Mercury Outboard cooling / overheating / impeller

Chrsamss

Seaman
Joined
Jul 7, 2009
Messages
54
Hello,
I have a 1992 Mercury 115hp outboard, the other day I was slowly going around the marina when I noticed it was not pissing out water. I put my finger over it and felt hot air, I also noticed water bubbling up from the mounting bracket area or the exhaust housing. It was bubbling up so hard that it was hitting the underside of the engine cover.

I originally thought the impeller had failed however the bubbling water makes me think that it is still pumping. Has anyone come across the impeller housing or gasket failing is such a way to get this bubbling and to stop the cooling of the engine.

Any thoughts or wisdom would be appreciated.

Thank you
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,544
On my 90 the tell tale is plumbed right off the exhaust manifold. Easy to follow the hose to an ell on the long, flat plate, on the port (left looking forward) side of the engine. Yours should be there too.

With this plumbing, the pee should start as soon as the impeller gets the exhaust manifold water jacket full of water. This has nothing to do with the thermostat or high pressure popoff which control flow to the block interior. Since you said you felt hot air then it must be open and not clogged by a dirt dobber or debris. With your problem I would suspect either a clog in the water delivery line either prior to the impeller or after. The clog could be a broken off impeller blade. Or with what you have said you could have blown the gasket where the block and mid section mate allowing the water to exit rather than going on up to the block. With the limited exposure I have to your engine and what you have said, I would suspect that you are correct that the water pump is performing normally.

Mark
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,544
On my 90 the tell tale is plumbed right off the exhaust manifold. Easy to follow the hose to an ell on the long, flat plate, on the port (left looking forward) side of the engine. Yours should be there too.

With this plumbing, the pee should start as soon as the impeller gets the exhaust manifold water jacket full of water. This has nothing to do with the thermostat or high pressure popoff which control flow to the block interior. Since you said you felt hot air then it must be open and not clogged by a dirt dobber or debris. With your problem I would suspect either a clog in the water delivery line either prior to the impeller or after. The clog could be a broken off impeller blade. Or your seals on the copper interconnect line between the outlet of the water pump and the block may have failed not allowing pressurized water to move on up to the powerhead. With the limited exposure I have to your engine and what you have said, I would suspect that you are correct that the water pump is performing normally. Since the midsection is open it is highly possible that the lower seal is the culprit, the one at the outlet of the water pump housing.

Whatever you do dropping the lower unit is going to be a necessity and while in there might as well have a look at/replace the impeller too.

Mark
 

Chrsamss

Seaman
Joined
Jul 7, 2009
Messages
54
I took the boat to a mechanic and they took the head off and replaced the exhaust plate they seem to think this would work. I went to run it today and the water is coming out of the telltale however when I rev the motor up there is water gushing out the back of the exhaust housing ,where the two rods (or motor mounts??) from the hull bracket enter the midsection.... is this normal? See the picture..thanks
 
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