update on my 4hp Yamaha OB and the hot water discharge ...

[old school]

just thought some would be interested in what I've done and if the problem was solved (it wasn't) - my original post from April 15th is below/at the bottom

so I pulled the lower unit (quite easy with the help of a youtube video) and pulled out the cooling impeller ... it didn't look as bad as I thought it would but the dealer was more than happy to sell me a new one

there were some tiny shells and a bit of sand in the housing so I washed that all out and reassembled everything BUT after firing it up the cooling stream was still weak and the water became too hot for my hand SO basically nothing changed (except my wallet is lighter)

I am going to see a friend who said he will blow out the water discharge with air - we are going to blow the air into the small water discharge hole on the bottom of the motor (next step, if needed, would be pulling the lower unit again and blowing the air into the steel tube) - hopefully that will dislodge anything that may be stuck in there

if anyone has any other ideas they would all be appreciated

thank you



ORIGINAL POST
outboard motor discharge water - how hot?

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my 4hp, 1990 yamaha discharges cooling water that is too hot for my hand (not boiling but a wee bit too hot) - stream is not strong

is that normal?

 

[Major Catastrophe]

Original post.

 

[Questor]

I've got exactly the same problem with my Yamaha 8hp outboard. It started to deteriorate after it's first season. I always endeavour to flush with fresh water after use.

Tried the same fixes as you, including a thorough internal cleanout, but no real improvement.

A small allen key wiggled around up the outlet often cures it, although you need to be careful as the water coming out can be very hot.

I know another person with the same motor, and has also got the same problem.

Whether this is typical of just Yamaha motors, I don't know. However, my Yamaha dealer suggested it was a fairly common problem

My suspicions are that the waterways around the head are very small, and tiny pieces of salt / sand are enough to block it, especially around the outlet pipe.

I've put a plastic extension pipe on the outlet, that exits through the transom of the tender, so I can easily see whether water is flowing - bit like a metre long rooster tail, although a permanent fix, if anyone knows of one, would be preferable.

 

[Cliveshep]

I'd be tempted in your situation I think to pull the head off and make sure everything was clear and clean.

Also - does it have a thermostat, it's possible this is either faulty or there is crud in the housing restricting any flow when it does open.

There just has to be a logical reason and you just have to find it!

I have heard of various ways to clear without stripping, one poster used boiling water, another used a load of Tesco's vinegar and yet another used Fernox, all in the test tank I stress. The proponents of all three methods announced their success with their methods.

Fernox here: http://www.fernox.com/home

 

[old school]

another update and thank you

1st, thank you for the suggestions

today I did the "almost" boiling hot water - twice

after the 1st time the discharge water was dramatically cooler (just warm to hot) - but after the 2nd time it got hotter again - leads to me believe that there may be a small shell or small obstacle that is stuck somewhere in the cooling tubes and is changing positions (much like a carburetor choke)

tomorrow I am going to take it to my friends garage and have him blast the small discharge hole

 

[AndieMac]

Has the little motor been started dry, out of the water at any stage?

Sometimes the inner SS surface of the water pump housing can score/distort from the heat of dry rubber (impeller) against the liner, and its not always easy to detect to the untrained eye. It doesn't need much scoring to lower the efficiency of the impeller.

Drop the lower case again and show the pump housing to a techie for a quick appraisal.

 

[[2068]]

tomorrow I am going to take it to my friends garage and have him blast the small discharge hole

Bear in mind the small discharge hole is the telltale, not the actual outlet. There should be lots of water circulating around the head, 99% of which will leave via the pipe into the exhaust, and a tiny amount from the small discharge hole.

On my Merc 5hp, the hole had become smaller thru corrosion, so I made it a bit bigger again and repainted, but this had nothing to do with the cooling water temp.

 

[PaulGooch]

<snip>

tomorrow I am going to take it to my friends garage and have him blast the small discharge hole

In all honesty, this will be a waste of time.

Firstly, as pointed out by FlowerPower, the small hole is only a tell-tale. It's there so you can see the pump is working. If this hole was 100% blocked the engine should still run at normal operating temperature. By all mean clean it out so you can see the tell-tale squirt of water though.

Secondly, if there is any kind of obstruction in the system, air from a garage airline is unlikely to shift it. The air would more likely just go around it. Unless of course you used a massive amount of air, which most garage airlines cannot deliver. If you suspect a blockage you would be far better connecting a hose to the flush adaptor and flushing the engine through. Connect it to the highest volume water supply you have access to and leave it for a good while.

 

[mitchc]

Been watching this post with interest as I have a yammy 8hp 2stroke that has the the same symptoms.
Although I agree the tell tale is only an indication that water is circulating, it should be at the same temp as the water flowing round the engine. I found that the tell tale got blocked very easily, best thing to unblock is a length of solder.....if this doesn't improve the temp of tell tale then try the following:
On the 8hp there is a exhaust plate on the side of the side of the block. I removed this and found that on the initial build of the engine an excessive ammount of RTV (sealant) had been used and was partially blocking some of the coolant passages. I cleaned this away and refitted, tell tale was much cooler hopefully indicating the flow round the engine was better. I also removed the t/stat and found that even after only one seasons use is was pretty manky. Again cleaned this and it's housing and the temp was much better.

You can get schematics and parts info here:
http://www.yamaha-motor.com/outboard/parts/home.aspx

I'd say a very hot tell tale is an issue....it indicates the temp of the cooling water around the engine and you need to get to the bottom of the problem. I've found that the water pump housing and impellor are pretty robust, and my thoughts would be that if you have a weak tell tale it's more than likely that you have find a way of cleaning out the coolant passages in the engine...do a search on the forum for lots of techniques.
I'd recommend this stuff though:
http://rydlymemarine.co.uk/ available from chandlers and the like....

Good luck.

 

[old school]

now I get it

thank you for everyone's patience ... I didn't waste my time on blowing air into the tell-tale.

I am going to try and pick up some "water-muffs/ears" and run the motor with lots of water thru it (only been running in a bucket so far - also may try the "dissolvent" in the bucket next to see if that helps).

Hope I am at least providing some "newbee" humor to everyone who has already worked on motors. I will keep at it.

By the way - BIG thanks for the Yamaha parts link - I have been trying to find that link and all I ever got were shops wanting to sell me manuals.

 

[old school]

hooking up to BIG water supply didn't work but ...

I did find out (thru helpful schematics) that it does indeed have a thermostat which I have purchased and will be installing

QUESTION - the shop would have to order the 2 exhaust head gaskets - do I need them or are they pretty hardy and can survive a thermostat replacement AND does anyone know if those exhaust plate bolts need to be tightened precisely with a "torque wrench"? (numbers 28/29/30)

That schematic was super helpful - thanks again!

 

[mitchc]

QUESTION - the shop would have to order the 2 exhaust head gaskets - do I need them or are they pretty hardy and can survive a thermostat replacement AND does anyone know if those exhaust plate bolts need to be tightened precisely with a "torque wrench"? (numbers 28/29/30)

Morning Old School,
I've re-used the gaskets on my 8hp a couple of times now and not had any problem...my advice though is for how much they cost get them cause you won't really know until you take off the covers. Makes sure you clean the sealing surfaces of the plates before you re-fit.
With regards to the torque wrench, it depends how well calibrated your wrist is. I've built hundreds of engines so find on that kind of bolt I dont need a wrench, but if you are not sure it's best to use one. A stripped thread will be a real pain in the butt!

I found on my 8hp the tell tale gets blocked and disturbed very easily by bit's of scale inside the engine, then when it finally clears it does feel very hot. I've now got a length of solder wrapped round the handle that I use if the t/tale gets blocked.

Try filling the water jacket up with vinegar to clean out some of the deposits.....good luck, anything you do to clean it out will show some improvement.

 

[old school]

thanks mitch

i will give it a go!

 

[ian38_39]

I have an 8hp Yamaha and suffer from high temp tell tale at low revs, as soon as the engine is given a bit more the tell tale cools down.

My particular engine was picked up for £80 and is a 79 vintage, for that reason I didn't fancy spending money on it so it was a case of running it till it breaks, 2 years on apart from having to start it by wrapping a cord around the emergency start after the recoiler broke (parts no longer available so if someone has one off an old engine they want to sell) it is still running fine.

Maybe high temps on a Yamaha 2 stroke are not such a problem?

 

[old school]

conclusion 4hp over-heating

after trying to avoid pulling off the exhaust plates and checking the thermostat (OK, after i had a couple pints) - i pulled the two plates and found all channels and the thermostat caked in sand and small bits of shell

cleaned everything out, cleaned and scraped the thermostat and tested in boiling water several times (it works fine)

since the exhaust port (and cylinder) can get sea water in it easily if a gasket is torn or weak, i decided not to risk it and ordered 2 new gaskets

shoudl be in next week and i fully expect to have a strong cool stream (the engine, not me)

thank you everyone for your advice


ps - instead of just pulling the on/off gas lever off/out of the built in tank i tried to unscrew the brass lock nut on the gas petcock - bad idea as it snapped the metal alloy petcock (when something has not been unscrewed in 20 years - oh well) - i repaired that with JB WELD (cold weld epoxy and it worked great - and much cheaper than a new petcock)