3hp outboard cooling water flow- normal?

[skyflyer]

I have an ancient 3hp 2-stroke and have just replaced the impeller and given it a start-up and run (without prop) and fairly low revs as its not under any load.

What sort of 'flow' should i expect from the cooling water outlet under these conditions? I am getting a feeble dribble.

Assuming this is a bit on the low side, and that the channels are caked up with years worth of salt, how long do i need to run it in fresh water (maybe with a prop to give load?) to allow salt to dissolve out - or is that a futile hope?

 

[RichardS]

I have an ancient 3hp 2-stroke and have just replaced the impeller and given it a start-up and run (without prop) and fairly low revs as its not under any load.

What sort of 'flow' should i expect from the cooling water outlet under these conditions? I am getting a feeble dribble.

Assuming this is a bit on the low side, and that the channels are caked up with years worth of salt, how long do i need to run it in fresh water (maybe with a prop to give load?) to allow salt to dissolve out - or is that a futile hope?

Are you referring to the tell-tale water outlet or the actual water outlet?

Richard

 

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All three outboards I'v owned have had a healthy stream of cooling water. If the outlet is removable, try taking it off. There may be a blockage there. I once had one blocked by a mollusc. I would have thought that salt is ultimately soluble, it would just take time.

 

[Tranona]

Last month's PBO had an article on this very subject. Used a bigger engine to illustrate, but the principles are the same. Takes a lot to shift deposits in waterways. Just running fresh water through will not make any difference, although of course if done regularly when waterways are clear will reduce build up.

 

[VicS]

I have an ancient 3hp 2-stroke and have just replaced the impeller and given it a start-up and run (without prop) and fairly low revs as its not under any load.

What sort of 'flow' should i expect from the cooling water outlet under these conditions? I am getting a feeble dribble.

Assuming this is a bit on the low side, and that the channels are caked up with years worth of salt, how long do i need to run it in fresh water (maybe with a prop to give load?) to allow salt to dissolve out - or is that a futile hope?

You don't say what outboard ! Make, model and age !

In the majority of cases the cooling water mostly exits underwater with the exhaust gases (Seagulls being the notable exception) where of course you cannot see it.

Most modern outboards have a tell tale from which a fine but fairly strong jet of water issues to show that the pump is pumping OK. In some this only "pees" when the engine is warmed up and the thermostat opens.

In addition there are usually ( always AFAIK) one or more ports or openings on the back of the "leg" from which some exhaust gas blows. Normally a little water is blown out also but it may be only a few spits and spots or just a mist

I assume your engine has a tell tale which is not peeing strongly, just dribling like an old man with a serious prostate problem.
If so check the telltale is clear all the way from the connection at the engine to the outlet.

Also check if the engine is overheating or not. It should be possible to touch and maintain finger contact briefly on any part of the cylinder block and head , except perhaps close to the spark plug. If you cannot then its probably overheating.
If there is any discolouration of the paint it probably indicates over heating.
If a splash of water sizzles and boils it indicates over heating.

Salt may well dissolve and flush out easily but the cooling water passages are more likely to be blocked with an insoluble mixture of limescale and aluminium oxide rather than just salt.

If there is some flow through the engine a chemical clean with an acid descaler or Rydlyme might sort it out but more likely some parts are completely blocked and will require cylinder head off and possibly separation of the cylinder block from the "leg"to clean them out mechanically.


All the water exits from under the block on Seagulls ( except 102 models)

Most modern outboards pee from a telltale like this Evinrude

 

[rob2]

My 2 stroke Tiohatsu 3.5 (also base model for Mariner and Mercury 3.3 models of that era) should pee as in that picture, but is prone to salting up where the rubber hose goes onto the spigot. Inserting a soft wire into the spigot tends to clear it, although it is easier to access if the casings are removed and the rubber hose. If available, an air line applied to the telltale may sufficiently disturb any crud so that it disagregates and flows out with the water.

Rob.

 

[VicS]

My 2 stroke Tiohatsu 3.5 (also base model for Mariner and Mercury 3.3 models of that era) should pee as in that picture, but is prone to salting up where the rubber hose goes onto the spigot. Inserting a soft wire into the spigot tends to clear it, although it is easier to access if the casings are removed and the rubber hose. If available, an air line applied to the telltale may sufficiently disturb any crud so that it disagregates and flows out with the water.

Rob.

The evinrude has a 90 degree elbow/ nipple which the tell tale hose connects to... its plastic so care needed.


and a jet/nozzle in the lower cowl, which restricts the flow, at the end of the hose. This is what gets blocked now and then. Its also plastic and one of the clips has broken off

 

[skyflyer]

That was a fantastic education for me, thanks. I had no idea there were separate outlets and one was a tell tale! (it struck me that it was producing so little water that the cooling effect would be minimal but I did wonder if it had a thermostat. I sort of expected a low power model like this to be pretty simple - in fact I'm surprised its not air-cooled like a mower or chainsaw, of similar horsepower)

This outboard is the 3hp version of the now defunct and little known "Force" brand, which was I think taken over by Mercury/Mariner; it certainly has plenty of parts in common with 2, 2.5 and 3 hp of those alternative makes!

There is a big port on the trailing edge of the leg which obviously is the exhaust port. Above it are two smallish holes and when the leg is lifted out of the water (engine stopped!) these drain quite powerfully for quite a long time - given that I only had the bottom few inches submerged, I think they are doing more than just draining the leg, presumably these are the exit points for the water flow. although I guess it may also go into the exhaust itself?

The outboard is sufficiently old that I would be reluctant to start removing heads and splitting crankcases and so forth as I suspect the stainless nuts are well and truly corroded into the alloy body etc. Frankly it was purchased in a hurry at start of 2015 season for not very much money at all, (about £120) and did me and my 2.3m inflatable tender just fine last year for getting to and from the boat etc. I just thought I'd try and give it a bit of TLC this winter.

In terms of using a limescale remover as suggested above, would you suggest actually trying to run the engine with it as a cooling fluid or by syringing it into the various apertures and flushing later?

 

[RichardS]

That was a fantastic education for me, thanks. I had no idea there were separate outlets and one was a tell tale! (it struck me that it was producing so little water that the cooling effect would be minimal but I did wonder if it had a thermostat. I sort of expected a low power model like this to be pretty simple - in fact I'm surprised its not air-cooled like a mower or chainsaw, of similar horsepower)

This outboard is the 3hp version of the now defunct and little known "Force" brand, which was I think taken over by Mercury/Mariner; it certainly has plenty of parts in common with 2, 2.5 and 3 hp of those alternative makes!

There is a big port on the trailing edge of the leg which obviously is the exhaust port. Above it are two smallish holes and when the leg is lifted out of the water (engine stopped!) these drain quite powerfully for quite a long time - given that I only had the bottom few inches submerged, I think they are doing more than just draining the leg, presumably these are the exit points for the water flow. although I guess it may also go into the exhaust itself?

The outboard is sufficiently old that I would be reluctant to start removing heads and splitting crankcases and so forth as I suspect the stainless nuts are well and truly corroded into the alloy body etc. Frankly it was purchased in a hurry at start of 2015 season for not very much money at all, (about £120) and did me and my 2.3m inflatable tender just fine last year for getting to and from the boat etc. I just thought I'd try and give it a bit of TLC this winter.

In terms of using a limescale remover as suggested above, would you suggest actually trying to run the engine with it as a cooling fluid or by syringing it into the various apertures and flushing later?

The holes which drain out are probably the intake holes. Most of the cooling water will come out with the exhaust and some out of the teltale.

You might be able to remove a plastic constrictor thing on the telltale and check that is not blocked. Then get some limescale remover (HCl, vinegar, lemon juice, even proper stuff) and inject it down the telltale and see if you can get that cleared. Work on the main intakes after that. I have some sulphamic acid at home which is the pukka stuff but other acids also work. If you hear some fizzing it's working!

Richard

 

[skyflyer]

The holes which drain out are probably the intake holes. Most of the cooling water will come out with the exhaust and some out of the teltale.

You might be able to remove a plastic constrictor thing on the telltale and check that is not blocked. Then get some limescale remover (HCl, vinegar, lemon juice, even proper stuff) and inject it down the telltale and see if you can get that cleared. Work on the main intakes after that. I have some sulphamic acid at home which is the pukka stuff but other acids also work. If you hear some fizzing it's working!

Richard

The intakes are in the gear-hub in front of the prop, where the impeller is housed, about 6 small slots in the edge of the casing that houses the impeller. I have now found an online manual http://boatinfo.no/lib/mercury/manuals/22-25-3-33.html#/0 which seems to be the identical model but it gives precious little info about the cooling - i think that section may be missing!

I have previosly used brick cleaner to descale head pipes etc.,which is (i think) HCl or H2SO4 but am a bit wary of whether thats a great idea on the inside of an engine!

I guess the answer is to put the prop back on and find a dustbin to give it a proper run to warm it up and see whether its overheating or not, as I don't think its good to run an engine with no load on it is it?

 

[VicS]

The intakes are in the gear-hub in front of the prop, where the impeller is housed, about 6 small slots in the edge of the casing that houses the impeller. I have now found an online manual http://boatinfo.no/lib/mercury/manuals/22-25-3-33.html#/0 which seems to be the identical model but it gives precious little info about the cooling - i think that section may be missing!

I have previosly used brick cleaner to descale head pipes etc.,which is (i think) HCl or H2SO4 but am a bit wary of whether thats a great idea on the inside of an engine!

I guess the answer is to put the prop back on and find a dustbin to give it a proper run to warm it up and see whether its overheating or not, as I don't think its good to run an engine with no load on it is it?

I would use a sulfamic acid based descaler such as Fernox DS-3 which should available from plumbers merchants. It is a much stronger acid than organic acids like acetic acid but not as strong a for example hydrochloric acid. on which some brick cleaners are based

 

[skyflyer]

Success (I think) - steady stream, from tell-tale, now, putting out about 250cc per minute at just above idle speed

I poked about with a bit of wire through the tell-tale spout and ran it all in a bucket of brick cleaner (diluted) before flushing with clean water.

Hopefully thats done the trick. The cylinder head didn't feel very hot and the water out the tell tale was only slightly warm. Presumably if the main flow was blocked but the tell tale running it would become very hot very quickly!

 

[VicS]

Success (I think) -

Presumably if the main flow was blocked but the tell tale running it would become very hot very quickly!

The engine would show signs of overheating but the telltale may not get particularly hot. I'm not sure quite whereabouts in the cooling system it comes from on that engine, but if its temperature increases suspect a problem

Steam from the exhaust back pressure relief port(s) on the leg is another sign of restricted water flow.

 

[skyflyer]

The tell-tale 'spigot' is on the upper part of the engine cylinder so I assume it is not from the delivery side of the water flow (which would be a bit pointless, not that means they wouldn't design it that way!)

From a practical perspective, this engine is for my inflatable dinghy and it doesn't go anywhere I can't row to or back from if it stops. Having said that I have treated it very gently last year and wouldn't mind giving it a bit more welly this year now/if I know its in GWO!

I see there are all sorts of kits and spares available, so i could rebuild the card, fit new bearings and seals, etc. Only trouble is it would be cheaper to buy a new (second-hand) outboard! I already spent £35 on a new fuel tank as the old one was cracked. Have to keep it all in proportion!