Tohatsu 3.5Hp - not cooling.

[Devs Ad]

This is a low-hour, sweet-running, good-compression little motor, but there's no water from the tell-tale.

Finger near the t-t suggests it seems to be pumping 'air' - you can feel 'pulses'. Local service shop has replaced the impeller to no benefit, and will be digging deeper when time allows (busy time of year).


Meanwhile, anyone got any ideas? It seems a mystery to me - why would air be pulsed out, but not water?



Thanks for any suggestions.

[Limecc]

I checked the impeller on mine and all was well, still a little reluctant. Needed a deeper bucket and more water.

[babbot1]

I don't have the same motor but maybe similar issue. When this happened to me after an impeller change it turned out where the water tube connects to the powerhead, the tube crushed the gasket blocking almost all the flow. I had to pull the lower unit off again and carefully connect it making sure it was aligned just right.

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Thank you both.


Lime, Thanks, but I'm assuming the service engineer knows how deep he should be immersing the motor in the water. I have few doubts about his competence - he's very experienced.



Babb, yes I suspect something like that. The weird thing is the 'air pulses', tho'. I'm assuming it's air and not exhaust, as it wasn't visibly 'blue' or smoky, tho' I can't rule it out. Is there a way for exhaust to leak into the water jacket?


Or, if it's air, that would suggest to me it's drawing in air from the outside before the impeller, so somewhere between the impeller and the water inlet nozzle - is there anywhere?

[Limecc]

Originally Posted by Devs Ad

Thank you both.
Lime, Thanks, but I'm assuming the service engineer knows how deep he should be immersing the motor in the water. I have few doubts about his competence - he's very experienced.

So what does he say?

Originally Posted by Devs Ad

that would suggest to me it's drawing in air from the outside before the impeller, so somewhere between the impeller and the water inlet nozzle - is there anywhere?

No it's all submerged. Probably best to run it on flush muffs in case it's drawing on exhaust gas in the water.

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He says he needs to investigate further, which he will do (busy time of year taking boats out of the water and moving them around...)


I was just hoping someone would meanwhile say "Ah! I had the same issue...!"


Thanks - so the impeller is below water level, which makes sense - it'll self-prime.



I wonder if, for some reason, it's not doing its full job, but is making the water around it pulse upwards - tho' not far enough to flow right up - and this 'bobbing' water is creating the air pulses? Ie, air isn't being ejected out the TT, but is pulsing back and forth?



Anyhoo, probably no point speculating - I'll just have to wait until he can strip the motor down further.



Cheers.

[babbot1]

Originally Posted by Devs Ad

Thank you both.



Babb, yes I suspect something like that. The weird thing is the 'air pulses', tho'. I'm assuming it's air and not exhaust, as it wasn't visibly 'blue' or smoky, tho' I can't rule it out. Is there a way for exhaust to leak into the water jacket?
?

Hard to say without pulling it apart but to speculate further it could still be similar to what I had. The gasket wasn't completely closing off the water so it did steam a little. I didn't run long and knew something was amiss. It will overheat quick so don't run it long without water flow.
The other thing could be a piece of old impeller stuck somewhere upstream or some other clog that is stopping proper flow but that usually just slows the flow not catching air.
Let us know what it is when the mechanic gets to it. Very curious.

[Matt]

I didn't know you can get flush muffs small enough to fit a 3.5hp? Anyway, if I'm doing a bit of diagnosing on a motor with no clutch or gears (@OP, I'm unsure about this model, sorry), I usually take the prop (and remember the shear pin) off to run it in a bucket/bin. Stops all the water swirl which, you can sometimes get a circular wave form in the bucket meaning the prop is in the water, but the inlet isn't.

Sounds like something isn't quite right though, for example, on both my small motors, it's easy to lose the little black seal that seals the water pump housing outlet to the pipe going up the leg. I've had a "sticker" before as I pushed the pipe in to the seal it deformed & displaced it rather than sealed it.

[Devs Ad]

Thanks Babb and Matt.


I have to say that a break in a gasket or other faulty seal does sound like the most likely cause.


I will report back when the guy has had a chance to investigate further - thank you all.

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Seems there was a blockage in the waterway just under the engine block - needed quite a bit of investigation/dismantling. But seemingly all working well now.


Cheers all.