Nissan NS8B cooling problem

[babylonlarry]

I just bought an old NS8B. Upon running it, there was no water coming out of the powerhead bottom outlet. If I blocked this outlet with my finger, the exhaust bubbles increased in the housing underwater. I took the lower end out to inspect the water pump and the pump, impeller and tube rubber seem good. I blew into the water tube and it passed air and water but not to the head outlet. I poured white vinegar into the tube and outlet hoping to unblock salt build up and am hoping that I can unblock it without taking the powerhead apart.

What kind of connection is there from the tube that runs up from the pump to the powerhead? It seems a bit loose.

I have a service manual that covers 2.5 thru 40c but not the NS8B. It has a M8B and a NS9.9B2

I followed the 9.9 disassembly and pulled the wrong pin in the shift rod (no biggie) but would like to know how to proceed if I need to do more dissassembly.

TIA for any help on this, Larry

 

[pvanv]

Re: Nissan NS8B cooling problem

First things first... Get the Factory documentation. The parts catalog is available on Tohatsu Guru's excellent website at http://www.internetoutboards.com/PartsCatalogMenu.htm I'm not in the office today, so I can't confirm availability, but odds are that any Tohatsu/Nissan dealer should be able to get the Factory service manual for you. You can do a search for your nearest dealer from Nissan's website at http://www.nissanmarine.com/ The aftermarket manuals are Ok for very general information only, but otherwise make decent doorstops or woodstove tinder. The 2-stroke 8/9.8 is a completely different family of motor from the 9.9, so don't rely on that aftermarket manual to help you too much.

The tube from the water pump to the powerhead is L-shaped at the top, and it's not uncommon for it to be a bit loose in the top grommet without any problem. The water pressure normally tightens it up. Also, it's common for the cooling telltale "p-hole" to be stopped up with debris or salt. You can safely push a stiff wire into it (or a short blast of compressed air) while running, to see if that clears a clog. Usually does, and the junk will normally get flushed out. The telltale shows that the water system is pressurized, but that is all -- it does not show whether water is circulating through the cooling system.

If you see an increase in exhaust bubbles when you block the p-hole, then you may have a bad base gasket, allowing exhaust to pressurize the cooling system, with exhaust trying to exit via the telltale. Not difficult to change. But get the telltale working, and confirm that the motor isn't overheating, before jumping to conclusions. Your motor is equipped with a thermostat, so it should warm up fairly quickly, and then the stat should regulate the temperature fairly well. The fact that you can blow air and water through the cooling system is a good sign, proving that the cooling system is not completely stopped up with salt and junk.

 

[TOHATSU GURU]

Re: Nissan NS8B cooling problem

NS8B = M8B...Different decal.

 

[babylonlarry]

Re: Nissan NS8B cooling problem

Thanks for the info. The parts catalog is very helpful both for ordering parts and for seeing how components are assembled.

I cleaned out the cooling tube with vinegar, spun the water pump (drive shaft) with a drill to see that it put out water, reassembled the lower unit, had small amounts of water come out the pee hole and within a couple of minutes of 1/3 throttle in gear, there was steam coming out of the pee hole and the engine too hot to keep a hand on. Took it apart and repeated the tube cleaning, this time with muriatic acid. Lots of bubbling and particulate matter came out and after a couple of rounds of acid and flush, I could easily blow water out of the pee tube from the water pump lift tube with the engine upside down.

Reassembled, ran and this time no water out of the pee tube but the engine is running at normal temp - that is after a couple of minutes wide open, I can easily keep my hand on the engine. I should determine if the base gasket is NG and if so, replace it. I'm gonna take it for a longer spin soon and keep an eye on the temp. Later, Larry

PS went on a 45 minute ride, half the time planing in a 10' RIB and the engine ran cool, but with only a bit of spray coming out of the pee hole.

Don't know if I should be worried about the lack of pressure in the cooling system or not.

 

[TOHATSU GURU]

Re: Nissan NS8B cooling problem

Keep in mind that most of the water being expelled from the engine is coming out though the prop and only a small amount of water comes out the motor leg...The tiny stream that comes out the pee tube is just an indicator. If it has a strong stream you know your cooling. If it is a weak stream or no stream it just means that you need to verify that you are still cooling. You have done that so you should be fine.

 

[robert2]

Re: Nissan NS8B cooling problem

i have a 92 nissan 5hp 2 stroke.i did my third water pump kit in 4 years today,every year goes well.this year when i was done an ran it the pee hole had a gread stream at idle for 20 min then no water stream just steam and motor began to over heat,took it all apart and everything with the pump kit looks fine

 

[pvanv]

Re: Nissan NS8B cooling problem

First off, you should be making a new thread, as you are posting to a very old thread about a different motor.

If you're getting steam, you don't have water flowing. Either a chunk of debris is clogging the water pipe up from the pump, the tube isn't seated in the upper pump housing, the impeller isn't keyed onto the shaft, or something similar.