20kw, I ran into the same issue, discovered that the new genset fuel pumps were not as strong as the older ones, even though I added a booster pump for ea set, I ended up installing a 30 gallon day tank for the gens. Perfect ever since.
  6. Kafue

    Kafue Senior Member

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    You are right, it was the SW impellor.
    Thanks for the advice. Maybe the fuel has cleaned itself up at the same time co-incedently?
  7. Kafue

    Kafue Senior Member

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    This is the most likely scenario to me and the most "wishful!"
    If there is such a cut off then that would explain why the genset would often shut down within minutes of being started after a long rest (with the usual pre-heat).
    Makes sense. Low water flow=shut off before the heat becomes too high to cause damage.
    Another point, when I went over the manual for the genset, it showed a row of gauges for temp, oil etc. BUT there is no oil pressure or any temp gauge on the genset, just an hour metre
  8. Liberty

    Liberty Senior Member

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    Probably wouldn't hurt to install some gauges but having said that I don't remember seeing any on my last Onan either ...
  9. K1W1

    K1W1 Senior Member

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    Hi,

    This might indeed be the case if the Priming Pump you have referred to in your previous post is a SW Priming pump.

    If it isn't then if the stop signal was given based on a temperatures probes signal the increase in fuel flow by using the priming pump wouldn't change the water flow/temperature.

    If you are actually accumulating air in the fuel try this.

    If you can disconnect the fuel line as close to the tank as possible, connect a vacuum gauge to the end leading to the engine, run the manual pump till you have at least 10" Vac and see how long it holds. It should be rock solid for at least 5 mins.
  10. Kafue

    Kafue Senior Member

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    Mate,
    The priming pump is a fuel pump for the port & stbd engines. As for the rest of your good advice PLEASE do not be offended if I answer with a simple.....if it ain't broke (yet) leave it the hell alone!
    I know you are right but the generator ran all this afternoon and I am over the moon, so I am walking quietly and hoping I get a few *$#@!!! months of PEACE!
    Cheers K1W1, your advice always welcome.
    George
  11. Capt J

    Capt J Senior Member

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    The vast majority of generator shutting down issues I have seen, are a result from either a :dirty fuel filter, bad raw water impellor, or broken belt. (presuming all of the fluids are full).
  12. chesapeake46

    chesapeake46 Senior Member

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    Hi,

    I was able to get a schematic for my genny which has proved to be a great help in troubleshooting this type of stuff.
    If you have the model and serial #'s you might be able to get copies.
    I got mine from a generator service and repair company, not even a marine guy.

    Mine is a 7.5, Onan, 30 yrs old.
  13. Kafue

    Kafue Senior Member

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    Genset back to shutting down

    Hi,
    After changing the impeller, the genset ran faultlessly for the first time in months. That is until I added a fuel additive to clean up the accumulated growth in the mid tank which was obvious when looking at the racors.
    When I added the additive I also put in 100 litres of fuel after so that the fuel hose would not have concentrated additive covering them until the next fill up. This was the mid tank.
    Now, today, I was checking and topping up the many batteries, had the generator running and it kept cutting out. Swapped fuel tanks to the Fwd, same issue.
    I believe that I have introduce air back into the system when I opened the fuel tank to put in additive and fuel.
    K1W1, I spoke with the skipper of the PO and he confirms there has been a "small airleak" for a while. I'd say this is now a bigger air leak that I accidently bled out by changing the impellor.
    I think i should save time and effort=$ and get a new fuel hose from tank manifold to generator.
    Your advice guys?
  14. dennismc

    dennismc Senior Member

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    I suggest you get some clear plastic fuel hose , from the fuel pump to the injector pump, see if you are getting clean, air free fuel to the inj. pump first, then if not, work back from there, ??fuel filters for air leaks etc... if no air in the fuel line, then it's "starvation" of fuel, check also that fuel is returning from the injectors, if not, it;s air or starvation, or bad pump.
  15. Kafue

    Kafue Senior Member

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    Okay, will try this on the weekend, meantime, question:
    Why would it go trouble free after replacing impeller then trouble again once the tank has been opened to air?
  16. karo1776

    karo1776 Senior Member

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    Excellent idea... a piece of clear line... but I prefer a sight gage at a high point in the line (bubbles rise) ... plumbed in... also a pressure gage fitting in the line to the injector pump.

    Dirty fuel:
    Assuming the design of the piping is good and the plumbing is good... dirty, crudy, watery, growth ridden fuel are problems on all boats with large tanks and on and off use suffer this issue. So it is a very good idea to have a pressure gage plumbed across the inlet and outlet of the filter... all filters. At a glance you can tell if you have a dirty filter... and how dirty. All filter manufacturers have pressure drop rating of the filter... paint a red line at the maximum pressure drop across the filter. MANY FILTER MANUFACTURES have some version of this... built in usually a sensor indicator. You need the pressure gage or a sensor and remote gage selector repeater or data acquisition system and computer on any ocean going boat.

    Leakage in line:
    The supply line to the generator fuel pump... or main engine fuel pump should have a pressure gage installed and a red line painted on the minimum supply pressure recommended by the engine manufacturer... This needs to be an absolute gage (does not start zero at atmospheric but at zero pressure) often this has a gage face showing vacuum to pressure. It is overkill but a pressure gage or sensor in the full pump to injection pump line on the generator... some come with a sensor... some don't. On any ocean going boat (offshore) these are vital. If you have a fuel problem you want to know quickly without tapping in with a pressure gage into the line for troubleshooting which is messy and time consuming. These can be sensors with a remote repeater or gage for checking without crawling all over the engine room. The engine manufacturer can give you min and max supply pressure specs... and paint the gage if you cannot remember or don't have a remote sensor system hooked up to a monitoring system computer.

    Problems with the pressure piping from injection pump to injector are rare. I have a piezo electric sensor on board that attaches to a timing light for checking injection timing. This is usually done rarely by the service techs on say a 1000 hrs check... but I insist it is on board any boat I own. This can also be used to check proper function injection pressure by monitoring the output signal strength. The sensor clamps around the piping. This is a little sophisticated for most... but it is how you do it underway. And, you can spot a bad injector.

    Problems with leaks on return lines from the injectors are quite common but not critical just messy. Usually the lines rot (seemingly quicker than anything else).

    I consider these fuel sensor and air-cleaner sensors (across the filter) vital. Big ships have these systems. In my early days as an engineer I worked in the test lab and designed instrumentation and control systems in the lab and on several power plant projects (not boats) we had all kinds of instrumentation... a lot I designed... some of these projects were with new highly developmental diesel engines for both Cat and DD... . Even in that environment these simple steps solve the problem of quickly locating problems. In the test lab we were concerned with gathering data not on playing around with pesky plumbing and supply problems.

    On a boat you should be too.
  17. Capt J

    Capt J Senior Member

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    It sounds like the additive you added, killed the algae and now the generator has clogged fuel filters.
  18. RT46

    RT46 Senior Member

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    my generator would occasionally cut out only when I was running the mains at cruise.

    I found a leak in a plastic fitting above the fuel filter and fix that and it got a little better, but still happened.

    I flipped the racor on the main and it solved the problem. The gague was showing only a slight vacume.

    My generator feeds off the stbd dual racor.

    it seems there was enough restricition on the main filter to starve and shut the generator but not the main.
  19. Kafue

    Kafue Senior Member

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    Just changed the fuel line from the manifold (shared with the port engine) and found it was badly worn BUT unfortunately a new fuel line has made no difference.
    Next step will be to fill a bucket with diesel, drop the new fuel feed line in it and see if it runs.
    Thanks to you all for the input. ****! frustrating.
  20. K1W1

    K1W1 Senior Member

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    Hi,

    Now you have the line dis connected it should be a relatively straight forward deal to use a Vacuum Gauge and see what happens and where.