Water uptake.

[57paulimo]

Thanks for the reply Jon.
Today. Removed water jacket and cylinder head, removed exhaust covers (a bit too easy, Davie Anderson said I may have to keep heating up the engine to get some of these M6 bolts out).
Checked all waterways with a squirt of plain water to check for blockages, even the tiny holes going into the left side of the cylinders, everything seems fine.
The one thing I'm struggling to do is to connect a chuck to the drive spline, I haven't got a large enough chuck!
I turned the engine by hand, and the three pistons are doing what they should.
One thing I noticed is an aperture (not a hole) which could possibly be a small crack leading from the lower left jacket to the exhaust cooling jacket??
I'm going to connect the hose to the water uptake and try to block the water inlet to the exhaust manifold, which might tell me if the uptake pipe is perforated.
Before dismantling the engine started quite easily and ran well, then the tell tail got so hot it was steaming, the overheat alarm went off, and I turned it off.
I am at the end of my knowledge now, very perplexed and ready to get rid of the engine

[TmMorris]

It's just osd that the telltale is getting that hot and so quickly. If you had a lean tube doing the overheating for example, it would take time and wouldn't be likely to get that hot.

The only thing generating that much heat, that quickly is obviously the engine doing what it does, being a heat engine.

Have you got a diagram showing where the telltale is in the line of plumbing?

A crack would explain things though.

[57paulimo]

Guys, can anyone tell me what would be the outcome of me putting too much oil into the petrol?
When I had the waterways cleaned of salt and crude, the guy convinced me to ditch the auto lube and to add oil to my fuel each fill up.
I really, really hope I haven't added way too much oil to the fuel I've been using..........

[Oldman2]

Use a 1/4 or 3/8" drive and a suitable socket that fits snugly over the drive rod, gaffer tape it on and grip the other end of the socket extension bar in the chuck with a square to hex adaptor.

Even the biggest drill bit you have inside a hose taped to the shaft should do it.

[57paulimo]

Brilliant idea oldman2! Job for tomorrow.

[A1an]

When you replaced the pump impeller…the old pump…was it missing any of its fins?

[Jon Tallis]

Originally Posted by 57paulimo

Guys, can anyone tell me what would be the outcome of me putting too much oil into the petrol?
When I had the waterways cleaned of salt and crude, the guy convinced me to ditch the auto lube and to add oil to my fuel each fill up.
I really, really hope I haven't added way too much oil to the fuel I've been using..........

Too much oil causes lean mixture and overheating (more oil = less petrol = lean mixture).
Also, on an oil-injected engine (assuming yours is designed to inject oil downstream of the carbs), the carb jets won't be sized for running pre-mix and this will throw your mixture out further.
Questions...
What was his reason for advising you that?
How do you know what mixture the engine is designed to run on (it's not stated for most oil-injected engines)?
What mixture have you been running?
How has the oil-injection system been isolated? You could have further air-leak paths if not isolated properly causing even leaner running.

[57paulimo]

Thanks for replying Jon.
I'm a complete novice, this is my first boat, very green. His reasoning at the time was that if the oil injection failed for any reason it would cause a whole lot of damage, and he had removed the oil injection system from his own engine.
The ends of the oil pipes are sealed with what looks like 6mm s/a bolts held in with a clip.
Anyway it is what it is. I was told a 50-1 mixture would be fine, but thinking back to 2019 I seem to remember putting more than that amount in.
So, I buy and fit new gaskets all round, reassemble everything, buy brand new petrol , ratio 1litre of fuel to 20ml two stroke oil.
Remove all existing fuel from engine filter and fuel lines.
I hope the mixing of the oil and petrol is done after the carbs, or they will need to be stripped and cleaned as well.
Been out of the water 2 years now, no end in sight........

[57paulimo]

Jon, please ignore my sentence about the petrol and oil, I'm stupid.
Sorry. Carbs will need cleaning.

[TmMorris]

If you know that your mixer works then I would revert to that if only to rule it out.

Generally, not enough petrol going in will cause excess heat so things like a carb blockage, an air leak or too much oil.

But it's plausible that your carb is set up for pure petrol and now you're putting petrol with 2-3% oil through it the set up needs changing. It shouldn't make it lean as the fuel most entering the cylinders should be the same which way round you add the oil but it would be plausible that the jets are wrong for doing what you're doing.

Friction is also a trigger, so if something is rubbing and putting pressure on the engine.

What has me confused though is the seeming speed at which the telltale water becomes so hot. Whether it ever gets all that warm is down to where in the plumbing it is fitted and engines vary but from what I can understand it is getting very hot very quickly after start up?

That tends to make you think about a water restriction typically one would guess a jammed thermostat meaning the water volume in the engine is tiny. Possibly a blockage after the telltale.

As far as I can tell you've tested that a good amount of water is being sent up by the impeller, you've removed the thermostat and you've had a good flow of water out the exhaust from a hose into the thermostat housing,

The odd thing is that at this point you moght start suspecting a cracked head, water mixing in the cylinder etc but a clue you'd expect to find would be one plug looking different. However, I'd still look further down that avenue because of the speed of the overheating. I would get a temp gun on the cylinders and the telltale to get those numbers but I'd definitely do a compression test.

The other thing I would do very quickly is, assuming the water in the telltale comes straight from the jacket and isn't mixed with the exhaust gasses as the main flow of water out the leg will be (?), is to drain and refill your water bucket with clean water then collect a half pint of it as it exits the telltale and leave it to settle. This is why I was wondering if you had a plumbing diagram for your engine because if the telltale exits prior to the water being mixed with exhaust gasses then you'd expect the first load of water out from a clean bucket to be clean and free of oil?

However if all the cylinders are the same temp and all have the same and good compression then this would, given water not an issue, push you back to look at the fuelling.

[Jon Tallis]

Paul,
I'm with Tim - if your oil injection was working fine I'd re-commission it. Hopefully the carbs weren't "tweaked" for premix and wills till be set ok.
...oh ...and find a new mechanic....whilst he's right in theory, manufacturers introduced oil injection to increase reliability, not to decrease it.
Back to your overheat problem, unless lean running has caused catastrophic damage and very high friction, your engine is getting too hot too quickly to be just related to fuelling - my money is still on a water blockage or leakage somewhere.
I'd probably run a compression test though.....if you have caused damage you'll see it first on a compression test. At least that way you can say that the basic mechanics of your motor are still good

[TmMorris]

Paul,

Have you had the cylinder head off or the cover?

I'm trying to guess where the telltale feeds from but could it be from the cylinder head and the thermostat housing hen opens the rest of the system up?

When you pump water back up the telltale do you get it happily coming out the main water exit into the leg?

If I recall you've put water in via the thermostat and it's clear. You've also pushed water up from the main feed from the impeller and does this come out of the telltale as well as the thermostat fitting and definitely out of the leg having circulated the engine?

I'm trying to work out how the engine could be getting so hot so quickly and for the telltale to be so hot. For example, if you had a snug hose fit over the feed from the impeller is the water coming down the leg as hot as the telltale water?

I'm just wondering if the telltale feed is from around the cylinder head with the thermostat opening up the remainder?

But I think you need to do a compression test first to rule that issue out then revert the oil feed to how god intended and to be honest, take the carbs off and give them and the jets a clean.

[57paulimo]

TM Morris, thanks so much for your invaluable help.
At present I have.
Both exhaust manifolds and gaskets off.
Both water jacket and cylinder head and gaskets off.
Every waterway, channel and hole are all completely open and there is definately no blockage anywhere that i can see.
I've checked the thermostat, overheat alarm sensor, and water pump (3 times). All 3 plugs look the same colour albeit a bit oily.
The water uplift pipe isnt perforated, it can only be my stupidity in mixing the two stroke oil to the petrol that's put me in this mess.
Thanks.

[paintman]

The older Mercury V6 two-stroke engines used an oil injection system.

The oil being fed into the petrol line well before the carbs so arrived at the carbs already mixed.

The higher the revs the faster the oil pump turns and the more oil is dripped into the fuel line, AIUI being around 100:1 at idle and 50:1 at full throttle with variation between the two.

Common for these engines to have the oil injection system removed and Mercury supply a factory kit to do so.
Once removed the recommendation is to run on 50:1 premix.
Although mine is as original I have done a LOT of research over the years and haven't found any claims of issues caused by running 50:1.

That said, if it ain't broke don't fix it and if you can reinstate your system to normal operation then you will have eliminated that as a possible cause.

FWIW I also run a Suzuki DT4 as a back-up/trolling motor and the factory manual gives premix of 100:1 apart from if the motor is being used commercially or in South Africa when 50:1 should be used. At 50:1 it's slightly smokier but it hasn't caused any problems.

[TmMorris]

Originally Posted by 57paulimo

TM Morris, thanks so much for your invaluable help.
At present I have.
Both exhaust manifolds and gaskets off.
Both water jacket and cylinder head and gaskets off.
Every waterway, channel and hole are all completely open and there is definately no blockage anywhere that i can see.
I've checked the thermostat, overheat alarm sensor, and water pump (3 times). All 3 plugs look the same colour albeit a bit oily.
The water uplift pipe isnt perforated, it can only be my stupidity in mixing the two stroke oil to the petrol that's put me in this mess.
Thanks.

That's all positive for ruling out water flow.

Plugs being a bit oily is probably OK as the engine needs less oil when pottering so a fixed mix of say 50:1 would be a bit rich at idle as mentioned above but not an issue.

I'd still do a compression test to rule out head damage that's causing increased friction ergo heat or water leaking in. Gaskets can also be an issue, you don't need any cracks to trigger overheating, a leaking head gasket can do it easily enough.

If compression is good and all the gaskets are good then you almost know for sure that it is fuel. Maybe too much oil, maybe a dirty carb but you can usually hear that sort of issue in how the engine runs, smokes etc. But that tends to be easier when you're around a lot of motors and your ears are tuned in and as you've had this issue for a while and not been using the engine it might be hard.

There's probably no harm in mixing up a 100:1 for testing purposes as you don't need to rev the engine, load it up or use it for long periods and a thin mix would assist in proving a fuelling issue.

I just feel that you'd need to have a lot of oil in your mix to get close to the issue you're having whereas water getting in to the combustion chamber would almost certainly show itself via the symptoms you're seeing, hence why a compression test now you are 100% sure the water ways are clear and flowing would be might next port of call.

Ultimately, if you have a nice flush of cold water going in and around the engine I'm still not sure why the telltale would be getting that hot, that quickly but the answer to that and the actual issue could lie in knowing where the telltale exit sits in the whole plumbing network as I believe they are different for different engines.

For example, smaller Yams than yours have the telltale just after the water arrives in the powerhead. That means it'll flow so long as the pump is working but by no means would tell you if water was also flowing around the engine. In that set up I'm pretty sure that the only way the telltale water could get too hot to touch within a very short time of firing the engine up would be if water wasn't circulating the rest of the engine. That's a classic sign that the thermostat is broken and stuck closed. The flow in can't go further around the engine so just superheats what's in there and bins it out the telltale at a very high temp.

But you've run this engine without a thermostat haven't you? So this has been ruled out 100%? Likewise you've confirmed that there is a good flow of water coming down the engine exhaust when running which would also mean it's flowing all the way through.

That's the conundrum for me, overheating from a fuelling issue or most other causes tends to be more gradual whereas I've taken the impression that the telltale starts getting hot very quickly?

[TmMorris]

As an aside, I recall you had the engine water ways cleaned was this due to the engine running ok during your ownership and then starting to overheat in use or due to it always having an overheating issue ever since you got hold of it?

If there was nothing wrong with the galleries and water has been flowing well then can you describe how the over heating began? Was it suddenly there as it is now or has it become worse in use to where it is now?

I'm trying to think whether a gasket leak could allow enough gas pressure from the engine into the main galleries to halt water flow hence why all your symptoms tend to suggest a blocked thermostat which we know isn't the case?

2 strokes are pretty high pressure could a leak in a key place into the water ways effectively halt the flow?

Are there any signs around the outside of the engine of a leak? There might not need to be if it's somehow internal.

A comp test is going to show if there is a gas leak. You could try a Yorkshire compression test which is to take the leads off the plugs, then haul the start card of a few time then use you best ear for hearing paper money at 100 yards to listen for any leakage?

[A1an]

can you post a picture of the exhaust/water jacket now you have the side plate off?

[TmMorris]

Paul, as you can probably tell I'm quite interested in your conundrum. .

The speed of heating up and the heat of the telltale seems impossible to explain by the gradual over heating caused by lean running.

Assuming a blockage after the telltale seems the correct thought process. For such a quick and significant effect it has to be that water is coming up the shaft, into the powerhead, into the section next to the exhaust where the telltale exit is but not flowing behind that.

We've ruled out the two most obvious causes of blockage which are a kaput thermostat or a gallery blockage so it's a matter of trying to work out what else could be creating a blockage as that is surely what is happening here. The telltale simply couldn't get that hot or do so that quickly unless the coolant from the bucket was not able to flow beyond the initial reservoir into the rest of the system. I do think that it is catagorically due to a blockage.

The only other form of blockage that I can think of is a gas blockage. That would explain why you can't see it, why you can't synthesis it because it doesn't exist under test conditions but rather it is being caused by the high pressure exhaust gasses when running, escaping through a crack or gasket into the low pressure cooling system and halting the flow of water.

A minor issue may have caused your engine to initially overheat, maybe something unconnected to the issue now such as lean running etc but the major issue now is coolant blockage and having ruled out the obvious causes the only remaining cause I can think of is gas pressure exceeding water pressure and weight which given you have a high pressure gas system running next to a low pressure water system and only separated by thin metal walls and little gaskets, does fit as the potential
Issue, if not the initial issue.

Have you or anyone ever taken the head off during the period of ownership?

Can you see any signs, internally, of gas passing to the water system?

You mentioned something that looked like a crack in an earlier post?

But ultimately, what are the compression numbers on the three cylinders? To eliminate this blockage theory all that's needed is three identical compression readings that all hold that number steady.

I think a compression test will deliver a pretty binary outcome in that we will either have the source of the blockage or start having to consider asking Derek Acora for his explanation.

[TmMorris]

Also, did you do a compression test when first checking out the engine? Can you recall what the readings were?

[Jon Tallis]

Originally Posted by paintman

The older Mercury V6 two-stroke engines used an oil injection system.

The oil being fed into the petrol line well before the carbs so arrived at the carbs already mixed.

The higher the revs the faster the oil pump turns and the more oil is dripped into the fuel line, AIUI being around 100:1 at idle and 50:1 at full throttle with variation between the two.

Common for these engines to have the oil injection system removed and Mercury supply a factory kit to do so.
Once removed the recommendation is to run on 50:1 premix.

All good info but the OP's engine isn'ta Merc V6, it's a Yam 70