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Damn...

My M40D Outboard has given perfect service for 4 years, until yesterday......

Salt water used, not flushed with freshwater for a while (as Summer season boat yard has no facilities)

As always, started fine, motoring along great, with pee hole ok. suddenly, extreme overheat, with smoke coming out from under the cowling. No overheat sensor fitted

Engine died. Engine very very hot! (a plastic screw plug in the cylinder block melted) 30 minutes to cool down, started fine and ran well, did not get hot again, pee hole fine.

But after stopping and fishing for 2 hours, engine very difficult to start, running at half speed, sort of droning along.
While under way, pulling lead off plug 3 made no difference to revs
So cylinder three not working...
Would it be related to the overheat, or a coincidence?
Why would cylinder three die? a new coil perhaps?

Haven't tested for spark on cylinder 3 yet (I need to get the boat home first),

Now thinking about my problem whilst at work...

Could this be a likely scenario?

Engine overheats
Causing a water leak into no 3 cylinder because of a warped head/bust head gasket
At first engine runs fine
but water seeps in over a couple of hours
which makes it hard to start and stops the "wet" cylinder from firing, so that it only runs on two cylnders

If I get a spark from no 3 coil when i get the boat home, would that prove my theory?

Is taking the head off to replace gasket, get head skimmed a fairly easy operation?

BTW.. as for the overheat alarm, there are a few wires not connected to the control box end, I thought they were for any guages fitted, maybe there is a overheat wire not connected too, the low oil alarm works fine however

Please help because the Cod will be here soon!
 

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Sorry Codling that doesn't sound too good. The plastic plug was probably the cap blowing off the thermostat. Had that happen to me on a prveious motor due to an overheat. I was lucky and got away with minimal damage.
You obviously need to check your compression on all the cylinders. The one that is not firing could have partially seized. The rings may be stuck in their grooves in the piston. You might be lucky and find it is only he plug tip electrode is whiskered up when it overheated but it may have melted too.

For starters in no particular order see if you have a spark on that plug lead. OK? Then check the compression with a compression tester. If the compression is down on the 3rd cylinder. You have a major overhaul ahead. And if okay and the same or near as in the other two cylinder figures. To be safe you need to replace the thermostat.
The system may have been glogged up from you not flushing out the salt and caused the overheat. The thermostat could have failed. The water intake may have been blocked. Lots of things can cause an overheat. Impellor blades broken, crap/weed sucked in etc.
If all the above checks out okay. Replace the impellor or be very sure it is pumping water before starting it and running it for any length of time again. Make very sure you have all the cooling water passageways clear and cooling water circulating through the motor or you may have the same overheating problem again.

I have the same motor the 50hp version. Not had to take the head off - and never hope I will have to! Looking at it. It is a job that could be done without dismantling too much. You would not be able to skim the cylinder side insitu though also If the piston is goosed you have no option but to take the powerhead apart.

Good luck!
 

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As always, started fine, motoring along great, with pee hole ok. suddenly, extreme overheat, with smoke coming out from under the cowling. No overheat sensor fitted
Was there any water coming out of the main water escape or just the pee hole whilst you were running Chris ?
 

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Thought I would let you know the outcome....

A week after the overheat I got the engine home

No compression tester so couldn't do a compression test
Although using a finger bunged in a spark plug hole, there didnt seem much compression, not a very accurate measure, I know!

Stripped the head, which was a fairly easy procedure, with no seized bolts etc

Cyl head gasket looked a bit dodgy but no obvious splits

Cylinder bores and pistons looked fine, a tiny bit of scuffing on cyl 1

Checked the thermostat, was OK

Replaced 2 exhaust, 1 water and the head gasket

New spark plugs

Oil pipe had melted (fortunately not completely through) so repaired and bled that

Anxiously turned key, And the engine started

Pumping water fine

Took the boat out today. It went fantastic, better than before, ticking over sweetly

Will put a temperature sensor and buzzer on this week

During the work, it struck me how good the quality of the engine components were, no rounded screws or corroded nuts

Thanks for the advice guys
I can go fishing again
 

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I haven't the faintest idea, a plastic bag maybe:unsure:
After it had cooled down, it pumped water ok
And there doesn't seem to be any damage to the impellor

Knocked my confidence a bit though!

I've just bought an as new 4Hp Suzuki as a back up

And i am trying to get the bits together to fit a temperature sensor
(any advice would be welcome)

Thought about this: http://cgi.ebay.co.uk/ws/eBayISAPI....om=R40&_trksid=m38&_nkw=230283078466++&_fvi=1
Only problem is that there is no buzzer

But over all a good result:happy:
 

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I haven't the faintest idea, a plastic bag maybe:unsure:
After it had cooled down, it pumped water ok
And there doesn't seem to be any damage to the impellor

Knocked my confidence a bit though!

I've just bought an as new 4Hp Suzuki as a back up

And i am trying to get the bits together to fit a temperature sensor
(any advice would be welcome)

Thought about this: http://cgi.ebay.co.uk/ws/eBayISAPI....om=R40&_trksid=m38&_nkw=230283078466++&_fvi=1
Only problem is that there is no buzzer

But over all a good result:happy:
If that's waterproof enough to keep working it looks like a good idea. I'd still do what SurenuffandyesIdo suggests though-check the impeller (isn't that the same impeller as the 50 which can be run dry?)and compression test it fairly regularly for a while as scuffing on one bore may mean it's ripe for the piston picking up.
 

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Ok differn't motor suzuki dt 30 had a over heat melted the cdi unit mine is a two cylinder single cdi unit and £300 later sorted does your have 3 sepates units speak to international marine supplies in my opion very good.
 

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Mine has one CDI unit and 3 seperate condensors

I've been in contact with Dave Bakin from IMS
Very helpfull, he got me all the necessary gaskets within a couple of days

One thing Dave warned me about, is when checking for a spark you MUST earth the plug, or the CDI can go bang!

As for the impellor, it seems pretty indestructable, but I think i will put a new one in anyway

But i'm a bit concerned about disconnecting the gear linkage, there seems to be two pins to push out, but it all looks a bit flimsy, has anyone done it before on a Tohatsu?
 

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