Tohatsu 3.5 Outboard - 2 stroke

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McPhail the Engineer

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Our Tohatsu 3.5 outboard ( bought in 2003) is very lightly used and was most recently professionally serviced in 2023. When we tried to use her this season she started without too much difficulty but the cooling water was dribbling out from the rubber tube rather than flowing steadily. I was advised that there might be a build up of salt since she hadn't been run in fresh water since the back end last season. I have tried to clear any blockage initially with a long paper clip but since there was no improvement. I brought it home stripped it down and straightened the tube to try to clear it with a long thin knitting needle.

I have not had the opportunity to test it yet but does anyone have any suggestions as to where to turn if it doesn't work any better. :unsure:
 
Test and see if that works

Run it in a bucket of fresh water and see if that clears it. Might be an easy fix. Keep changing the water. Try a bucket of hot, but not boiling, water maybe?

Running fresh water is less intrusive than poking in a wire and may work better as it'll run through all the little channels you can't get to.

I usually run the o/b in a bucket of fresh water after using it in sea water

You can by a hose attachment to run fresh water through straight from a tap.
 

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There are various chemicals you can add to water to run through the engine ... I like the one used for Central Heating boilers / systems ... you can get for Alloy and Iron use ... so no problem for your engine (use the version for Alloy) ...

There's Rydlym ....

plus others ...

Once waterways are clear - then good run flushing in clean fresh water to remove the chemical.
 
PabloPicasso said:
You can by a hose attachment to run fresh water through straight from a tap.
Click to expand...
The "muffs" in your link are not suitable for many small outboards. The are only suitable if the water intakes are on the sides of the lower unit and the muffs seal on to it.
Some small outboards have provision to screw a hose connector directly into the cooling system.
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McPhail the Engineer said:
Our Tohatsu 3.5 outboard ( bought in 2003) is very lightly used and was most recently professionally serviced in 2023. When we tried to use her this season she started without too much difficulty but the cooling water was dribbling out from the rubber tube rather than flowing steadily. I was advised that there might be a build up of salt since she hadn't been run in fresh water since the back end last season. I have tried to clear any blockage initially with a long paper clip but since there was no improvement. I brought it home stripped it down and straightened the tube to try to clear it with a long thin knitting needle.

I have not had the opportunity to test it yet but does anyone have any suggestions as to where to turn if it doesn't work any better. :unsure:
Click to expand...
Lots of good advice.

Remember the dribble is coming from a telltale hole. Clearing that does NOT prove that the entire engine is getting good flow. Also, if the bit that comes out is black it is probably an impellor chunk. The rest of the damaged impellor may be stuck other places, not so easy to get to.
 
thinwater said:
Lots of good advice.

Remember the dribble is coming from a telltale hole. Clearing that does NOT prove that the entire engine is getting good flow. Also, if the bit that comes out is black it is probably an impellor chunk. The rest of the damaged impellor may be stuck other places, not so easy to get to.
Click to expand...

What does "professionally serviced" mean? Ask for details. If it is a plug, some lubrication, and a shot of carb cleaner ... they kind of took your money. Or rather there is no reason to believe they replaced the impellor.
 
I had Fairweather Marine at Fareham service mine. Over £100 but it's extremely reassuring to know there's a new impellor, hub lube, etc.

Vyv Cox's cut-fender is brilliant because it doesn't need a water tank or stand - the engine can even be flushed while still on the transom.

Without a broken fender of my own I repurposed a damaged buoyancy tank. I thickened the fabric with gorilla tape and used plastic grommets.

The thing rolls up small but has space (just) for the Tohatsu 3.5's leg. Just make sure it's in neutral before starting the engine.


I recognise that the telltale on its own is not proof that the cooling channels are perfect, but it has to be better than no visible flow.

I suppose it takes 15 or 20 litres of fresh water to immerse the leg as required. That may seem a lot while cruising a small boat remotely but knowing the engine is properly rinsed internally is well worth it and I never let it go cold without freshwater flushing.
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andsarkit said:
You should find a bolt under the engine which is removed to fit a flushing plug for a hosepipe.
Click to expand...

😧 How is it possible that I've read dozens of threads on flushing small outboards, and this is the first I've heard of such a fitting on my own?

I must learn to read the manual.

53949546746_929030e0cd_z.jpg


Bobc said:
I blow mine through with an airline. Seems to sort it.
Click to expand...
D'you mean mine, or did you succumb and buy another? ;)
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We run ours for five minutes in a five gallon brewing bin filled with fresh water at the end of each week of use.
Obviously in neutral 😐
 
dancrane said:
😧 How is it possible that I've read dozens of threads on flushing small outboards, and this is the first I've heard of such a fitting on my own?

I must learn to read the manual.

53949546746_929030e0cd_z.jpg



D'you mean mine, or did you succumb and buy another? ;)
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Click to expand...
I bought another one. Should never have sold that one to you. The 4 stroke was just way too heavy.
 
Ive had my tohatsu from new. I flushed it every time after use. After many years the tell tail reduced dramatically.
I popped the head off and was surprised to see how full of salt the water jacket was around the cylinder head. I'm amazed any water got through at all.
Raked out the deposits, popped the head back on. So easy to do.
Now i dont bother flushing at all as its easy to clear it out again.
My theory is that once you stop the engine the heat from the cylinder evaporates the remaining sea water leaving the deposits before you get to running it in fresh water so why bother?
It was many years ago i cleaned it and it still has a good stream from the tell tail.
 
dancrane said:
😧 How is it possible that I've read dozens of threads on flushing small outboards, and this is the first I've heard of such a fitting on my own?

I must learn to read the manual.

53949546746_929030e0cd_z.jpg



D'you mean mine, or did you succumb and buy another? ;)
.
Click to expand...

Wait, there's a flushing bracket for a Tohatsu 3.5 2T?

Why do you need to remove the prop? Seems needless? Just safety in case you knock it into gear?

Is the part number ENOF02040-0? I can't find it online?

Game changer.

Anyone know do the Mariner 4/5hp 2T have similar?
 
It's all new to me, too...if anyone knows, please chip in.

Andsarkit's video in post 10 seems to show the operation clearly, and I've found the bolt on my 3.5...

...although the stream looks pretty weak from the telltale, assuming there is the usual domestic head of pressure in the hose.

I too wondered why it would be necessary to take off the prop. :confused:
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