Nissan NS50D Over Heat

[mskin314]

Hello all and let me take the time before hand to thank you for reading my post.

I was out fishing the other day, and after running about 15 miles and the motor running perfect I opened her up to WOT and trimmed up. After about 1 minute of WOT I heard the overheat alarm go off. I immediately backed off the throttle and let the motor Idle. I notice Water was coming out of the tell tale. After a few minutes I put the boat back in gear and take off, keeping my RPMS below 4000. I look back and notice that water is coming from the tell tale in bursts rather then a steady stream, and the alarm goes off again. Instantly I go back to idle, water is still pumping out of the tell tale, not in bursts, but not as powerful as usual. The Overheat alarm was on for less the 30 seconds total and I idled back home for another 5 miles and as long as I didn't go above 2000 RPM, everything was fine. When I hooked it up to the muffs/hose, the motor pee'd fine at all RPMS, but I suspect that is because the system was pressurized.

I pulled the lower unit yesterday and took a look at the impeller/water pump housing. It looks bumped and bruised, but still in a functional shape. I took some pictures but cant figure out how to attach them. Could some one help me with that?

Do you guys think I damaged my motor at all? Its a 2000 NS50D with 140 hours. Overheat alarm was on for less then 30 seconds total.

Also, do you think a new water pump/impeller could fix the problem?

Thanks

 

[pvanv]

Re: Nissan NS50D Over Heat

If there is any detectable grooving in either the water pump cup or the wear plate, installing a wp kit would be a good idea. In the cold fresh waters of the Great Lakes, we replace the kit every 3 years unless they need it sooner.

 

[mskin314]

Re: Nissan NS50D Over Heat

This boat is in key largo, so salt water it is. The previous owner put 115 hours on the motor in 11 years. I have put 30 hours in less then a few months. The PO stated that the last time the water pump was serviced was a few years ago...the housing in the waterpump looked good, but the impeller was all nicked up and warped a bit

 

[Sea Rider]

Re: Nissan NS50D Over Heat

If the impeller rotates dry for a short time while at high speed, will ruin the impeller, could have obstructed leg water intakes for a short period while on your way or impeller material went kaput because engine was not flushed after use. If you will not change impeller case liner, get a very used 3M scotchbrite green pad, wet with water, apply a generous amount of any toothpaste and proceed to polish liner and bottom plate with finger pressure in circular motion for a while, rinse, install new impeller, will see a wonderful pee and impeller vanes will last longer.

Happy Boating

 

[TOHATSU GURU]

Re: Nissan NS50D Over Heat

Replace the W P kit. Check the engine compression.

 

[mskin314]

Re: Nissan NS50D Over Heat

One more Question...

Do you guys have any tips when it comes to removing the steel water cup? I see it has a notch in the bottom, but even with some force I can't seem to budge it? Any special techniques ?

Thanks again

 

[pvanv]

Re: Nissan NS50D Over Heat

You can warm the housing with a heat lamp, and it will expand a little... or just good ol' fashioned patience. In severe cases, the upper wp housing will need to be replaced.

 

[Sea Rider]

Re: Nissan NS50D Over Heat

Do you guys have any tips when it comes to removing the steel water cup? I see it has a notch in the bottom, but even with some force I can't seem to budge it? Any special techniques ?

Most of the time is very tricky to remove seized cups inside wp housing, worst if you are not familiar doing so. Don't tell me that 140 hours is a huge use to change cup, they are stainles steel made and very durable in normal water conditions. It's entirely up to you if wanting to polish or replace for a new cup. Will assure you won't see any real pee pressure difference whatsoever with old polished/new cup.

Happy Boating

 

[mskin314]

Re: Nissan NS50D Over Heat

It looks in good condition and I think I am just going to polish it rather then risk damaging it. I will keep the new one as a spare I suppose... Thanks for your help!

 

[Sea Rider]

Re: Nissan NS50D Over Heat

This is a good example of the high quality Tohatsu WP has, outlasts Evis and Yams. This impeller and cup has 2 k meterd worked hours, was placed inside a Tohatsu 30 HP, the engine was used idle to wot for 5 hours daily and engine flushed for 5 minutes after every day use. The cup is still in excellent condition to be polished and just change impeller, was taken out to see its removing easiness, was found completely seized to impeller housing, hard work & patience to remove without damaging impeller housing.

The purpose of using a used 3M Scotbright green pad and toothpaste polishing in circular motion is to remove tiny metal cup scrapes produced by impeller itself, sand, impeller will run much smoother and last longer. The circular wear you might see at upper cup and lower plate will not make impeller to perform poorly, polish both too. Give it a try and let know it it worked for you as it works for us.

Happy Boating

 

[mskin314]

Re: Nissan NS50D Over Heat

 

[mskin314]

Re: Nissan NS50D Over Heat

Please see above for pictures of what I got when I took apart the water pump. Does the impeller look like its in bad enough shape to cause over heating at high RPM?

 

[pvanv]

Re: Nissan NS50D Over Heat

Yes. The impeller has lost its springiness, and will "float" in the pump at higher speeds.

 

[Sea Rider]

Re: Nissan NS50D Over Heat

Definitely your impeller is in a bad shape, completely rounded & hardened, your lower plate & cup has issues on pic marked (X) if it's only metal color change, you could polish both, if completely deep scratched polishing won't remove, will need to change complete kit for engine peace of mind.. The photo examples given are from engines used all year long. When you sat an engine for long periods of time the impeller im most cases becomes round and hardened losing it's flexibility. That's why is good each 15 days if possible to crank engine without starting so impeller changes splines rotation position inside eliptical cup, that is if you want impeller to far exceed it's factory recommended hours change..

Happy Boating

 

[mskin314]

Re: Nissan NS50D Over Heat

Wow guys, I guess its a good thing my impeller is bad, helping explain the overheating at high RPMS.I thank you for your time and help, I will hopefully change the impeller this weekend and do a test run, and will report back with the results.

Once again, I thank you experts for your opinions.

- Matt

 

[Sea Rider]

Re: Nissan NS50D Over Heat

Won't do no harm to check thermostat condition and re torque head gasket to specs, that engine is a 11 years oldie...

Happy Boating

 

[mskin314]

Re: Nissan NS50D Over Heat

Hello All,

Update: I changed out the water pump kit, and changed the lower unit oil and ran the engine for about an hour. There is a noticeable increase in water flowing from the tell tale at all RPMS, and no more overheating issues. The little nissan NS50D pushed my 16 classic whaler to 32MPH, a new record.

Thank you all for your help.

 

[Sea Rider]

Re: Nissan NS50D Over Heat

There you have it, now you have learned how to polish or change impeller cup

Happy Boating