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Discussion Starter #1
I have had my 1988 30hp Mariner/Japanese Yamaha for years. Never had any issues until a few years back I changed the waterpump. Since then every year I have to change the impellor because it quits peeing. Did it again this week after I launched at Alaqua. Changed the impeller today and it pumps.

The stream has always been weak. Sometimes just drips while idling. At higher speeds it puts out more of a stream, but never a strong one. Don't think this motor has a thermostat. If it does I can't find one online. Is there anything that can be done to make it shoot water out the pee hole? Always looking back while moving to make sure it doesn't overheat.
 

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Could be blockage in the water jackets in the head or the thermostat and housing has blockage from broken impeller pieces. Do you replace only the impeller or the complete housing? If always only the impeller, you might ought to replace the housing, plates and all next time.
With the cowling removed, and looking at the sparkplugs, the thermostat housing should be on upper right side of your motor.
 

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Discussion Starter #3
Usually Outboards Unlimited works on the motor. I leave it up to them to do what is needed. This time I replaced the impellor since it was only months since I had them fix the problem. I can't remember ever being told it was the thermostat. I can't find one listed online. The motor is old, but other than the pee issue it has never cost me any money.

When I had the foot off I shot water up the line going up into the head and it peed fine. Maybe I need to have it rebuilt.
 

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Maybe the head needs the water jackets cleared, but I doubt the motor needs rebuilding. I know the guys at OU, and he's really good.
Okay, try this. Get a piece of wire, maybe use a wire coat hanger. Run the wire into the pee tube while you have the
rabbit ears on, and water on. There's a small dirt dobber wasp that sometimes builds nests inside the pee tube, thus causing a blockage.
If it doesn't start peeing better after this, remove the hose from lower (engine off), run the pee tube inside the hose and backflush the system, then try it again with rabbit ears on, water on and motor on.
I do this (backflush) every time I change out my impellers, just in case. And it's really important if the impeller is missing pieces from the blades.
If none of this works for you, take it back to OU and let them know the problem.
 

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Discussion Starter #5
Wonder what OU would charge to clean the water jackets? I also read where a water pressure guage might help.
 

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I'm with curdog...try cleaning the pee tube out with a wire or heavy monofiliment line....something is definitely clogging your system....good luck...
 

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Wonder what OU would charge to clean the water jackets? I also read where a water pressure guage might help.
IDK, but I'd try the wire 1st. If no avail, pull the lower, backflush from pee tube back. Don't let water spray around the sides of the pee tube, you want the full pressure.
You really need to locate the thermostat housing and remove it, and backflush some more.
Double check the impeller, it could have slipped, or have broken blades (you don't know how many years impeller sat on a shelf b4 you bought it).
Also when you re-install impeller, turn driveshaft clockwise as you're pushing the housing over the impeller.
Next, when you replace the waterpump housing bolts, snug them down evenly, before tightening them and, this is very important, ensure the seal or housing is Not touching the driveshaft. If it does, it'll melt the housing and you'll lose water pressure (this may be the actual problem). So back the bolts off a bit and re-snug them until the housing doesn't touch.
As far as adding a water pressure gauge, it isn't really going to help, you already know it's not pissing properly. g/l

Ought to look like this (thermostat & poppet) housing

Mercury 30HP: Outboard Engines & Components | eBay
 

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And if all else fails, pm me your address/cell and I'll swing by and look it over for you.
 

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Discussion Starter #10
Is this the compartment that holds the thermostat? Opened it up and no thermostat. Flushed the motor again and plenty of water came out of this opening. Put the cap back on and it leaks. Now I have to find a gasket.
 

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That's where it goes. If you didn't tear the gasket, you can reuse it. Put a thin coat of gasket sealer on both sides. That little hole is where the poppet goes. If it's missing, that may be your problem. Call NAPA and see if they have the thermostat and poppet kit, or order online (comes with gasket). The poppet controls the water pressure in the head for cooling as does the thermostat. I'd suggest you install both the thermostat and poppet to prevent premature engine damage operating w/o them.
 

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Discussion Starter #12
There is no telling how many years I have been running this motor without the thermostat. Hours and hours on the river. Called OU because I can't remember anyone else who has ever worked on it. They said that they don't remember removing the thermostat. Maybe it just disintegrated.
 

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Discussion Starter #13
I want to thank CurDog for his expertise last week. Even though we replaced the watrrpump and the thermostat with new parts the motor still won't pee like it should.

I talked to OU about clean the water jackets, but since the motor is so old they didn't recommend it. Now I have been told to flush the motor with StarBrite Descaling Engine Flush. I called the company and was told it would clean the water jackets so I figured it wouldn't hurt to try it. Anyone ever used this product?
 

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I've never used it, but by chance did they say to use it with the thermostat in, or out? Just curious, thinking if a big piece of corrosion comes loose, it might could further restrict the water flow at the thermostat. Call again and ask if you hadn't already.
 

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Discussion Starter #15
I am going to ask them a few more questions including that one. They recommended that I buy their winterized kit and use it to flush the motor. I told them I planned to mix the proper amount of concentrate with water in a barrel and lower the foot of the motor into it. No need to spend $50 on a kit.
 
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