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  1. #1
    Join Date
    Apr 2005

    Default 4hp outboard 2 stroke cleaning blocked telltale water passages

    I posted needing help, I thought I had a mix problem, may still have but:-

    I thought the tell-tale was Ok when onboard, until I fired it up in a dustbin last week.
    The engine runs in a well on the boat but I could hardly see the telltale output and thought it was ok because it was the last time I took it home, a few moths earlier.

    So now, with a trickle, do I change the impeller or is the water passage blocked ?
    The engine has had little use, 20-30hrs since new, but never been flushed.
    The pee pipe is only about 1mm so I feared the thing was blocked.
    After a lot of research on the net and expensive salt remover ideas I came up with this one.

    A tub of hot (not boiling) water, I ran it in this for a few minutes, at higher revs the telltale definately increased, so I thought the impeller must still be ok.

    Didn't run it for more than 3-5 minutes as I think my bucket wasn't deep enough to run properly and didn't want it to overhaet with hot water. I stopped it, put it back in the dustbin of cold water, now the tell-tale is as new. Have ran it from cold several times today in cold water, and it's as fast on startup as when hot.

    Incidentally, I think there is no thermostat on Mercury Mariner 4hp sail motor 2007, the telltale is as fast cold as warm, I now know.

    I was too coward to strip it down and replace the impeller, some articles said do it in forward gear, some said in reverse, and I didn't want to ruin a £700 engine.

    I will bring it home and flush every time now, and have learnt my lesson.

    Thank you all for your thoughts.
    1 more thought, I did wonder whether to put some building or sharp sand in the water, to really give it a good clean, I guess sand in the sea does the same job.
    Any thoughts on that would be interesting.

    I hope this info helps someone out in future.

    Sorry if I wasted anyone's time, but I did discover this so I thought I would share it.


  2. #2
    Join Date
    Mar 2006
    The island of Alderney


    I would recommend against using sand for flushing, if there is a small blockage the sand will get stuck and be tricky to shift.

    As you have found flushing an engine with fresh water is the easiest single way to improve it's life.

  3. #3
    Join Date
    Jul 2002
    Home: Kent. Boat: Chichester


    First thing its always worth doing if the pee stream is weak is to make sure the outlet and the hose are not blocked.

    I sounds as though yours was blocked with salt and that the hot water treatment dissolved it OK. Regular flushing should keep it clear. ( It may only have been the telltale blocked which would not have affected the cooling )

    As far as I can see you are right there is no thermostat on that model. Even where there is a thermostat I would not expect to see much difference in flow from a tell tale hot or cold. They are just an indication that the pump is pumping.

    Don't run it with sand in the water. Not only do you risk blocking the cooling system but it will cause excessive wear of the water pump!

    I see no problems replacing the impeller.

    There is a joint in the gear shift rod accessible via the rubber plug in the lower part of the drive shaft housing. I don't think it will make any difference if forward neutral or reverse is selected but it will be important that the two sections of the shift rod are reconnected in the same relative position to each other on reassembly.
    Only two bolts hold the gearcase on I think. As it is dropped the drive shaft should pull from the crankshaft and the water tube from the pump.
    The bottom section of the shift rod will come away with it leaving the top section still attached to the gear lever.

    Once separated the water pump will unbolt and slide up the drive shaft ... watch out for the impeller drive key.. leaving the shaft in place.

  4. #4
    Join Date
    Aug 2009

    Default Did mine yesterday

    I had a similar problem with a similar motor (5hp 4stroke). I followed the advice on this video:

    Youtube Video

    Reverse gear was better for me, as it lined up the clamp with the access hole nicely. As long as the lever & gearbox both remain in the same gear, it doesn't really matter where you put the clamp back on..obviously, directly beside the hole is best

    2 bolts on the bottom of the leg were all that held it on (13mm & 10mm, I think). 4 12mm bolts hold the pump cover on, the drive pin was just resting on a flat on the shaft, watch out that it doesn't roll away......

    The only problem was getting it all back together, the clamp was an awkward bugger, I solved it with a 'pickled onion grabber' type pickup tool to hold it in place.

    When I saw the old impeller, I thought I had wasted my time. It was intact although 2 blades had taken a permanent set, however the new one has made a significant difference.

    When I ran the engine up in a dustbin, the water from the telltale fluctuated a lot, I presume the improved water flow was dislodging scale that then blocked the telltale hole. 10 minutes of running & poking with a piece of wire resulted in a telltale that squirts out rather than just dribbles.

    Hope this helps.

  5. #5
    Join Date
    Jul 2007


    i just had some problem on yahama 4hp 4 stroke, ended up putting in a bin with £10 worth of vinegar from tescos (think that was about 10 litres worth) and topped up with water.

    Ran it on and off in the bin for about 10mins at a time a couple of times a day for 2 days....seems to have cleaned it out...

    obviously then flushed with fresh water for a good 20mins afterwards.

  6. #6
    Join Date
    Feb 2002
    Home:Nottinghamshire Boat: Blackwater Marina, Essex


    One thing I'd recommend (esp with a 2 stroke which can be turned upside down without any problems) is to fill the waterways with soluble oil when you winterise the engine. This will prevent any out of season corrosion, and will mix with water and flush out when you run again in water at the start of the season.

    With my Suzuki 4hp - I was able to introduce soluble oil through the flushing adaptor inlet using a small funnel.

  7. #7
    Join Date
    Nov 2009


    Hot water and sand! You certainly have some dodgy ideas - hot water will reduce water flow / pressure because it will soften the plastic impellor and sand is likely to block the system even further when the telltale could already be part blocked.

    Personally I wouldnt worry too much about the telltale - its only there to tell you that water is being pumped round the system and it could be totally blocked without there being a real problem. So my inclination would be to poke some softish wire up the hole from the outside and see if this improved things. If it didnt then maybe re-assure myself by stripping and checking the impellor.

  8. #8
    Join Date
    Oct 2001
    Hemel Hempstead UK


    Turning a 2 stroke upside down if there is any water left in the cooling ways can result in water entering the crankcase via the exhaust. It has happend to me and I had to fit new main bearings after the water had rusted the original bearings

  9. #9
    Join Date
    Nov 2009
    County Down, NI


    I was told to poke a piece of lawnmower strimmer cable into my tell-tale as it was more than likely blocked by salt. It was! Certainly worth trying first.



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