Dinghy Seatrial fail

[sanibel sailor]

Bought a used inflatable 8 years ago, like new, I have not had much need to use it, so it has been in storage.
Also picked up a Nissan 5 horse 2 stroke outboard to go along with it. Last ran it in 2013.
Am planning a trip up the coast where I am likely to need it, so I better get this gear out and check it over. Dink had a couple spots needing some glue, quick fix. Nissan was troublesome. The outflow tube from the integral tank had broken, no easy fix, so new tank. With that, it started right up. No water coming out- and that impeller was new just 7 years ago!
Put in new impeller. Just a trickle of water out check port. I look thru the service manual and don't see a thermostat or anything else that could be a problem Stuck a thin wire up the pee hole a couple of times (cringe) and that seemed to restore a good stream.


Now it revs nicely, goes into gear well enough to empty the bucket, seems to be cooling, ready for sea trials. I am wondering if this old Nissan will have enough power to get me up on plane.
Assemble and inflate the dink, careful not to overinflate as it is blazing hot sun today, down to ramp and launch. Remembered my PFD, type 4 and whistle.
Launched and it fired right up. I am kind of surprised. Puttered around the no-wake-zone cove a bit, seems to run OK, so I head for open water. In chop I realize it is still a bit underinflated, but responds wellto throttle and gets up on plane. All seems well. I slow down and check that water is still coming out the check port- all OK.


I get a little more adventurous, trying to get a bit away from the confused motorboat chop in the channel. She running good. I am loving the two stroke power, simplicity and reliability. Until it just slows down and dies. No catastrophic noise, no smell, just stopped. I try the pull start cord and cannot get it to turn over at all.



The problem is obvious to me. Even with the new impeller, there was not enough cooling water (as shown by the earlier dribble from the check port) and now this thing has overheated and seized. I start rowing back. I quickly appreciate that I am much further from the ramp than I seemed to be just a few minutes ago. The dink is underinflated which makes rowing more of a chore. Fortunately for this imperiled mariner, a powerboater takes pity on me and tows me back to the ramp.


Loaded back in the truck and driving home, I was a bit despondent over the motor's demise, wasted money on the new tank and my future need to rebuild it, are parts even available, how bad is the cylinder bore, etc. I suddenly recall the passage in the service manual where is says not to disable the start-in-gear protection mechanism... Doh!



Sure enough, back home, in neutral now, pulls easy and starts right up. When I sort out the cause of its abrupt stoppage, I will stay a little closer to the dock on my next seatrial.


Lesson learned- do not stop thinking about the problem even when the answer seems obvious.

[LittleWing77]

I love problem-solving stories like these.

Well done, Sanibel!
LittleWing77

[Chotu]

Same thing happened with my very low hours (but stored a few years) Tohatsu.

I would seize after a while of using it, even though there was a good stream out of the telltale.

The fix was the thermostat. It wasn’t opening at the right temperature, which allowed it to run just like yours, then seize just like yours.

It’s definitely a cooling system issue. Can only be clogged up cooling gallery in the head of the engine or thermostat.

One small detail I’d missed over the years was I thought the telltale showed water spraying out from the cooling area inside the head. It’s does not!! The telltale only shows you have water coming from the impeller and making it up to the entrance of the power head. It does NOT mean you have cooling water in the head itself. The thermostat and clogged up galleries in the head can still prevent cooling even with the telltale spraying nicely.

Take a peek in the galleries to see if they are clean or not. And run without the thermostat if they are clean to test. If it works, get a new thermostat. You probably don’t need to rebuild anything. They are fairly durable. I overheated mine to the point of seizing about half a dozen times before I knew what was going on. Works just fine without a thermostat now. Waiting to get one once I can get somewhere that I can receive things in the mail.

[Captn_Black]

I fixed a similar problem for someone else, it turned out to be hard caked salt in the outlet. Remember to flush it in a big bucket of fresh water after use, or with a hose attached to the inlet port designed for that purpose. At least occasionally, and certainly before long term storage.

[sanibel sailor]

Originally Posted by Chotu

Same thing happened with my very low hours (but stored a few years) Tohatsu.

I would seize after a while of using it, even though there was a good stream out of the telltale.

The fix was the thermostat. It wasn’t opening at the right temperature, which allowed it to run just like yours, then seize just like yours.

It’s definitely a cooling system issue. Can only be clogged up cooling gallery in the head of the engine or thermostat.

One small detail I’d missed over the years was I thought the telltale showed water spraying out from the cooling area inside the head. It’s does not!! The telltale only shows you have water coming from the impeller and making it up to the entrance of the power head. It does NOT mean you have cooling water in the head itself. The thermostat and clogged up galleries in the head can still prevent cooling even with the telltale spraying nicely.

Take a peek in the galleries to see if they are clean or not. And run without the thermostat if they are clean to test. If it works, get a new thermostat. You probably don’t need to rebuild anything. They are fairly durable. I overheated mine to the point of seizing about half a dozen times before I knew what was going on. Works just fine without a thermostat now. Waiting to get one once I can get somewhere that I can receive things in the mail.

Don't think mine has a thermostat. I will look again. To be honest, I looked harder for a thermostat in the manuals than I did on the motor. There is very little info in either the owner's or service manual about the cooling system. I assume to check the galleries, I pull the head?

[Chotu]

Originally Posted by sanibel sailor

Don't think mine has a thermostat. I will look again. To be honest, I looked harder for a thermostat in the manuals than I did on the motor. There is very little info in either the owner's or service manual about the cooling system. I assume to check the galleries, I pull the head?

You don’t have to pull the head.

Just open up the area of the power head where the telltale hose is attached and have a look from there. The telltale hose is attached to the beginning of the cooling system in the power head.

It will typically be attached to a sort of rectangular pancake which actually makes up a portion of the cooling gallery. It’s like a cap on part of the water flow area. Just looking in from there you’ll be able to see if it’s all full of crud or reasonably clean.

If no thermostat, it really starts to narrow it down to:

1) gunked up cooling galleries and water jacket
2) blockage of some other sort in cooling galleries
3) very remote possibility the flow coming from the impeller is sufficient to make the telltale work, but too slow to cool the engine.
4) blockage at the outlet of the cooling system

It actually can’t be anything else.

[sanibel sailor]

Looked closely-at the motor and catalog. No thermostat, no access plate. I guess the head has to come off.

[sanibel sailor]

Pretty simple. Few parts. May be able to pull head with minimal disassembly.

[Chotu]

https://m.youtube.com/watch?v=XVecUwWDP90

This is it, right? If so, it appears you’re right. It’s extraordinarily simple and appears to supply the telltale straight from the water jacket.

Sorry. It’s a difficult outboard to check all of this with.

[sanibel sailor]

That is an older one with a metal fuel tank. Otherwise same Nissan NS5B.


I ordered a new head gasket. Less than $10. I think if I remove the tank, I can get the head off with no other disassembly needed. I might even splurge for a new plug.

[Sailmonkey]

I’ve taken those apart before and had to chisel the salt buildup out of the jacket. It’s easy after you spend the 5 mins to get the head off.

[sanibel sailor]

My first outboard cylinder head off.
Head gasket finally came. Supposed to be 8-10 days. 3 weeks late from China.
Tank off and nothing else required to pull head. 5 bolts. Came off easy. Head passages had lots of crud, cleaned that out. Kind of weird, only one big hole in/out. Cleaned crankcase surface, careful not to scrape the copper cylinder sleeve, (thinking to myself but ignoring the thought that a copper sleeve is odd) and discovered a little hole into the head which was plugged. Got the hole cleared and put the head back on with the new gasket. Started torqueing the head down, but needed an extension I didn’t have in my toolbox. While I am wandering around getting ready to go fetch it, I wondered if the new gasket had a little hole also. Looked online and saw pics with and without. Parts manual shows a hole. Take head off and sure enough, it has a hole. Then I wonder if the old one had a hole and maybe that’s why it clogged. I look around the work area, in the trash, inside, all around and I cannot find it. I am sure I removed it. Oh well, doesn’t matter. It is not until I am driving to my storage area for the tool that I realize why I can’t find it. Still on the crankcase. Get back home and sure enough, 2 on there...
Remove both and there’s the crappy cylinder water jacket. The corrosion not only blocks water passages but must be a much less effective at heat transfer than bare aluminum. Cleaned out, reassembled with just one head gasket, torqued to... no specs in manual, splurged for a new $2.59 spark plug. Ready to go. Dark by then and I didn’t have a bucket for a test start but I imagine she’ll be a lot happier.

[rbk]

If that doesn’t do it, drop the leg and check the supply tube from the water pump. Carrier tubes don’t alway align/seal well and gaskets fail. Just repaired a Suzuki with brand new pump housing that didn’t have a top water seal, it would pump water enough to idle or troll but didn’t last long at 80% throttle and up. I would wager that when the impeller was replaced 7 years ago the water tube wasn’t aligned to the top of the pump housing and/or poorly sealed. That could also be causing all the crud in the head due to low flow and higher temps.

[sanibel sailor]

Thanks for the tip. This one seemed to seat/seal well when I replaced the impeller and reassembled. This particular model is very simple.

[rbk]

Also check for scoring on the inside of the pump housing. A piece of gravel or sand stuck in there for even a bit can gouge a rut in the housing/cartridge, providing inadequate flow.