1999 Yamaha 90 - 2 stroke 3cyl
 

While recently running the outboard on the hose hook up, I noticed that the water pump stream coming out the side of the motor was flowing, but not very strong. After idling for 10 minutes giving it gas every so often, I also noticed that the two back exhaust/water ports never released water. The stream of water began to warm up and the lower unit started to get mildly hot. At this point I killed the motor. I purchased a new impeller kit from yamaha, and still have not installed. I am wondering if the problem could be a broken thermostat, preventing the outflow from the two back ports. The local yamaha dealer said that the impeller probably needed changing, but never mentioned the possibility of a broken thermostat, which would circulate water through the engine block. Could this be a possibility? Thanks in advance.

Pay attention to the wear plate and impeller housing when you change the impeller. If there is any grooves change them. As far as the thermostat goes,get rid of it. They are useless on a carb 2 stroke in louisiana heat. Take the thermostat out and cut the guts out with cutting pliers and just re install the cap.

My main question is, how long will it run before water begins to come out of the two back parts, and if it doesn't is this an idication that the water isn't circulation through the engine?

back ports*

Back it down at a boat launch,running it on the hose it not a good test. Should not take long....a min or so if that long. Gut the thermostat and you won't have to worry about it.

impeller. this happen to our 75hp yamaha also...and now it running greatt

the water coming out of the "pisser" should be getting pretty warm... as it is cooling the engine, the engine is heating the water.

I realize that, just wondering if it is fully circulating through the engine, as the two pack ports aren't releasing water...

I will change impeller and see what happens after.

I meant two back ports

Are speaking of the two rectangular exhaust ports right below where the cowling latch is below the lower cowling....if so, mine never has water come out of them, just out the pisser.

my lil 50 yamaha barely even has water coming out the two ports on the back. its like a drip mist. i change my waterpump every year and its done that since i owned it. if its been a while just change the pump. like montaulk said gut the thermostat it helps out a lot in the summer and you dont have to worry about it clogging up if you hit some mud or grass. i wouldnt judge the water flow while running on the hose. put it in the water.

the water that you are thinking of will be coming out the center of the prop exhaust...hook it back up and check it out, should dump plenty of water with exhaust when throttled on and off..

Yup gotta have the back pressure of the lower unit being under water.

yeah, same here... i have a 50 yammy and it comes out the prop and the "pisser" that's it... when hooked up to a hose

Thanks really appreciate all the input

You can check the thermostate. Take it off the engine and put enough water in a pot to cover the thermostat and turn the stove burner on hi. The thermostate should start to open [~190 F] when you start to see bubbles forming on the bottom of the pan.

Make sure you check the swash plate. If any wear I would replace. I recomend leaving the thermostat in the motor to maintain proper engine temp..

I was told by Jerry at Jerry's Marine to NEVER run an engine without the thermostat for an extended period of time. I think it has something to do with the cylinders being too cold compared to the piston and causing excess wear.