Help! Tohatsu 70 HP M70A2 Overheating

[Petedacook]

Well, I changed the heat sensor and it stopped sounding off at low RPM. I also adjusted oil ratio and ran it 40:1 instead of 50:1. With the 40:1 mixture I ran it hard full throttle for a couple hours. After a the couple hours full throttle, the heat sensor started going off.

I am not sure if the overheating is related to the oil ratio, but I am going back to 50:1 ratio. I am going out this weekend and will see how it does.


The reason I changed the oil ratio was because the book says to run 50:1 only if using Tohatsu oil, and use 20:1 if any oil other than Tohatsu is used.

 

[Sea Rider]

If that's a pre mix engine version 50:1 is the way to go no matter which 2 strokes brand it's used. ideal for wot runs at extended time period. Will foul plugs way less when at idlel/fast idle speeds. At 20:1 engine will smoke worst than a gang of chinesse poker players and definitely will foul plugs prematurely.

Happy Boating

 

[Petedacook]

I think I have figured this out. I think it is the impeller liner. I used the toothpate method, but grooves still got caught in fingernail after 12+ hours.

So i put everything back together and have gotten the heat warning sound mentioned above since putting the new impeller in.

I took out the new impeller (less than 30 hours on it I would guess) and it has deep groves in it from the impeller liner. Also, I found out I toasted the impeller by using petroleum based product when installing the new insert.

So.......I ordered a new impeller (on it's way). Then I took the impeller liner out and used rubbing compound to get the groves out of it so I cou ld not find them with my fingernail.

I put the old impeller back together with the newly re-scrubbed impeller liner. Took it out for a few hours Friday & Saturday at various throttle positions and no overheat sensor.

I need an impeller liner. I've been looking everywhere and cannot find one. Im gonna make a post for an impeller just in case someone has one on a junk engine in the back yard or something.

Thanks,

Pete

 

[Sea Rider]

Pete,

Liner should feel smooth even to fingertip when rubbed, if there are lines that can be felt with fingernail your's is very worn out. Polishing too much will vary its internal diam and impeller will pump with less pressure. You could have an associated water hidden isssue, say lower and upper water grommets are not sealing tight both water tube extremes and loosing water & pressure, even having a corroded water tube somewhere ? Dip new impeller and liner housing with soappy water, reinstall.

Are all water passages clean ? Immaculate clean water passages will dispel faster heat build-ups inside crankcase and combustion chambers, engine will work top at its correct working temp.

Happy Boating

 

[Petedacook]

Circling back to inform any future internet surfers. I took the rubbing compound to the impeller insert, got it smooth and replaced the impeller that was formally new with a new impeller. I have taken the boat out 3-4 times for 8 hour session without an overheat issue. For now the rubbing compound and new impeller seems to have done the trick. Too bad the season is over, or seems to be over in my area.....it's getting cold here in Virginia.

Second note; I got wind of Karbonwerx, Scott, on Facebook. I ordered an impeller and housing from which came with gasket and water line grommet. The parts arrived today, 10/6/15, and they look awesome. Scott was great to deal with and provided very professional service and super high quality looking product. I will not be using the product until my current insert impeller combo goes out, but at least I have it and it looks outstanding!

Big thanks to everyone here for your help, and huge thanks to Karbonwerx, Scott, for an awesome product and an awesome price.

 

[philipp10]

Send me an email when you get this. I have a source in Florida. They part these motors out all the time and have lots of parts. philip.poeschl@tsi.com

 

[Chovus]

Pull lower leg and insert a wate hose on thermo hole and give a high water pressure flush for 5 minutes, will remove any crude, debris located on any water passages. Latter check impeller cond, change complete WP kit if previos owner was boating on sandy, muddy waters as impeller liner will be excesively abraded.

Hello frinds. Similar problem. My first post on this forum.

I am newbie and my English is bad (not horible). What do you mean lower leg? Do you mean gear unit?

Can I skip that step, and flush a vinegar through thermostat hole (bottom hole) for five minutes (1L in loop) and then flush with fresh water and strong pressure?
Or maybe use "air compressor" first through nipple pipe (last hose, where water is coming out) and try to debrie stucked somehow move a little?

I already try new sparks (1mm).
I put a 1/2 smaller propeler, didnt help either.
I checked thermostast and it opens 6mm (0.24"), didnt now that I need to watch temp but I think 65 'C start opening. I will check in few hours (night is here).
I will try to lower my outboard for one hole, first, down to trensom. Now is maybe a 7mm lower than boat line.

Thanks in advance
My outboard is M70C
Boat is Saver Open 540

 

[Naddaman]

I got the impeller, impeller key, and thermostat and thermo gasket after doing some intense internet searches. I began looking for part numbers rather than motor name & part needed. I got better results this way.

I put the bottom end back together and the thermostat in with new gasket. Fired it up, ran good, throttled it up on the muffs hanging out my garage in a town house, sounded good, ran good, buzz from overheat went away, temperature felt good (I dont have infrared temp gauge).

Cam inside, wife asked me WTf is wrong with me. It's 11:00 at night and I am firing up the neighborhood. I was so into my work, I lost track of time and was inconsiderate to my neighbors.

Any how, I used toothpaste and worn green scrubby to remove grooves in the impeller housing. Put everything together; grease on WP bolts, housing bolts, pump inlet, drive shaft spline, and all looks and sounds great,

Many thanks to Sea Rider. Appreciate the tips and advice along the way. And they were a big help.

Pete

Hoping you are still active, Bc I recently picked up a boat in great condition and motor is very clean. I replaced impeller bc it was chewed away not as good as yours , mine was missing half of the fins,
I have removed thermo completely and ran it still get the buzzing for overheat, its pissin really boiling hot though. Not sure what to do next. Please someone help me keep this boat alive!!!.