Tohatsu 3.5A overheating

[imagineero]

I recently received an ancient 3.5A together with a sailing dinghy I bought, both are in good order and appear to have been well taken care of by the original owner who purchased them both new many moons ago. The outboard was a little recalcitrant but drained the tank, stripped the carb and popped it in an ultrasonic cleaner, new plug and she fired up first pull. Popped a new 3 blade prop on her and had plenty of power for the small dinghy but she seems to have an overheating problem. So far I'm into it for about $20 with the prop and plug. Pulled the impeller and it's in good order.

Piddle pipe keeps getting clogged, cleaned it out a bunch of times with wire and tried a suitable size drill bit but she kept clogging within minutes. Finally pulled the head and the water passages were well filled with salt. Managed to get the head completely submerged in the ultrasonic cleaner and had it in there for about an hour came up very clean. Put it back together and popped a hose on the inlet pipe with lower unit removed and confirmed good strong flow now.

Seems to me that the piddle pipe is the only way water can leave the system though? I would have thought the tell tale was just that and there would be a water discharge out to the exhaust since the tell tale is so small and likely to get clogged easily. If there is a discharge it must be well clogged because with the garden hose on the intake pipe the only place water is coming out is the tell tale. Is it the case that this is the only discharge, or is there a discharge somewhere else that is clogged? Couldn't see anything obvious inside the powerhead but it's so small and could have easily escaped inspection. Didn't find mention of a discharge in the service manual or anywhere on the net. Is there a thermostat on these smaller outboards somewhere? All help appreciated.

Shaun

 

[Sea Rider]

Welcome to Iboats,

If you desalted the cylinder head you should have done same on entire powerhead. How do you know is overheating ? What you can do is put OB on a barrel and flush engine ON with a mixture of 70% water, 30% vinegar, use Salt Away.

Under lower power head there's a bolt, remove it and flush OB off straight with garden hose attached to a high pressure port, will need to buy flusher adapter. If using will see that water is also discharged from prop exhaust.

If small peeing port can't be cleared, remove both plastic side covers, detach small rubber hose from powerhead, let red cannula in and spray an overdose of W40 into port, let soak for some minutes, re install hose and start OB on barrel..

Happy Boating

 

[pvanv]

Yes. The majority of cooling water goes out with the exhaust. If not, you still have a clog. The lower flush plug may help you clear it out. The A series impeller and cup (head) can be tricky, and do not pump as well as the B models. A new impeller every year or so is always a good idea.

 

[motretu]

when you had the head off and de-salted, did you also clean out the water passaged around the cylinder? if yes, and coolant is not being spit out the down column just above the water line, then my experience is that the bottom plate to which the power head attaches and which provides the cooling water exit path to the exhaust stream, is likely clogged with salt like the head was. unfortunately, the only way i've found to clear such a clog is to remove the power head from the plate. not difficult if the six attachment bolts come out without shearing.

 

[Sea Rider]

To clean any salt obstruction if assuming there's more left inside OB you can :

-Flush OB on a barrel with 50% water, 50% pure vinegar of your brand prefference.
-Use Salt Away Products, follow instructions.
-Buy a Tohatsu adapter, remove large bolt under powerhead, connect a garden hose with high pressure and flush as needed.
-Connect the water jet output of a Karcher Washing Machine set al low pressure on that flushing port.

If you remove powerhead from pan, will need to buy a new base gasket..

BTW, lower powerheads of 3.5 & 5 HP OB's can be felt extremely hot if finger touched while OB is runnning for some time, but ain't an overheat cond, when you do have one, gear lever will turn extremely hard to shift forward/reverse till OB cools down. OB performance will be lousy when opening throttle past idle/fast idle.

Happy Boating