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  1. #1
    Join Date
    Sep 2010
    Location
    St Albans - boat at Woodbridge
    Posts
    165

    Default Beta marine 20hp - overheating ideas please

    A bit of history as it might be relevant.
    The engine is 4 years old - 120 hrs on the clock - no previous history of overheating -
    Until last year when the boat was taken out by my son who didn't notice no cooling water coming from the exhaust.
    The engine overheated a few times and destroyed the impeller and exhaust waterlock etc.
    So end of last season, new waterlock, impeller, remnants of antifreeze drained and replaced.
    It ran with no problems for a dozen hours or so before lay up.

    This year, I drained the anti freeze again and put in fresh.
    I cleaned out the heat exchanger (not much in it anyway)
    Last week I had gone approx 1hr when the overheat alarm sounded
    ~Got towed back to mooring and started engine.
    After 30 seconds the alarm went off.
    The boatyard then installed a new thermostat thinking it probably wasn't working.
    I also checked the heat exchanger was clean.

    This morning the alarm went of after 20mins running on my mooring! Engine cover off so no ambient heat.
    There is lots of raw water coming from the exhaust (I measured in a bucket) It wasn't warm but then I'm not sure it should be.
    The heat exchanger felt cool
    The thermostat housing was hot
    The flexible hose that connects to the bottom of the fresh water pump was cold (is that right?)
    I can only think it may be the fresh water pump - but these are very reliable (or are they)

    I will contact beta tomorrow but I'm running out of ideas.
    Do you have any?
    Thanks
    Keith

  2. #2
    Join Date
    May 2013
    Location
    Kirkcaldy, Fife
    Posts
    2,217

    Default

    Do you have an accurate thermometer or are you just going on the alarm? If so you may have a dodgy alarm. It is not uncommon for thermocouples to play up after they have been roasted. Can you squeeze the pump hoses ? If you can there is probably no flow or at least you should feel flow. Never mind the teperature of the cooler, you want to see if there is a temperature difference between the inlet and outlet. I'm surprised that the boat yard changed the thermostat on a suspicion as it can be easily tested in a saucepan of boiling water which would tell you for sure. If you can find or borrow a laser thermometer it will be very simple to see if the engine is running fine and the cooling system working. If that is the case the sensor is knackered.

  3. #3
    Join Date
    May 2001
    Location
    North Wales, sailing Aegean Sea or Menai Strait
    Posts
    21,478

    Default

    I think your diagnosis is correct. Clearly no circulation. Could be the pump impeller, but could also be a blockage, maybe the thermostat for a second time? I would try running without the thermostat, see if the hose and heat exchanger warm up. You can check thermostats easily in a pan of water on the stove. I am assuming you are sure there are no airlocks.

    Unfortunately, and maybe following on from the abuse the engine suffered, cracks in the head can also disrupt circulation. But check the easy things first.
    Answers to some technical queries at new website http://coxeng.co.uk

  4. #4
    Join Date
    Sep 2010
    Location
    St Albans - boat at Woodbridge
    Posts
    165

    Default

    I'm not entirely sure there are no airlocks - but dont know how to check?

    I think a thermometer is a good idea - at least I'll then know what is properly hot and what not!

    PLease not a crack in the head!

    A few more things to look at anyway
    Thanks

  5. #5
    Join Date
    Sep 2010
    Location
    St Albans - boat at Woodbridge
    Posts
    165

    Default

    I now have a new temperature sensor but not sure where it goes.
    I assume its a simple disconnect the wire, unbolt the old and pop in the new one.

    Can someone point me in the right direction to find its location on the engine?

    Many thanks

  6. #6
    Join Date
    May 2001
    Location
    Norfolk/Suffolk
    Posts
    2,875

    Default

    Go to the beta website and download the manual for the BD722, I assume.
    Check antifreeze mixture is correct and raw water inlet is not partially blocked or inlet suction hose is not collapsing under suction. Cure for my Beta problem was larger dia. raw water skin fitting. Clean out thermostat housing and surrounding pipe with bendy wire.
    Harwich for the Continent - Brexit For the Incontinent . Sadler 290

  7. #7
    Join Date
    Jun 2006
    Location
    South East Coast - United Kingdom
    Posts
    7,078

    Default

    Quote Originally Posted by Oldgeezer View Post
    I now have a new temperature sensor but not sure where it goes.
    I assume its a simple disconnect the wire, unbolt the old and pop in the new one.

    Can someone point me in the right direction to find its location on the engine?

    Many thanks
    Go to the back of the temperature gauge on your boat and look at the wiring on the back of the temperature gauge.

    Discount any wiring that is used for illumination and note the colour code of the wire which goes into the back of the gauge from the engine sensor. It could possibly be Green with a Black trace or white with a green trace or something similar.

    Now look on your engine and near the top and close to the thermostat / water pump area you should find a similar coloured wire. Follow it to where it is clipped/plugged into the NTC temperature sender unit. In this way, you should be able to make sure you are on the temperature and not any oil sender unit.



    .
    regards David - DSW Marine Engineering
    www.dswmarineengineering.com

  8. #8
    Join Date
    Dec 2008
    Location
    Sweden
    Posts
    1,464

    Default

    The temp sensor is on top of the engine, to the rear of the injectors, not far from the air filter housing (assuming this has not been changed since the Beta 722, 2005 model)

  9. #9
    Join Date
    Jul 2008
    Posts
    496

    Default

    A bit of history as it might be relevant.

    It will be, especially when you find the cause, look back and say 'Ah yes, of course'.....!!

    The engine is 4 years old - 120 hrs on the clock - no previous history of overheating -


    120hrs - I wouldn't have thought that's enough time to build up any significant scale or other deposits

    Until last year when the boat was taken out by my son who didn't notice no cooling water coming from the exhaust.


    Do you mean "he didn't notice that there was no cooling water..." or " He didn't notice whether there was no cooling water"?

    The engine overheated a few times and destroyed the impeller and exhaust waterlock etc.


    Probably the first then?

    So end of last season, new waterlock, impeller, remnants of antifreeze drained and replaced.


    Remnants? Was there very little secondary cooling water?

    It ran with no problems for a dozen hours or so before lay up.

    Thinking about events so far, then: At some point there was no cooling water emerging from the exhaust. So there was a problem with the raw water (primary) flow. You say the engine overheated a few times and destroyed the impellor.... can I suggest that it was the other way round? That the impellor shredded, the primary circuit failed so there was no cooling available to the engine, which then overheated and damaged the waterlock (V.hot exhaust as no elbow cooling). You then replaced the impellor, secondary water/antifreeze and the engine operated correctly for 12 hours. It appeared to be ok. So what happened between then and this:

    This year, I drained the anti freeze again and put in fresh.
    I cleaned out the heat exchanger (not much in it anyway)
    Last week I had gone approx 1hr when the overheat alarm sounded

    ~Got towed back to mooring and started engine.
    After 30 seconds the alarm went off.
    The boatyard then installed a new thermostat thinking it probably wasn't working.
    I also checked the heat exchanger was clean.


    A thermostat failure could account for the problem but assuming it was working and fitted correctly you have eliminated that.
    I think the heat exchanger is a dead end. The fault occurs at idle (when less heat needs to be dumped) and it would need to be very blocked to be unable to transfer a small amount of heat. You've cleaned it once (I assume you didn't find loads of constrictng sediment/rust/crisp packets) so it should be fine.



    This morning the alarm went of after 20mins running on my mooring! Engine cover off so no ambient heat.
    There is lots of raw water coming from the exhaust (I measured in a bucket) It wasn't warm but then I'm not sure it should be.


    You have plenty of raw water from the exhaust - but it isn't warm. This needs more checking I think. There should be a marked difference between the in and out water. After all, this (apart from background air cooling and exhaust gases) is where the engine heat goes.

    The heat exchanger felt cool
    The thermostat housing was hot
    The flexible hose that connects to the bottom of the fresh water pump was cold (is that right?)
    I can only think it may be the fresh water pump - but these are very reliable (or are they)


    The heat exchanger won't be very hot usually - the raw water flow is taking the heat away. But cool...? And the thermostat housing hot...? It would probably be worth verifying the secondary water circulation now. Reliable or not, everything can fail.

    I don't know how helpful Beta Marine are to end users but it might be worth emailing them. They could give you some 'empirical' tests which don't rely on instrumentation.

    Sorry if others have posted already - it takes me ages to type this stuff!

  10. #10
    Join Date
    Sep 2010
    Location
    St Albans - boat at Woodbridge
    Posts
    165

    Default

    Wow - What excellent help!
    Many thanks to all.

    Concentrik - your analysis looks spot on. The initial cause was raw water intake blocked.
    Will try the new temperature sender today and taking an infrared thermometer with me too.
    I do recall when emptying the fresh water the drainage tap was blocked and I had to poke it with a stick!
    Perhaps something was dislodged.
    I'll report back later today - hopefully the sender was faulty. but...

    Again, many thanks to all.

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