3.5 hp Tohatsu 2 cycle not pumping water - SailNet Community
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post #1 of 12 Old 09-02-2009 Thread Starter
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3.5 hp Tohatsu 2 cycle not pumping water

I have a 1993 3.5 hp Tohatsu 2 cycle on my P15 Potter sailboat. It runs great but it is not pumping cooling water ( not coming out of the drain line when the engine is running)

Without the cooling water I'm afraid I'll ruin the motor and I checked and it doesn't look like I have any blockage on the water intake.

What do I need to do to check out the pump mechanism in the motor. he manual says take in for service. The motor is only valued at $50 on the market and I just replaced the spark plug and coil which was $60. They dried out from old age.
I noticed the pump wasn't working when I had the motor in trash can full of clean water testing it with the new spark plug and coil.

The motor has very few hours on it since it's only used to motor away from the dock when we take the boat sailing.

I don't want to dismantle the motor if it's something easy to test or clear. The boat has only and motor have only been in fresh water.

Last edited by jsmithsussex; 09-02-2009 at 12:56 PM. Reason: typos and clarification
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post #2 of 12 Old 09-02-2009 Thread Starter
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if the motor can't be repaired?

Whats the thrust on this motor because I'd probable go to an electric trolling motor as a replacement?
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post #3 of 12 Old 09-02-2009
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When you say it isn't pumping I assume you mean you can't see any water "pissing" out the telltale at the back of the motor? All that is is an indicator, a sidestream tell. These are small holes that often plug up with salt or whatever.

Try reaming the telltale out with a small wire. There may well still be cooling water flow OK, just that indicator stream may be plugged.

Since it's running great it doesn't sound like you're overheating....

btw - we own the Nissan version of this motor.. I sure hope it's worth more than $50!

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post #4 of 12 Old 09-02-2009
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Sounds like the impeller. These require periodic replacement. Go here:

Nissan Parts - Nissan Marine Outboard Parts

This assumes, of course, that you are not clogged up. But if you are not making water off the back and nothing has come out for a while, you may have already burnt up the impeller.

I also doubt the $50 aspect of that motor. Maybe if it is a POS and not working, but certainly it is worht more than that. Many of the parts alone would be worth more than 50 bucks. You will see that shortly.

As Fast said, it might make sense to check for a cloggd input/output too. But if you have not replaced the impeller and have had it for a while, that may be your issue.

BTW, Faster, I think Tohatsu makes the engines for the Nissan. I also think they make it for Mercury and Yamaha under 9.9. You probably already knew that though.

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post #5 of 12 Old 09-02-2009
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IF its a freshwater motor it should be EASY to service the waterpump and if you dont how old it is its to old

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post #6 of 12 Old 09-03-2009
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My ancient Yamaha 2 hp, which is similar, had the same problem. First step, esp for a freshwater engine, is to check the condition of the water pump impeller, which is not that difficult to get to. After replacing mine, I still had a problem, which ended up being a cooling jacket around the piston that was completely salt encrusted. It was fairly simple to pop off the head, clean out the cooling jacket with a screw driver, replace the inexpensive head gasket and reassemble. It has run like a top ever since.

Even in top performance, I believe it is a more accurate description to say the cooling water for these little motors "spits" out rather than "pisses" out in a steady stream like it does in larger outboards.
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post #7 of 12 Old 09-04-2009 Thread Starter
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Thanks everyone for the responses

The motor is the original 1992 2-cycle motor.

The motor runs fines still. I rarely running more than a few minutes. I observed that it wasn't spitting water because I was testing the engine after I did a carburator clean up. I love the motor. The $50 value is the NADA value for a 1992 Tohatsu. Truth is it's worth a lot more to me than $50. That's why I don't want to ruin the engine because it doesn't have cooling water flowing.

I went back to the part site and found the exploded view and pretty comfortable that I can disassemble and replace the impeller if that's the problem.

Last edited by jsmithsussex; 09-04-2009 at 03:37 PM. Reason: typo
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post #8 of 12 Old 09-05-2009
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Don't run it until you fix the cooling water problem! Chances are it's either the impeller or clogged cooling passages. An inexpensive fix either way.
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post #9 of 12 Old 09-06-2009
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If you really do care about this motor I have a suggestion. After replacing the impeller go buy a gallon or two of vinegar. Replace the water in your test bucket with the vinegar and run the engine for a while. This will clear up the cooling passageways. I have the exact same model and it "pisses" a solid stream, so yours probably should too.
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post #10 of 12 Old 09-06-2009
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Before you replace anything, do what Faster suggested. If that doesn't fix it, find the hose that runs from the powerhead to the pee hole; it may be clogged. I had this same problem on my outboard (different model but 1990). Clearing the pee hole didn't help, but there was an obstruction in the hose a couple of inches upstream.

If your cooling system really is broken your motor should have destroyed itself along time ago.

That said, if you have had the boat for a while and have never changed the impeller, you probably should do that anyway. Just make sure that your diagnostic procedure checks the simplest thing first.

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