Tohatsu 3.5 2 stroke outboard - impeller question.

[peter2407]

Looking at servicing the above, so downloaded the user manual. There is no reference to there being an impeller. Am i being thick? I expected all outboards and marine engines that are water cooled to have an impeller?

 

[rosssavage]

Is that the rebadged mariner 3.3 2t?

If so, the impeller is located at the bottom of the leg and is driven by the driveshaft. Take the lower gearbox off, undo the impeller housing (pressed steel thing) and slide the impeller all the way up the driveshaft to remove it. DO NOT pull the driveshaft out - the bevel gear falls off the end in the gearbox, requiring gearbox disassembly to recover and refit. Ask me how I know

The impeller is "locked" to the driveshaft by a loose floating steel pin. Tiny and super droppable, be careful you don't lose it when you slide the impeller up. Done mine twice now - not difficult, but a bit fiddly. Hardest bit is lining up driveshaft, water pick up and gear elector when refitting gearbox. You need a minimum of three hands!!

 

[30boat]

My 2,5 Mercury has the impeller in the same place.All I needed to do was to take the prop out remove a plate and the impeller could be removed.
http://www.crowleymarine.com/mercury-outboard/parts/11761_100.cfm

 

[VicS]

If the engine has fnr gears or even just forward and neutral the water pump will be located on the top of the gearbox and driven by the vertical shaft necessitating removal of the gearbox to renew the impeller.

If the engine has a fixed drive the water pump may driven by the prop shaft and located behind the prop. More likely to be so in recent models although older engines more likely to have it as above.

This diagram shows the location in a Tohatsu 3.5 2stroke, on the prop shaft

http://www.boats.net/parts/search/T...USING, GEAR CASE & STEERING HANDLE/parts.html

 

[peter2407]

Thanks all. Lazy git questions - is replacing the impeller worth the aggro if the water flow is consistent? Plus, the manual says force the gear oil in from the bottom. I dont have z squeezy thing so can i pour itfrom the top?

 

[rob2]

My old Tohatsu 3.5 has the pump on the top of the gearbox, so you have to drop the leg to access it. Assuming all the screws come out easily, it's not so difficult, but reattaching the leg and getting the ecxhaust, gear shift and drive shaft all in at the same time can make you weep for a few minutes. Many engines run for years without changing the impeller, so long as the flow is good. Even then, usually the first reduction in flow is caused by salt encrustation inside the piddle hole under the power head, pull the rubber hose off and poke around a bit to clear it before going to the trouble of stripping the leg to inspect the impeller! All written from the experience of changing the impeller before finding the salt crystals...

In case you feel you need it, I could be persuaded to lend you the workshop manual on CD. PM me if you want it, although most things I would be happy to undertake don't really need it.

Rob.

P.S. I think filling from the bottom of the gearbox is to ensure you don't think it full when a airlock holds the oil in the top half. I'd be happy to add the correct measure amount from the top and wait for it to find its way down before starting.

 

[VicS]

Thanks all. Lazy git questions - is replacing the impeller worth the aggro if the water flow is consistent? Plus, the manual says force the gear oil in from the bottom. I dont have z squeezy thing so can i pour itfrom the top?

If the water flow is Ok there is not a lot of point in changing the impeller except you dont want to leave it until it's not or the impeller breaks up. Not a major job when its located behind the prop. Much more aggro when you have to remove the gear box to get at it.

Filling from the bottom upwards ensures its full with no air locks. It's very difficult to get oil in and allow air to vent through the same small hole although I have brass syringe, like a giant hypodermic syringe, that I sometimes use. The oil is usually supplied in squeezable tubes anyway

 

[30boat]

My 1990 Mercury was given to me and the impeller was still all there but was beginning to break up.They're cheap enough,I'd replace it.As for the oil you can use a large feeding syringe.I've just changed the oil on my BMW bike and used one.It cost me 1,4€ at the chemist.

 

[jwilson]

My old Tohatsu 3.5 ...... reattaching the leg and getting the exhaust, gear shift and drive shaft all in at the same time can make you weep for a few minutes......

Maybe more than a few minutes. It's the sort of job that's easy if you have three very tiny hands and X-ray vision - you are working through a small hole in the leg behind the rubber bung.

 

[HRay]

I'm new here and this thread has exactly the information I'm looking for, HOWEVER, when I removed the lower unit the drive shaft stayed in the engine rather than coming off with the lower unit. I have tried to get it out by clamping onto the splines at the lower end (with leather protection so as not to damage them) and tapping with a mallet but no luck. I cannot get the shaft to move at all. Any suggestions? Thanks!

 

[alan1954]

Hi,

Guess what? The driveshaft was seized at the upper end, and so the lower end pulled out when I removed the gearbox. Now it won't go together fully so I guess I have dislodged the bevel gear like you did.

To save a lot of trial and error, how did you sort the problem? Thanks,

Is that the rebadged mariner 3.3 2t?

If so, the impeller is located at the bottom of the leg and is driven by the driveshaft. Take the lower gearbox off, undo the impeller housing (pressed steel thing) and slide the impeller all the way up the driveshaft to remove it. DO NOT pull the driveshaft out - the bevel gear falls off the end in the gearbox, requiring gearbox disassembly to recover and refit. Ask me how I know

The impeller is "locked" to the driveshaft by a loose floating steel pin. Tiny and super droppable, be careful you don't lose it when you slide the impeller up. Done mine twice now - not difficult, but a bit fiddly. Hardest bit is lining up driveshaft, water pick up and gear elector when refitting gearbox. You need a minimum of three hands!!

 

[ZorbaTheLeek]

Just done the job on my Tohatsu 3.5 2T as a dribble from telltale warranted further investigation, so few comments to add to the above

When the impellor was removed from the drive shaft the small float pin was missing. Looked everywhere but found him hiding at the bottom of the leg so had to remove the stainless cover and upend the leg for the pin to fall out so that's where they live when not at home. Re-assembled with a slight improvement on tel tale flow. Picked up what rob2 said above about the piddle hole
"salt encrustation inside the piddle hole under the powerhead, pull the rubber hose off and poke around a bit to clear it"
The powerhead discharge is ridiculously small so any salt will impede flow. I gave a spray of de-greaser and that cleared the restriction with 100% improvement on flow so telltale flow is now back to full when on idle.
Thankfully I have three hands

 

[ChromeDome]

Tohatsu is the mother of most small outboards, so similar regardless of brand.

 

[QBhoy]

Is that the rebadged mariner 3.3 2t?

If so, the impeller is located at the bottom of the leg and is driven by the driveshaft. Take the lower gearbox off, undo the impeller housing (pressed steel thing) and slide the impeller all the way up the driveshaft to remove it. DO NOT pull the driveshaft out - the bevel gear falls off the end in the gearbox, requiring gearbox disassembly to recover and refit. Ask me how I know

The impeller is "locked" to the driveshaft by a loose floating steel pin. Tiny and super droppable, be careful you don't lose it when you slide the impeller up. Done mine twice now - not difficult, but a bit fiddly. Hardest bit is lining up driveshaft, water pick up and gear elector when refitting gearbox. You need a minimum of three hands!!

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