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  1. #1
    Join Date
    Apr 2019
    Posts
    16

    Default Overheating outboard - most likely salt build up

    We got into a bit of a fix today, when the 5hp Yamaha outboard on our sailboat decided to overheat and cut out. At least we are assuming thatís what it was. It would loose power and stop. Trying to start it immediately it would not run in gear or much above tick over. Leaving it sit for a while allowed it to run longer, but even going as gentle as possible it would eventually lose power and stop.

    Weíve only had the boat and engine for five months so do not know the history of the engine, a Yamaha 5cmh 2-stroke.

    Iíve never been enamoured by the flow of cooling water out of the engine, unlike our new Mariner 3.5 dinghy motor which positively pi$$es out in comparison. That, and it did feel warmer than I would have expectedly. The Yamaha is a bit too large to offload and bring back to flush thru after each outing unlike the dinghy engine which gets flushed every trip.

    Two weeks ago, it had a fuel problem, before then it had been perfect. I replaced the pump diaphragm which was stretched as well as finding a little metal button detached from it and floating around the pump chamber.

    I also took the opportunity to replace the impeller and found the waterways just below it solid with salt.

    On reassembly it ran sweeter than ever, started with half a pull but not much improvement in the water flow. I presumed that maybe itís just the way it is. Especially after using it all last week taking us on and off moorings and then this morning we used it for a good hour I guess (longest run ever) to get us out into some wind, we never run it hard, and it never missed a beat, until we needed it this evening on the way back.

    Only positive is that anyone watching us return to the mooring and picking it up under sail might, just for one moment, have thought we might know what we were doing (fools!)

    So, now you know the background, before I strip the engine down is there any magic solution that I can use to flush thru the engine in a wheelie bin that might do the trick at dissolving any build up?

    Chris

    PS sorry for the war and peace, but wanted to give all information.
    Last edited by chris-s; 25-08-19 at 18:47.

  2. #2
    Join Date
    Sep 2011
    Location
    west midlands
    Posts
    1,033

    Default Re: Overheating outboard - most likely salt build up

    Quote Originally Posted by chris-s View Post
    We got into a bit of a fix today, when the 5hp Yamaha outboard on our sailboat decided to overheat and cut out. At least we are assuming that’s what it was. It would loose power and stop. Trying to start it immediately it would not run in gear or much above tick over. Leaving it sit for a while allowed it to run longer, but even going as gentle as possible it would eventually lose power and stop.

    We’ve only had the boat and engine for five months so do not know the history of the engine, a Yamaha 5cmh 2-stroke.

    I’ve never been enamoured by the flow of cooling water out of the engine, unlike our new Mariner 3.5 dinghy motor which positively pi$$es out in comparison. That, and it did feel warmer than I would have expectedly. The Yamaha is a bit too large to offload and bring back to flush thru after each outing unlike the dinghy engine which gets flushed every trip.

    Two weeks ago, it had a fuel problem, before then it had been perfect. I replaced the pump diaphragm which was stretched as well as finding a little metal button detached from it and floating around the pump chamber.

    I also took the opportunity to replace the impeller and found the waterways just below it solid with salt.

    On reassembly it ran sweeter than ever, started with half a pull but not much improvement in the water flow. I presumed that maybe it’s just the way it is. Especially after using it all last week taking us on and off moorings and then this morning we used it for a good hour I guess (longest run ever) to get us out into some wind, we never run it hard, and it never missed a beat, until we needed it this evening on the way back.

    Only positive is that anyone watching us return to the mooring and picking it up under sail might, just for one moment, have thought we might know what we were doing (fools!)

    So, now you know the background, before I strip the engine down is there any magic solution that I can use to flush thru the engine in a wheelie bin that might do the trick at dissolving any build up?

    Chris

    PS sorry for the war and peace, but wanted to give all information.
    If you have flow...albeit small you have a chance. You can buy outboard flush that I have used in the past to good effect.

    Not the one I used but would do the trick....

    https://boatworld.co.uk/blu-thru-boa...BoCQtMQAvD_BwE

  3. #3
    Join Date
    Jul 2018
    Location
    Bewdley, Worcs
    Posts
    459

    Default Re: Overheating outboard - most likely salt build up

    Your problem sounds to me more like fuel starvation to be honest, but you may have a corrosion buildup in the engine as well which isn't helping.

    There is an awful lot of complete crap talked about the area beneath the impellor, including many YouTube idiots producing well-meaning but completely wrong vidoes showing you how salt builds up in the area beneath the impellor and how to clean it and how cleaning it is important.

    It isn't.

    The area under that metal plate fills up with salt because water is basically not moving in that part. That area is NOT part of the water path. Water enters the impellor through that hole in the plate, and the water comes from a hole directly underneath that hole in the plat. The curved track that fills with salt is behind that area, and has absolutely no effect on water flow, its just a part of the casting that can be totally ignored.

    Your engine *may* have corrosion buildup that you can clear with either hydrochloric or phosphoric acid, easy to do, I have rescued more than one engine that was declared "beyond hope" by a professional.

    I use "brick and patio cleaner", which is basically hydrochloric acid. I remove the gearbox and use a garden sprayer to pump it up the brass feed pipe into the engine, slowly. I do this for about an hour, leaing it to fizz and bubble occasionally. Hydrochloric WILL eat aluminium eventually, so wash ti through afterwards. It eats the corrosion far faster than it eats the ally, so nothing to worry about.

    Iíve never been enamoured by the flow of cooling water out of the engine, unlike our new Mariner 3.5 dinghy motor which positively pi$$es out in comparison.
    Don't comfuse the amout of water coming through the tell-tale with the flow of water through the engine ... only a tiny percent of the colling water comes out through that tell-tale --- 99% coes out and down the exhuast leg. Although your Mariner pees it out, that is the amount in the tell-tale, not the flow in the engine, the Yamaha may still be shifting a LOT of water, just at a lower pressure and with a smaller tell-tale.
    Last edited by rszemeti; 25-08-19 at 21:00.

  4. #4
    Join Date
    Apr 2019
    Posts
    16

    Default Re: Overheating outboard - most likely salt build up

    Thanks for the reply, especially your comments on 'salted up waterways' and the 'telltale'.

    Thinking about it overnight, I think you are probably correct in it being a fuel problem. Loss of power thru overheating would be a sign of seizing, and I don't think that was the case as I was easily able to turn-it-over on the pull cord immediately, the telltale water was not 'hot' and there were no other signs that I would have attributed to running excessively hot.

    Over coffee this morning, I looked back over the fuel pump parts assembly and notice that there is a small diaphragm spring that I don't recall seeing when I replaced the diaphragms. On top of the spring sits a small 'button', this was just floating around and I had assumed it was previously attached to the old diaphragm and so it got discarded, (goodness knows where the spring was) and finally there was an additional gasket that must have been so attached to the old diaphragm I didn't notice, and so didn't replace.

    Geez, what a lousy job I did! How it worked all week I don't know! Fortunately, my marine engineer son, is in Greece so need never know.

    Thanks

    Chris

  5. #5
    Join Date
    Sep 2001
    Location
    Nr Falmouth, Cornwall.
    Posts
    1,484

    Default Re: Overheating outboard - most likely salt build up

    Re the telltale. I have two Yamaha 2 strokes, a 5 and a 6. Both telltales sometimes salt up and Iíve found the easiest fix is to rod them through with a plastic straw of the type you often find attached to aerosol lubrication sprays. Worth a try!

  6. #6
    Join Date
    Feb 2006
    Location
    River Dart
    Posts
    1,527

    Default Re: Overheating outboard - most likely salt build up

    If it’s any use, I flush my Yam15 using a pressure sprayer. We’re too far from a fresh-water tap, so I simply took off the spray wand from a 5 litre spray bottle and fitted a short length of garden hose with a female watering attachment at the end. When we come back into the pontoon, I fill the spray bottle from the hose and attach it to the flush-through point on the engine, pressurise the spray can and let it go into the cooling channels. Flushes the salt away very effectively.

    If you haven’t got a flushing point on the engine, then you could do the same arrangement but with some flushing muffs instead.

  7. #7
    Join Date
    Jul 2002
    Location
    Home: Kent. Boat: Chichester
    Posts
    43,553

    Default Re: Overheating outboard - most likely salt build up

    Quote Originally Posted by rszemeti View Post
    Your problem sounds to me more like fuel starvation to be honest, but you may have a corrosion buildup in the engine as well which isn't helping.

    There is an awful lot of complete crap talked about the area beneath the impellor, including many YouTube idiots producing well-meaning but completely wrong vidoes showing you how salt builds up in the area beneath the impellor and how to clean it and how cleaning it is important.

    It isn't.

    The area under that metal plate fills up with salt because water is basically not moving in that part. That area is NOT part of the water path. Water enters the impellor through that hole in the plate, and the water comes from a hole directly underneath that hole in the plat. The curved track that fills with salt is behind that area, and has absolutely no effect on water flow, its just a part of the casting that can be totally ignored.

    Your engine *may* have corrosion buildup that you can clear with either hydrochloric or phosphoric acid, easy to do, I have rescued more than one engine that was declared "beyond hope" by a professional.


    I use "brick and patio cleaner", which is basically hydrochloric acid. I remove the gearbox and use a garden sprayer to pump it up the brass feed pipe into the engine, slowly. I do this for about an hour, leaing it to fizz and bubble occasionally. Hydrochloric WILL eat aluminium eventually, so wash ti through afterwards. It eats the corrosion far faster than it eats the ally, so nothing to worry about.



    Don't comfuse the amout of water coming through the tell-tale with the flow of water through the engine ... only a tiny percent of the colling water comes out through that tell-tale --- 99% coes out and down the exhuast leg. Although your Mariner pees it out, that is the amount in the tell-tale, not the flow in the engine, the Yamaha may still be shifting a LOT of water, just at a lower pressure and with a smaller tell-tale.
    Not all brick cleaners are hydrochloric acid based . ..................... Read the label and/ or the safety data sheet
    Last edited by VicS; 26-08-19 at 13:45.

  8. #8
    Join Date
    Jul 2018
    Location
    Bewdley, Worcs
    Posts
    459

    Default Re: Overheating outboard - most likely salt build up

    Quote Originally Posted by VicS View Post
    Not all brick cleaners are hydrochloric acid based . ..................... Read the label and/ or the safety data sheet
    What is required is somethign that eats the calcification and crud in the waterways, whilst not attacking the ally too severly. Any brick cleaner is going to be an acid that will attack calcium deposits, or it would not work on mortar. So you may be right that there are brick cleaners that are not hydrochloric based, however I have never come across one, and if there are, they would still work fine for decalcifying an engine.

    Phosphoric is a better choice as is dissolution rate of aluminium in phosphoric acid is lower than aluminum in hydrochloric, but phosphoric is not as cheap or easy to get hold of in bulk. If you know of a good, cheap source of strong phosphoric, that may be of interest.

  9. #9
    Join Date
    Apr 2019
    Posts
    16

    Default Re: Overheating outboard - most likely salt build up

    Thanks again for the ideas.

    After getting the engine back home this afternoon, the first thing I noticed is that the fuel pump cover bolts are all about half a turn too loose! Regardless of missing bits, this would certainly have leaked vacuum and/or fuel and prevented full pressure. Earlier in the day I had noticed the engine smelt a little more petrolly than normal.

    Cheers!

    Chris

  10. #10
    Join Date
    May 2008
    Location
    Scotland
    Posts
    2,080

    Default Re: Overheating outboard - most likely salt build up

    Quote Originally Posted by rszemeti View Post
    What is required is somethign that eats the calcification and crud in the waterways, whilst not attacking the ally too severly. Any brick cleaner is going to be an acid that will attack calcium deposits, or it would not work on mortar. So you may be right that there are brick cleaners that are not hydrochloric based, however I have never come across one, and if there are, they would still work fine for decalcifying an engine.

    Phosphoric is a better choice as is dissolution rate of aluminium in phosphoric acid is lower than aluminum in hydrochloric, but phosphoric is not as cheap or easy to get hold of in bulk. If you know of a good, cheap source of strong phosphoric, that may be of interest.
    Or buy cheap bulk vinegar and run that through the engine until it warms (in a bucket!) Once it's warmed up it is effective at removing calcareous deposits, though it is nowhere near as aggressive as HCl based cleaners.

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