Water leak behind in bellhousing Mercruiser 120

[Thagan]

Hello,

I bought an '84 Bluewater with a 2.5 Mercruiser and Alpha 1 outdrive last year. Used it all last summer and winterized. Must not have done the best job because it is leaking water behind the bellhousing and down into the flywheel. I understand I may be an idiot for not properly winterizing and I accept that.

Today I decided to tackle this issue. I removed the stern drive and pulled the engine. Removed the flywheel and I can't see anything wrong. Both "freeze" (not what they actually are meant for) plugs are still there and I don't see any cracks in the block.

The water was leaking in when I was the running the engine on muffs and when I went to the lake a couple weeks ago. I'm not sure where to go from here.

Thanks

 

[Scott06]

Run it off a hose while you have it out and see where it leaks

 

[Thagan]

Run it off a hose while you have it out and see where it leaks

Think it's possible to pressurized the system with water instead of running It? Either way would probably work. Although I'd have to put the flywheel back on

 

[Scott06]

Yes but probably easier to pressurize with compressed air. Plug the water in and out hoses with pipe fittings, rig up a from/to to get air in and have a gauge 10-15 psi is all it takes, if it drops start looking for leaks, can spray the plugs with soapy water to find leaks

 

[Bt Doctur]

considering there is no water connection on that side of the motor and the core plug is intact and there are no signs of a crack look at the manifold side .
Block cracks usually happen behind the manifold and it does look rusty on that side of the engine

 

[Thagan]

Yes but probably easier to pressurize with compressed air. Plug the water in and out hoses with pipe fittings, rig up a from/to to get air in and have a gauge 10-15 psi is all it takes, if it drops start looking for leaks, can spray the plugs with soapy water to find leaks

Stupid question but doesn't the expelled water from the engine go through the exhaust? My plan was to make a block off plate on the manifold (almost where it goes into the rubber boot) and then pressurized the system.

considering there is no water connection on that side of the motor and the core plug is intact and there are no signs of a crack look at the manifold side .
Block cracks usually happen behind the manifold and it does look rusty on that side of the engine

The whole back of the block had rust all over it. I hit it with a wire wheel on a drill for a better inspection. But I will look there too. The front core plug is partially pushed out and has rust trails coming from it but it was not leaking in the water or on muffs.

It was for sure leaking behind the bell housing as I fiddled around with it trying to find the source for a good 10 minutes and came to the conclusion it was a core plug. But I've been wrong many times.

Also, there are 2 drain plugs where someone has stripped the threads on the manifold and I decided to fix them. A previous owner fixed it with some kind of sealant on a smaller bolt shoved in the hole. Surprisingly didn't leak.

 

[Fishermark]

Was there water in the bellows? There is an overflow hole there for water that might get into the bellows. The connection for the water hose is also back there. These are just some additional things to check out. I agree that there is nothing on the back of your engine that has been leaking water. That core plug looks just fine.

 

[Thagan]

Was there water in the bellows? There is an overflow hole there for water that might get into the bellows. The connection for the water hose is also back there. These are just some additional things to check out. I agree that there is nothing on the back of your engine that has been leaking water. That core plug looks just fine.

There wasn't any water in the main bellow. The one where the drive shaft runs through just had some oil (lower unit oil?) sitting in it. I looked at the fresh water line coming from the lower unit to the front of the intake and didn't see any damage to it. When I get home I'll further inspect it.

 

[Thagan]

Hooked up my engine to a water hose and turned it on. It was blocked off before the manifold and no leaks after 3 minutes. Water started leaking around hose connections (probably ~40psi water pressure) so I'm sure my block is fine.

I guess next step I'll build a block off plate and check the exhaust manifold and report back.

 

[Bt Doctur]

no need to build anything just fill the manifold with water .extend the hose to match the manifold height .
and invest in some shackles

 

[Thagan]

The manifold doesn't need to be pressure tested?

 

[Bt Doctur]

If it has a crack and its leaking on the outside you`ll see it. if it was leaking inside you would hydrolock it

 

[Thagan]

If it has a crack and its leaking on the outside you`ll see it. if it was leaking inside you would hydrolock it

Ok makes sense. I will report back my findings tonight. Didn't see any cracks on the manifold when I was inspecting it but I'm usually wrong.

 

[Bt Doctur]

You said water was leaking from the starter area , with no engine issues or manifold issues all thats left is a very high bilge level with the flywheel picking up the water and slinging it around .

 

[Bt Doctur]

The water was leaking in when I was the running the engine on muffs and when I went to the lake a couple weeks ago. I'm not sure where to go from here.

Check the exaust pipe for a corroded hole

 

[Thagan]

I wish I would have diagnosed a lot more before pulling it apart. But what I remember is there was water running down in the center of the engine coming from what looked like the bellhousing. It wasn't leaking from the fresh sea water hose that comes from the gimbal housing to the thermostat housing (I believe).

I guess from this point on I need to assume anything is possible. Boat was drained before I ran on muffs so no water splashing. It had a lot of water in it when I was out on the lake for a couple hours. Didn't see the leak but assumed that was why it had so much water in it.

 

[Thagan]

Filled the exhaust manifold with water and no leaks. Seems to be holding just fine after 10 minutes. Exhaust manifold looks fine visually. Don't see any cracks or other issues.

I feel like an idiot. I thought for sure it would have been a core plug on the back of the block. That's why I didn't bother to look around more. I guess I'll just order a couple new gaskets and throw it back in.

 

[Grub54891]

Filled the exhaust manifold with water and no leaks. Seems to be holding just fine after 10 minutes. Exhaust manifold looks fine visually. Don't see any cracks or other issues.

I feel like an idiot. I thought for sure it would have been a core plug on the back of the block. That's why I didn't bother to look around more. I guess I'll just order a couple new gaskets and throw it back in.

Don't feel bad, More people make worse decisions, in your case, now you know that the aft end of the motor is solid, and further diagnosis will be easier just knowing that.

 

[Bt Doctur]

Before you put the motor back in inspect the Y pipe a typical housing

 

[Thagan]

Don't feel bad, More people make worse decisions, in your case, now you know that the aft end of the motor is solid, and further diagnosis will be easier just knowing that.

Yeah that is a good point. This is also a great time to fix a couple small issues and to inspect/replace some parts that required this much disassembly.

Before you put the motor back in inspect the Y pipe a typical housing

Where exactly is that location?