9.8 hp Mercury will not pump water, even though every thin checks out well.

[burnie]

I have searched the site for answers and only find what I have already tried. My 1978 110 mercury 9.8 hp will not keep peeing. I replaced the impeller, and it is set well in the housing with the key pin in place. It is not slipping. With the lower unit off, I flushed all lines, cleanning out lines from water source to the pump and water tube to the taletail. With a water hose, I can run water from the lower water tube easily through engine and out the pee hole. In other words it appears nothing is clogged. The water pump housing appears to seal up easily and well. The gasket (if that is what you call it) in the housing that connects the water tube to the housing appears to be in good shape. Impeller spins as it should while hand spinning the shaft after the housing is back together. Once I put the lower unit on and run the motor in a bucket, it will pee at low speeds, but once the rpms go up, it stops and only air and steam comes out. When rpms are lowered back down, it still won't pee. If I kill the engine and restart, it will pee again. Im stumped. I do admit to not being familure with this motor and know im missing something. Im sure you fine folks can put me on the right track.

Thanks Kent.

 

[Wingedwheel]

Re: 9.8 hp Mercury will not pump water, even though every thin checks out well.

Sometimes with those smaller motors, the leg has to be totally submerged. If you can, put your boat in the water and see if it works for you that way. I had that problem awhile back and it was driving me crazy. I finally put the boat in just to see and everything worked fine.

 

[DamianJP]

Re: 9.8 hp Mercury will not pump water, even though every thin checks out well.

Hey burnie

Makes sure the lower unit is in the water far enough first like Wingedwheel said.

My older nephew is having the same problem on his 200 HP offshore.

***I dont want to worry you, so If someone could concur with my hunch that would be nice, before you think the power head needs to come off***

The problem explained to me by his mech was there's a plate and/or gasket the seperates the water and the exhaust. When the exhaust builds up enough to block the water from coming up thats when you get the "steam". This plate and/or gasket need to be replaced involving the power head coming off. Granted his is a 1996 and bigger motor, but your symptoms are almost identical.

Again I don't want to worry you, but I hate to see you waste more time and money without throwing this out to the forum to see if this is the problem.



Lemme know,
DamianJP

 

[burnie]

Re: 9.8 hp Mercury will not pump water, even though every thin checks out well.

Thanks Wingedwheel and DamianJP

I put the motor deeper in the barrel which did not solve the problem. arrgggg.

something else I forgot to mention. While running water up the lower water tube, I look up in the motor and noticed water was coming from two slits under the power head as well as flowing out the pee tube on top. Not sure if this normal for this engine.

 

[huntin dawg]

Re: 9.8 hp Mercury will not pump water, even though every thin checks out well.

Sounds like you have encountered what seems to be pretty common on these motors. It sounds like the exhaust cover gaskets need to be replaced. Pretty easy fix. Just make sure all mating surfaces are clean and flat so everything mates up even. There are two gaskets sandwiched between the cover, a baffle plate, and the powerhead. Kind of like a Big Mac.

HD

 

[burnie]

Re: 9.8 hp Mercury will not pump water, even though every thin checks out well.

Thanks huntin dawg. Just one question, do I only have to remove the exhaust cover to see this, or do I need to remove the power head as well..

Thanks again.

 

[burnie]

Re: 9.8 hp Mercury will not pump water, even though every thin checks out well.

well i pulled the power head and found one paper gasket. it looks to be in bad shape. Now to the exhaust cover. Im pulling it all apart to so I can get a good Idea of how this motor works. Until now, all ive ever had were johnson's

 

[emckelvy]

Re: 9.8 hp Mercury will not pump water, even though every thin checks out well.

I'd agree that your symptoms sure do point to bad exhaust manifold gaskets. Use caution when removing the cover bolts, if they don't come free with normal force be sure to heat them up with a torch as they're probably seized. Very easy to break these bolts and fixing that is no fun!

Inspect the exhaust baffle plate as well, renew if it's badly pitted or perforated.

While you've got the powerhead removed, take a look at the rubber grommet where the water tube comes up to the top. If the grommet looks squeezed-in, replace it. There should be a plastic washer on top of the water tube grommet. Merc has put out a water tube washer with upgraded material (looks like phenolic to me) that will not warp with heat and close off the water supply. Definitely a good upgrade if yours is the old-style plastic.

Torque the manifold cover bolts to 90 inch-lbs. Use some Permatex #3 aviation-type gasket dressing on the bolts and they'll never get stuck. The plus to this is you'll be able to periodically re-torque the bolts to prevent future leaks.

Here's a few places with parts diagrams so you can look up part numbers etc:

www.boats.net

www.crowleymarine.com

www.mercruiserparts.com

HTH & G'luck with the repairs...........ed

 

[burnie]

Re: 9.8 hp Mercury will not pump water, even though every thin checks out well.

Thanks a million emckelvy

I got the exhaust manifold cover, plate, and gasket. The plat looks A.O.K. The bolts came out pretty easy with a few real easy to get out. Between the plate and the cover, it looks like water was leaking into it. There was lots of water deposits in it. The exhaust side of the plate looked clean.