Water uptake.

57paulimo · 04 September 2021, 17:04

I need help once again, I'm getting to the end of my patience, knowledge and tether!
I've changed most things on the water uptake on my Yamaha 70hp outboard and I'm still getting the engine overheat alarm going off.
Question. How does the water pump housing connect to the engine water intake?
I've had the thermostat housing off to check water flow, I've rebuilt the water pump and oil seal housing beneath.
I've ran the engine in a barrel of water and also with muffs, it makes no difference.
I noticed water coming from the back of the lower unit just above the water intakes.
Question. Does all water from the pump get to the engine casing or are there places where water can escape.
I've currently got the engine raised ready to remove the bottom end once again to recheck the impeller.
Any help would be most welcome.
Paul.

Davie · 04 September 2021, 17:28

Have you ever seen this engine cool? I had this very issue and what had happened is the owner had fitted an early box to a late (2007+) engine. Top secret but Yamaha changed the water pump to a 688 type meaning the water pipe in your engine may be to short to reach the grommet in the plastic housing. Measure from the surface of the leg to the end of the pipe then measure the the height of the grommet to check this.

A1an · 04 September 2021, 21:02

Quote:

Originally Posted by Davie

Have you ever seen this engine cool? I had this very issue and what had happened is the owner had fitted an early box to a late (2007+) engine. Top secret but Yamaha changed the water pump to a 688 type meaning the water pipe in your engine may be to short to reach the grommet in the plastic housing. Measure from the surface of the leg to the end of the pipe then measure the the height of the grommet to check this.

Every day is a school day

57paulimo · 05 September 2021, 15:24

Excellent pointer Davie.
Just been out and measured the end of the uptake pipe, 20mm up from the mating face.
The uptake pipe should fit well into the impeller housing, and seal via the rubber "O" ring that's in the housing.
I've just rechecked the impeller for damage and it looks fine.
Question. Where does the uptake pipe goto inside the upper part of the leg? Is there a joint/connection to the engine block?
The manual I have doesn't make it clear.
The next/final thing I'm going to try is to remove the water jacket off the block, and check it was cleaned properly by the guy I paid to do the engine cooling waterways.
Then I'm afraid I'm going to have to buy a replacement engine.

57paulimo · 05 September 2021, 15:29

Can I somehow connect a hosepipe to the water uptake with the bottom of the leg removed?
Where would surplus water go that isn't expelled from the tell tail?
I'm clutching at straws now........

Oldman2 · 05 September 2021, 15:29

Can you not connect a low pressure water supply to the tube up the leg from the pump, assuming you still have the water pump off, and see if you get flow around the engine?

Snap, posted at the same time.
The water should go through the engine and out the prop mostly so with the bottom off it will just spill down the inside of the leg.

TmMorris · 05 September 2021, 20:15

Yup. Connect a garden hose to the intake tube while the lower leg is off. As Oldman says the bulk of the water will come out the leg and the rest through the telltale.

Can you get the heat warning when running in a bucket?

If so then you could run it until you get the warning then turn off, remove the thermostat, replace the housing and run it again to see if you get the heat warning again.

Do you by any chance have a temperature gun to hand? It might be beneficial to see what the engine casing temps are close to the pistons before and after the warning is triggered.

Is it a 4 stroke? If so have you checked the engine oil for any milky residue?

If you're getting a good pee from the telltale and plenty of water down the leg (assuming a snug hose fit when you put the garden hose on it then this would suggest that the water galleries are clear, if you're still getting the alarm when the thermostat isn't fitted and if you're not seeing any significant jump in temps on the block before and after the alarm and the engine oil is clean then there is a chance that it's actually the temp sender unit that is at fault. I assume there is one screwed into the block somewhere in order for the ECU to get an alert?

Also, what are the other issues you've had with the engine and their fixes?

TmMorris · 05 September 2021, 21:40

Just pondering things. If there is a blockage in the system then a garden hose should fit in the thermostat housing and you might find some shell debris etc getting flushed out the bottom. Muck that has been sucked in can often be lodged towards the base of the powerhead.

But, if the galleries were all cleaned out and nothing has been drawn in since then have you considered that the over heating could be due to the other normal suspects:

Wrong oil mix if a 2 stroke.
Running too lean a fuel mix.

A bit of fuel starvation or insufficient oil can trigger overheating.

57paulimo · 05 September 2021, 22:27

Many thanks Tim for your thoughts.
The engine is a two stroke three cylinder.
I have had the engine running well probably 2 years ago with lockdown etc.
I went to take my grandkids out for a run, but on firing the engine up with choke and slowly reducing the choke the overheat alarm came on, causing us to curtail our trip.
I have since, rebuilt the water pump housing (oil seal housing), checked and changed the gear oil (it was fine), fitted a new thermostat, had the engine waterways cleaned out. The impeller looks fine.
Tell tail seems to reduce as the engine revs reduce (normal I suspect), but when the engine is running with the choke on slightly (to keep the tell tail flow going), but as the engine revs get low, the tell tail reduces and begins to get VERY hot, alarm starts sounding and I switch off the engine.
I've set the three idle screws as per manufacturer's recommendations. Next I'm going to remove the water jacket and cylinder head and check the passages are clear, then that's me done!
Paul

TmMorris · 06 September 2021, 06:24

Fair enough.

To 100% rule out the impeller have you spun it up in the bucket with a power drill and had a nice pour of water from the top of the leg?

What's the look of the three plugs? Are they all the same, all dry and brown?

The issue with telltales for diagnosis is that you have to know where they are in the system. Do you know if yours is before/after thermostat, or even the water jacket?

It does sound as if you've sucked up a load of grit and blocked a gallery or the mechanic didn't clean them out. The water pump is pumping water and assuming the telltale heat isn't a red herring due to the exhaust gasses heating up the bucket of water? then unless there is no oil being mixed to the fuel, water flow seems the most likely culprit.

Of me, I'd be taking engine block temps with a gun through the cycle to overheating while keeping a hose running in the bucket to keep some fresh water flowing in to see what kind of heat spike was occurring, when in the cycle and if it was limited to one cylinder or all. Before that I'd also have the plugs out to see what they are saying.

I'd then run the cycle from cool without the thermostat in but the housing back on and time and take temps through the cycle from cold to see if there is any difference.

If no change at all then I'd take the thermostat housing off and aim to wedge the garden hose into the housing so as to get the least amount of blow back and with the leg off but the bucket to collect the water see how well it pours out the bottom, how that flow changes when you pinch off the telltale pipe or if by any chance a load of crud from below the galleries, under the powerhead comes out.

neil.mccrirrick · 06 September 2021, 10:41

Have you checked the gasket over the impeller? If that’s poorly seated or back to front it may well allow water to flow under revs when pressure is up but will do exactly what you describe when pressure is low

RoyP · 06 September 2021, 16:21

I had a merc 50 which alarmed out higher revs. did all the temp and water tests and found that the temp sensor was faulty..... just a thought

57paulimo · 06 September 2021, 18:51

Thanks for the input guys!
Tomorrows tasks.
Check spark plugs. Connect a battery drill onto the drive shaft and run the lower leg in the water butt. (The lower leg is removed at present). Put a hose into the thermostat housing and check for debris, (the stat is removed at present).
I'm a bit apprehensive about connecting a hose onto the water uptake and running the engine, as I'm unsure of the pressure of the water leaving the water pump, and I don't want the engine to be short of water.
Then finally I'm going to take the water jacket off and inspect the water channels, then I'm done.
Thanks for all your input.
Paul.

57paulimo · 06 September 2021, 18:55

One last thing. I have a multimeter with a temperature probe attachment which I've been using to check temperatures.
I've checked the opening temperature of the thermostat and I checked the tell tail just before the over temperature alarm went off,
50+°C.
Thanks everyone again.
Paul.

Oldman2 · 06 September 2021, 19:05

Quote:

Originally Posted by Oldman2

Can you not connect a low pressure water supply to the tube up the leg from the pump, assuming you still have the water pump off, and see if you get flow around the engine?

Snap, posted at the same time.
The water should go through the engine and out the prop mostly so with the bottom off it will just spill down the inside of the leg.

I wasnt suggesting running your engine with the garden hose onto the tube, just use that to see what flow your getting to places like the stat housing & tell tail. Maybe that tube is blocked somewhere.

Jon Tallis · 06 September 2021, 22:03

All good recommendations so far but to add my experience....
Definitely worth checking the temp sensor but if telltale is getting very hot then you have a genuine overheat problem.
It's fine in my experience to run the motor on a hose clipped into the water uptake tube, provided you've got good flow from your house - this will rule out (or rule-in) a problem with your water pump.
Also try running with the thermostat out - see what difference that makes.
You mentioned your mechanic cleaned out the water passages? How did he do it? If he rodded them through then he might have compressed a blockage and completely blocked a passage - temp gun will help you diagnose any local hot spots.
If you suspect a blockage then there are various threads on here about chemical cleaning - I've had good success with Rydlyme.
You could also have a perforated water uptake tube, best way to check is to shine a small torch up the tube and look for light escaping, looking up the main leg, or shine a torch up the main leg and scan the walls of the tube with an endoscope

Jon Tallis · 07 September 2021, 11:42

Quote:

Originally Posted by 57paulimo

Question. Does all water from the pump get to the engine casing or are there places where water can escape?

To answer this, all the water from the pump should get to the powerhead via the uptake tube (there should be no intentional leakage), this then cools the powerhead and is discharged into the exhaust gas in the top of the leg and exits via the prop, with a small amount diverted into the telltale jet

57paulimo · 07 September 2021, 20:29

Many thanks guys for your input.
Today I jammed a rubber tube connected to my hose pipe into the thermostat input, a few bits of sand, but nothing much.
Also jammed it into the thermostat output, which definately goes down the exhaust pipe work.
Removed and checked the three spark plugs for discoloration, a wee bit oily but all three the same.
I refitted the lower leg so tomorrow I can run the engine on muffs and take temperatures around the exhaust manifold, the cylinder head and adjacent to the high temp alarm area.
I'm fairly sure it's either a blockage or as Davie suggests, the water uptake pipe is possibly perforated!
Although the tell tail is fairly strong, reducing with engine revs, this only indicates the water pump is working, and it gets so hot you can't put your hand under it, which seems again to point to a blockage.
Thanks for all your excellent input, and especially Davie Anderson for his help!
Paul.

57paulimo · 08 September 2021, 11:26

As per Davie Anderson's pointers, today I've removed the lower leg once again and fit my hose pipe onto the water uptake.
There seems to be no leakage coming down from the upper reaches of this uptake which hopefully suggests it's not perforated.
The tell tail is strong, plenty of water coming out of the thermostat inlet and water coming down the exhaust part of the leg.
Next.
I'm going to remove the water jacket and remove/test the high temperature alarm.
I don't think its blocked in the exhaust manifold, but perhaps the waterways connecting to the water jacket/cylinder head.
The one thing I cant understand is the tell tail getting so hot when the engine is warming up??
Thanks again for all your invaluable input.
Paul.

Jon Tallis · 08 September 2021, 11:59

Quote:

Originally Posted by 57paulimo

The one thing I cant understand is the tell tail getting so hot when the engine is warming up??

You've got a genuine overheat problem there and sounds like quite a big one to be getting so hot so quickly. If youve got plenty of water getting into the powerhead then it can only be a blockage (big so hopefully easy to find), or the engine is generating way too much heat. Only sources of this would be running way-lean (and your plugs suggest it isn't) or a failed/seizing bearing. Let's hope it isn't the latter. Does it sound OK and turn over OK including by hand with the plugs out?
Keep us updated.....good luck