tohatsu overheat senser still going off

[realchuck63]

ok ok,,,whats next??

I've replaced the plugs twice. BR8HS-10,,New over heat senser 3N4-76172-1,,
New water impeller 3B7650212M
added a jack plate too make sure my motor was in the proper height range for my transom.
Checked for heat spots with a infer-red heat gun while operating my motor and found that
most areas held a 130-150 degree range..Right near my over-heat senser I read a temp of
170-180 degrees...Is that a normal temperature range???

I can run my boat ar 5200 rpm's all day,,push up to 5500 and within 1 minute my alarm sounds
and the rpm's start decreasing...Whats next??..I love this motor and I don't even use top speed..but I
really would love this problem too go away WITHOUT un-plugging my overheat senser..

Does anyone know at what temperature this alarm should be activating???

and by the way, I unplugged the senser and the issue went away, but i don't wanna loss that
safety valve!!!!

thanks
realchuck63

 

[pvanv]

Re: tohatsu overheat senser still going off

That sounds too hot. Tohatsu America at 214 420 6440 can confirm the designed heat level for triggering the switch. I suspect you have something either preventing proper cooling water in that area (such as a blockage) or insufficient water flow volume.

 

[Sea Rider]

Re: tohatsu overheat senser still going off

Which model engine is it and how old might that horse be ?

Happy Boating

 

[realchuck63]

Re: tohatsu overheat senser still going off

M70C year 2000

 

[Sea Rider]

Re: tohatsu overheat senser still going off

That's a 13 year oldie, when you change impeller or complete water pump kit, new thermostat and overheat problems continues forever, it's time for a complete crankcase, head maintenance. Your entire water passages may be salt narrowed, slightly blocked, clogged preventing good water flow in-out to disipate internal heat and cool down engine properly.

Take advantage to check all water paths from lower water screens, water pump rubber gromet going up water tube and it's gromet connectors to lower crankcase for dryness, deteoration, clean, decarbon pistons heads, cylinder head, check thermo cond, torque new head gasket and that horse will spring back to life.

Happy Boating

 

[TOHATSU GURU]

Re: tohatsu overheat senser still going off

I remember the temp as being 165, but I am probably off on the number. Regardless, the alarm could be triggered by a bad sensor or bad wiring, etc.

 

[realchuck63]

Re: tohatsu overheat senser still going off

Well I took my cylinder head off this weekend and found alot of salt narrowed passages..I'm not sure what decarbon piston heads means??
I've went this far, should I pull the complete crank case off and inspect the lower crankcase??..That area from the outside,looking at the 8 bolts holding it on, looks dry and I guess deteorated more than the rest of the motor and foot..and i just looked at my pistons and they have a dark carbon look on their tops..

 

[realchuck63]

Re: tohatsu overheat senser still going off

You were close, i called Tohatsu friday and they said 167 on that sensor..

 

[pvanv]

Re: tohatsu overheat senser still going off

Clean the cooling system and you will run a lot colder. That will likely fix your overheat problem.

 

[Sea Rider]

Re: tohatsu overheat senser still going off

If you like can clean piston heads by spraying OMC engine tunner spray, Sierra's carbon guard spray, letting soak for some minutes, brush off with an old toothbrush, repeat if needed, clean cylinder head as well, both crankcase and cyl head should be inmaculate clean of old gaskets residues, torque head gasket to specs, place new plugs well gapped and that engine should run fine as before...

If you go further removing crankcase from lower pan, need to buy a new base gasket. Slight grease upper drive shaft splines before inserting back crankcase to pan. Remove prop and grease well entire shaft too.

Happy Boating

 

[TOHATSU GURU]

Re: tohatsu overheat senser still going off

Well I took my cylinder head off this weekend and found alot of salt narrowed passages..I'm not sure what decarbon piston heads means??
I've went this far, should I pull the complete crank case off and inspect the lower crankcase??..That area from the outside,looking at the 8 bolts holding it on, looks dry and I guess deteorated more than the rest of the motor and foot..and i just looked at my pistons and they have a dark carbon look on their tops..

Get a tub, fill it with vinegar, run the engine for five minutes, stop for five minutes and repeat 10 or 20 times. It's a PITA, but better than pulling the block apart.

 

[realchuck63]

Re: tohatsu overheat senser still going off

I really appreciate all the good advise I've been getting from this form..It truly has helped me in locating
and repairing my M70C Tohatsu over-heating issues..

Thanks Guys

realchuck63