07 Tohatsu 3.5 4stroke...overheating?

[urbanredneck]

Good day yall.

So long story short, ive got a new to me 2007 Tohatsu 3.5hp 4 stroke long shaft tiller. Seemed to run fine at time of purchase, but the man had limited time so I checked compression and all the obvious and purchased it. From what I was TOLD, this motor was a dock navigator on the back of a sail boat in fresh water.
Now, im not too familiar with small outboards. What im experiencing may be normal, but I have no close by dealer to ask.

My concerns are that its overheating. I have a strong tell tale. However, the temp of the discharge water is only about ~5 degrees warmer than the intake water in the bucket. The mid leg and head seem hot to me. My temp probe got about ~150*F at the head under the spark plug. Harder to reach areas were too hot to touch for long.
Just removed the thermostat and confirmed its operation. Opened around 135, slowly closed when I removed it from the pot.

Do these values sound ok? Am I overthinking it? Anything im missing?

Only other areas of concern that Im unsure are related, spark plug had a bit more oil on it than id like to see when purchased, and the RPM tend to surge up and down slightly while in neutral in idle.

Other than that it runs just fine. Starts 1st pull, No stalling, always pumping water, shifts great. Just looking for some insight.

Thanks everyone

 

[raczekp1]

what temp is runing your car( its 4stroke also) ? and why so high?

 

[urbanredneck]

what temp is runing your car( its 4stroke also) ? and why so high?

Currently my oil temperature in my Subaru is 142. I've just always been told if your outboard is too hot to the touch, there could be something wrong

 

[km1125]

"Too hot to touch" is about 120F, which would be very low for most outboards. Your thermostat was 135F, so I would expect something around that, but probably 140-145F. Would not be concerned unless you were measuring over 180, but seeing 160-170 would say that there's something that needs to be investigated.

 

[urbanredneck]

"Too hot to touch" is about 120F, which would be very low for most outboards. Your thermostat was 135F, so I would expect something around that, but probably 140-145F. Would not be concerned unless you were measuring over 180, but seeing 160-170 would say that there's something that needs to be investigated.

Thanks for the reply. I may invest in an IR gun. Was using a multimeter with a temp probe when getting my measurements. Requires taping the end of the wire to an area to get a reading and this engine is tiny.

But with everything being said, and everything thats been verified, if i do experience temps climbing above ~170, whats next? Pulling the head and checking the passages?

 

[pvanv]

Anything around 150F is fine. When was the last time the wp kit was done? If run in salt and not flushed regularly could have buildum in the head areas.

 

[urbanredneck]

Anything around 150F is fine. When was the last time the wp kit was done? If run in salt and not flushed regularly could have buildum in the head areas.

Im unsure when the last WP service was done. It does pee quiet strongly. But from what ive learned that isnt always just OK

 

[km1125]

Thanks for the reply. I may invest in an IR gun. Was using a multimeter with a temp probe when getting my measurements. Requires taping the end of the wire to an area to get a reading and this engine is tiny.

But with everything being said, and everything thats been verified, if i do experience temps climbing above ~170, whats next? Pulling the head and checking the passages?

If you started seeing temps >170, then you might have some buildup or debris in the passages as Paul mentions. Was this a salt water engine? What did it look like inside when you pulled the thermostat?

I'm not sure on the 3.5 engine, but on the 4, 5 and 6hp motors the pee stream is before the water enters the engine. You could actually plug the pee stream and it would force more water through the engine (provided the thermostat was open), but then you'd lose that visual indicator.

You won't get a completely uniform temperature all over the motor when you check. There will certainly be areas that are hotter and areas that are cooler, so don't be shocked or worried if you can find one little area that hits 170.

 

[urbanredneck]

If you started seeing temps >170, then you might have some buildup or debris in the passages as Paul mentions. Was this a salt water engine? What did it look like inside when you pulled the thermostat?

I'm not sure on the 3.5 engine, but on the 4, 5 and 6hp motors the pee stream is before the water enters the engine. You could actually plug the pee stream and it would force more water through the engine (provided the thermostat was open), but then you'd lose that visual indicator.

You won't get a completely uniform temperature all over the motor when you check. There will certainly be areas that are hotter and areas that are cooler, so don't be shocked or worried if you can find one little area that hits 170.

Right on thanks.
I am also uncertain of the path the cooling water takes in this engine. Could only find service manual for 4hp and up and those didnt provide too much information.

I was told this was a freshwater engine. No exterior evidence of salt/corrosion.

The chamber in which the thermostat sat in was a bit mucky....nothing that looked like mineral deposits. More like a slight tan film one may find in a carburetor. I cleaned that out.
I just really want to avoid pulling off the head for obvious reasons. I guess at this point ill just run it lightly until i purchase an IR thermometer.

Anything else I can do, anything to watch out for; something I may notice happen if the engine does overheat while on the water? Again, not used to these small engines that dont have gauges, warning signals, etc.


Thanks again

 

[MattFL]

If it was a freshwater engine, the thermostat is good and the water pump is in good condition, then odds are you're fine. Four strokes run hotter than 2 strokes so if your reference was an old 2 stroke then that's not a good comparison.

 

[Sea Rider]

If assuming the motor is overheating due to water paths are clogged or with less diam than factory delivered, get a flushing adapter available from Tohatsu, remove the water plug (bolt) located under the powerhead, screw the adapter there and flush the motor with a hose as long as you want. Remove the thermo, put lid back on before prior flushing to flush all the water passages...

It's a very bad idea to measure the temp of any motor while runs in a bucket, you can't possibly cool the motor with same amount of heated water cycling around the bucket, for that need a fresh amount of water pouring in and lower bucket's heated water going out as to renew the water cooling the powerhead, Or measure the temp with a heat gun while the motor runs at wide open throttle at open waters....​

Happy Boating

 

[urbanredneck]

If assuming the motor is overheating due to water paths are clogged or with less diam than factory delivered, get a flushing adapter available from Tohatsu, remove the water plug (bolt) located under the powerhead, screw the adapter there and flush the motor with a hose as long as you want. Remove the thermo, put lid back on before prior flushing to flush all the water passages...

It's a very bad idea to measure the temp of any motor while runs in a bucket, you can't possibly cool the motor with same amount of heated water cycling around the bucket, for that need a fresh amount of water pouring in and lower bucket's heated water going out as to renew the water cooling the powerhead, Or measure the temp with a heat gun while the motor runs at wide open throttle at open waters....​

Happy Boating

I did in fact take that into account. I had a nice cool water supply running into the bucket to offset any heated water and/or exhaust below the waterline.
Ill look into getting a flush plug adaptor. Wish I had a local dealer...

Thanks for your commentary.

 

[pvanv]

FRESHWATER FLUSHING PLUG (2HP~30HP 4STR / 4B~40C 2STR)​

Description
Attaches hose to motor in order to flush motor with freshwater after use in saltwater and/or brackish water.

Fits 4B ~ 40C 2-stroke models & 2hp ~ 30hp 4-stroke models.
Part #: 336600070M
List Price (MSRP): $8.10

 

[Sea Rider]

What like about Tohatsu motors is that small 3.5-5 HP portable range models counts with a flushing port (large bolt) located under the crankcase, connect the flushing adapter seen on previous post attached with a garden water hose. Flush with motor running at idle /fast idle for thermo "to open" up and flush the cylinder head area as long as you want. If counting with high water pressure much better.

Happy Boating​