PLEASE HELP........Outboard Overheating - ADVISE PLEASE

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petri oosthuizen
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PLEASE HELP........Outboard Overheating - ADVISE PLEASE

Post by petri oosthuizen » Tue Jun 04, 2019 12:52 pm

Hi Guys

I have a Tohatsu 40 HP 2stroke that gives me headaches.

It overheats, but does it intermittently. Sometimes within a couple hundred metres, sometimes after an hour.

I did the Head, new pistons and rings (sommer net), new impeller, teh whole toot.

Engine starts and runs like new.

I had it serviceg in Nigel again last week, very reputable guy. He replaced the impeller, which was pretty buggered.

He reckons its the grass and weeds in our dams that clogs up the intakes, resulting in the engine overheating.

Yesterday, I sent my 2 boys to a cleaner dam, to test it.

Same story - it overheats intermittently.

I put muffs on the inlets this morning - it runs like a new engine, all water outlets 200%.

I also put it in a drum so that it sucks "by itself" - as above, runs like new.

I'm sure the impeller is burnt again, so off to Nigel again to replace a damn R 60 part

Mechanic reckons its grass/weeds in the dam........I dont want to argue, everything does point to that, but HELL, can an outboard be SO sensitive to that?? He;s not talking grass/weed IN the engine, he reckons the grass clog up the intakes from outside........if you then stop and start again, the engine is 200% again. This makes sense I guess...........

PLEASE help if you can, we need this without any faults for our Katse trips coming up

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Pugwash
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Re: PLEASE HELP........Outboard Overheating - ADVISE PLEASE

Post by Pugwash » Wed Jun 05, 2019 7:52 am

I had an old Merc 4hp that did that.... It was the bane of my life. I fixed it by buying a new motor.

Just as a point of interest, is the telltale still pushing a solid stream while it's in overheat mode?

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landshark
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Re: PLEASE HELP........Outboard Overheating - ADVISE PLEASE

Post by landshark » Wed Jun 05, 2019 10:39 am

Hi Petri,

Your mechanic is most probably spot on, restricting the water flow to a water cooled engine will cause it to quickly overheat but there are be some other things to also check that may cause intermitted overheating.

I take it since the engine had a in depth service the thermostat was also replaced? This would be the first place I'd look and something which may cause the symptoms you describe. Although the overheating is intermitted, which will make testing the thermostat and marking that as the problem with 100% certainty difficult, a way checking is to run the motor on muffs and keeping your hand under the tell-tail water. Initially when you start the motor you will feel cool water and as the motor heats up the water temp will increase, if the thermostat is functioning correctly the water will heat up to a certain point and then you will feel it cool down again - this is the thermostat opening and closing allowing the water to either enter or bypass the internal engine cooling channels. If the thermostat is the problem then it should be a quick and cheap fix to replace it.

If its not the problem then it may the cooling channels themselves causing the issue. After extended use these may become clogged up with corrosion, silt and other gunk. If the blockage is not too bad, you may get away with doing a extended (12 hours) flush with a cleaning product such as Salt Away. White Vinegar, although not as effective, may also do. Running your motor to circulate the solution for 12 hours is not really practical so the best way of doing it is to remove the gearbox and fit a pipe with a small pump (a small bilge pump should do) directly to the bottom water inlet (the inlet where the impeller would push water up to the motor) then dropping the pump into the solution and letting that circulate. You will also have to remove the thermostat in order to make sure the solution circulates through all the engine cooling channels.

If the build-up is more serious and the flush does not solve the problem then the only other option would be to try and clean the cooling channels manually. This is big job as the engine will have to be completely stripped to in order to access them but if all else fails may be your only option.

petri oosthuizen
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Re: PLEASE HELP........Outboard Overheating - ADVISE PLEASE

Post by petri oosthuizen » Wed Jun 05, 2019 10:41 am

Pug, the overheating is caused by water not flowing any more.

My (very reputable) mecchie reckons its grass blocking the inlets, BUT we have tested the boat on a cleaner dam, and still the same.

I have it in a drum now, have started it up maybe 20 times, NO issues at idle or higher RPM or whatever - runs 100%.

I have noticed the thermostat has been removed, dunno why.........not sure if this could be the issue, I have a feeling it is. Ordered a new one from Marine King.

The "open channels" now eher the thermo was is somehow maybe too "open", with water flowing in the path of "no resistance", that may be the issue here.

Hope you understand what I'm saying here??

petri oosthuizen
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Re: PLEASE HELP........Outboard Overheating - ADVISE PLEASE

Post by petri oosthuizen » Wed Jun 05, 2019 10:47 am

@ landshark - see above post, thermostat is removed, I only saw that yesterday.

I actually didnt really worry about it, but I've read a thermo IS a must on an outboard, channeling all the water.

When I let the engine idle for long (15 min) in the drum, the water at the exhaust outlet gets quite hot........but telltale stays cold.

If I rev it a bit, the water squirts nicely out of the zost outlet, and cools down almost immediately to lukewarm (almost colder than lukewarm).

Telltale stays cold the whole time, I think almost too cold??

Thanks a MILL Guys 8-)

petri oosthuizen
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Re: PLEASE HELP........Outboard Overheating - ADVISE PLEASE

Post by petri oosthuizen » Wed Jun 05, 2019 12:54 pm

...........Guys, whats the verdict - could it be the thermostat (or in this case the NON thermostat)...?? :o

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landshark
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Re: PLEASE HELP........Outboard Overheating - ADVISE PLEASE

Post by landshark » Wed Jun 05, 2019 3:50 pm

Since there is no thermostat you can safely say it's not that which is causing your motor to overheat.

The channel which feeds water to the thermostat housing chamber may be blocked, so it may be worth checking that, but for me it points to the cooling channels in the block itself - especially since you mention that the exhaust water cools when the motor is under load which indicates that certain areas in the block only receives cool water once the water pressure increases.

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Re: PLEASE HELP........Outboard Overheating - ADVISE PLEASE

Post by boatmatix » Wed Jun 05, 2019 9:15 pm

The fact that your thermostats have been removed points to an existing overheating problem that could not be resolved, usually clogged cooling channels and the easy way to remedy is to remove thermostats.
Problem with that is your problem is still there and once the channels clog more you have the same problem.
How does it look in the thermostat housing, that’s often an indication to the rest of the cooling area condition.

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Re: PLEASE HELP........Outboard Overheating - ADVISE PLEASE

Post by rory » Sat Jun 15, 2019 8:07 am

Go get a few bottles of vinigar put those onto your bunny ears and run till it comes out you can catch it in drum and reuse, let this sit for a few hours and then repeat it will clean out all the corrosion and could help

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