Tohatsu M40D firing on two cylinders after overheat

[codling1]

Hi
M40D Outboard has given perfect service for 4 years, then today......

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

A few weeks ago, on two occasions, while running, engine would only go to half speed, as if running on two cyls, then kicked in, and ok. I dismissed it.

Started fine today, motoring along fine, 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, then running like it did a few weeks ago, on 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 neeed to get the boat home first), plug was oily

Any advice would be welcomed, as I am in England where Tohatsu service centres are few and far between

 

[chevyjet]

Re: Tohatsu M40D firing on two cylinders after overheat

first check your compresion, you need all 3 to be with 10 or 15 % then change your spark plugs, and look in the plug caps for corosion.

 

[TOHATSU GURU]

Re: Tohatsu M40D firing on two cylinders after overheat

Probably a momentary obstruction of the water intake due to debris being sucked to it. You stop engine, the debris falls away and you are left with an overheat that suddenly cures itself. Now you are left with possible engine damage to the block and possibly damage by heat to the ignition system. Swapping an ignition coil from # 2 to # 3 will tell you if that is fire problem A compression check is mandatory before running the engine again. Make sure the readings are even across all three cylinders. Don't worry about the actual number itself. If the compression is even just torque the head back down before using it again. The 40 D hand tiller engine does not have an overheat sensor, however the remote model does have one and it should sound a buzzer inside the control box.

 

[deejaycee_2000]

Re: Tohatsu M40D firing on two cylinders after overheat

Sometimes it happens that you pick up a plastic bag and cause this .... I can allready tell you you have hardly any compression on that cylinder, which means you need to strip and replace the piston and rings .......

 

[codling1]

Re: Tohatsu M40D firing on two cylinders after overheat

Thanks for your comments guys
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?

And finally will the engine sieze if I leave the boat in the compound for a week with salt walter in the head...I am on vacation until Thursday, starting tommorow morning and cant get to my boat until then!

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

Thanks in advance...

 

[TOHATSU GURU]

Re: Tohatsu M40D firing on two cylinders after overheat

"And finally will the engine sieze if I leave the boat in the compound for a week with salt walter in the head"

Bad idea as any damage can only be magnified by allowing the engine to sit.

Removing the cylinder head is a straight forward operation. You will have to have a new head gasket and a torque wrench to put it back on. Check and see if you have a temp sensor in the cylinder head. If you don't, pick one up and plug it in to the existing wiring harness. It's always possible that it was never put on or was removed.

 

[chevyjet]

Re: Tohatsu M40D firing on two cylinders after overheat

If you absolutly can not work on the engine right away put a bunch of 2 stroke oil in the top end or foging oil and turn it over by hand, then pull it apart as soon as you can.

 

[codling1]

Re: Tohatsu M40D firing on two cylinders after overheat

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

 

[ziemann]

Re: Tohatsu M40D firing on two cylinders after overheat

Congratulations- it sounds like you dodged a bullet!

I was think'in that DeeJayCee was probably right and you had toasted a cylinder...

Glad to hear that it was minor and you are back up and running!