Tohatsu 3.5

[Stemar]

I have one of these engines, now in its 5th season. So far, as long as I treat it to a new plug from time to time, it's been brilliant.

On Saturday, it was dark and low tide when we got to the boat. As a result, I didn't realise as I left the pontoon, I was ploughing rather than sailing. I found out a few minutes later when the engine started to sound unwell and I realised that all that was coming from the little pee pipe was steam. Next day I cleaned the bunged up water inlet and all seemed to be well.

Now I've just run the engine in its dustbin in the garden to get the salt out, as I do regularly and there's practically no flow from the pee hole at idle. It improves as I rev up, but is very much dependant on engine speed - steady drip at idle and a stready flow at higher revs, where before, it always seemed to be the same.

I suspect gunge in the system, so here are the questions:

1. Is there a strainer in the innards?

2. If so, how do I get to it?

3. It's probably time I looked at the impellor. How do I get to it?

4. Is there a downloadable manual I can get hold of? (I have 2 left spanners, but can usually manage if I have a manual)

Thanks in advance!

 

[charles_reed]

Yes excellent engines even in Mercury and Mariner guise.

No there's no strainer as such.

Sounds as though your impeller has jumped off the cotter, get a new one from Fairweather Marine, then take out the rubber bung 2/3 of the way down the leg. Behind it you'll see the clamp for the drive/neutral dog clutch, unclamp that (preferably just the lower clamp).
Behind the change lever you'll just be able to see the drive shaft for the waterpump.

Undo the 2 x 10mm bolts just below the bung-hole and carefully take the drive leg apart (the waterpump drive shaft pulls out) if you haven't undone the change lever clamp enough it won't come apart. Don't use a screwdriver American or otherwise to get the leg to separate.
You'll now see tHe stainless waterpump (on the 2.5 it's alloy and the main cause of morbidity), undo the 2 x 8mm bolts and carefully separate, find inside one neoprene impeller in a state of collapse.
They seldom break up, but the drive groove wears when they try to pump semi-solids.

 

[Lakesailor]

Charles seems to have a different Tohatsu to me. Follow the instructions that seem to fit your motor.

It's unlikely that cleaning the pee hole will have any effect on the overheating. You can still have a proper cooling water flow in the motor even if the peehole is blocked. It is only an indicator of flow.
To get the impellor out take off the prop and remove the two bolts around the prop shaft. Pull the small plate off that the bolts fit through and there is the impellor. It just pulls out. If the tips are at all flattened or worn you need a new one. I expect after 5 years it's well due for renewal.

If that doesn't get cooling back to normal time to look inside the engine.

There is no strainer inside.

You need to to whip the head off and poke all the gunge out of the water jacket

and take the powerhead off the leg (you'll need a new gasket to reassemble) and poke out the waterways, particulalrly the holes that the water passes through from there to the cylinder waterjacket.

You may well break some studs that have become corroded in, so if you aren't confident you can drill them out get someone who is involved.

 

[charles_reed]

Curioser and curioser

if in doubt refer to the Tohatsu owners manual, available from here:

http://www.tohatsu.co.jp/en/boat/download/index.html

I changed the impeller on mine in April.

Unfortunately it's quite useless for stripping it but at least you'll know which one you've got.

 

[gandy]

Re: Curioser and curioser

I suspect the impeller location depends on whether the motor has a F/N gear or not.

 

[Stemar]

Re: Curioser and curioser

Thanks everyone. I spoke to Fairweather Marine, who reckon they can give the engine a full service and change the impellor for not a lot more than double what they'd charge me for the bits.

Given the aggro I always seem to have with things mechanical, that sounds rather tempting!

 

[charles_reed]

Very sound

folk, Fairweather Marine.

And they won't charge you silly money or do a c**p job.

I always carry a spare impeller, stainless (not bronze) shear pins and a spare tap for the tank.
Oh! I've had to change a prop once.

 

[VicS]

Re: Curioser and curioser

[ QUOTE ]
I suspect the impeller location depends on whether the motor has a F/N gear or not

[/ QUOTE ]

If it has a clutch (irrespective of whether it has F&R gears) the pump will be between gearcase and leg as first described. It can only be behind the prop on an engine (any make) if there is no clutch or there'll be no cooling when not engaged.

 

[Lakesailor]

Re: Curioser and curioser

Good point.
Mine is a very old one and hasn't a clutch or gears.

 

[Oldhand]

When I had the same lack of cooling water on a Mercury 3.3 (same basic engine) after exploring the River Yar and eventually found the Yarmouth (IOW) agent to get a new impeller, they advised me to blow air through the system before going for an impeller change. I thus attached a car tyre foot pump to the cooling water tell-tale outlet on the motor head after removing the existing short tube. After some furious air pumping, pump was removed, short tube replaced and when the engine was run, flow from the tell-tale was back to normal and has been ever since.

I would thus always recommend the above procedure as a first step.

 

[chrishelen]

Hi i was once told you cant get a true flow of cooling water if you use a dustbin cause of cavitation,might be something in it.Too much air bubbles kicking about.

 

[VicS]

[ QUOTE ]
Hi i was once told you cant get a true flow of cooling water if you use a dustbin cause of cavitation

[/ QUOTE ] Yes that is often said (I don't have any problems using an old plasic coldwater storage tank) The solution is to take the prop off!

 

[srp]

Or, in the case of a Tohatsu 3.5, put it in neutral (where's that 'smug' smiley???).

 

[chrishelen]

Hey thats a good idea,but dont the bubbles from the exaust cause probs?

 

[Stemar]

As I write, Ol' Faithful is sitting in a dustbin of water in my garden, feeling much better for a clean out and new impellor. I really believe that a fresh water run every time I come home is the best thing I can do for her.

I decided to go professional, 'cos I my annual service consists of a new plug and a bit of grease and at 5 years old, I reckoned that the impellor was probably tired.

Full marks for Fairweather Marine, who took it in on Friday at 1000 and had it ready by 1500, with only a day's notice. Full service, impellor and new knobs on throttle & choke for just over £80. The bits would have cost me close to half of that and I'd have spent all weekend swearing at it instead of going sailing.