Mercruiser ~ water coming out of spark plug

I've got a 1984 Avanti with a 1.7L Mercruiser (4 cyl). I noticed that it was running a bit rough while cruising at lowest speed. Upon inspection of spark plugs I noticed that a small amount of water is seeping through the plug closest to the back of the engine (sorry, not sure what # plug that is). I noticed water was seeping through slowly both while the boat was running as well as after I had stopped the engine. I would mop up the water with a rag & it would come back through the plug again slowly (without engine power). It's definately water, although I did detect some gas odor as well. I also checked the oil and don't see that the oil is "milky". I didn't run the motor long after noticing the plug leaking (just long enough to get it pulled out of the water at nearby boat ramp). What could cause water in the plug, and is this a really, really bad thing?

A day before I noticed the water seeping out of the plug (I had the boat docked at the lake), the boat started taking on more water than usual and had gotten up almost to the engine overnight. I pumped it out as soon as possible, of course, but was wondering if somehow the engine could have taken in some water and that could be why it's seeping through the plug?

I found out that the water is coming from the screws in the transom holding on the prop...could this be the boot leaking (that I had replaced just 2 years ago?!). Shouldn't boots (or bellows?) last longer than a couple of years?

Thanks for taking the time to read over my problem!! I hope that I provided enough detail (or not too much either). ~ Cowgrl

Re: Mercruiser ~ water coming out of spark plug

Welcome to iboats. First, I severely doubt that the water you see is seeping out of the plug. It should be in tight enough to contain the explosion that happens in the cylinder every time it fires, so that usually does not allow any water that may be in there to seep out. Most likely it is dripping from something above (head gasket or exhaust assembly) or it is splashing on from somewhere else. Second, did you inspect the bellows for obvious cuts or holes? They do develop leaks for any number of reasons, regardless of age.

Re: Mercruiser ~ water coming out of spark plug

stevieray said:

Welcome to iboats. First, I severely doubt that the water you see is seeping out of the plug. It should be in tight enough to contain the explosion that happens in the cylinder every time it fires, so that usually does not allow any water that may be in there to seep out. Most likely it is dripping from something above (head gasket or exhaust assembly) or it is splashing on from somewhere else. Second, did you inspect the bellows for obvious cuts or holes? They do develop leaks for any number of reasons, regardless of age.

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Re: Mercruiser ~ water coming out of spark plug

Thanks for your reply! Myself and my boyfriend looked closely at that plug in question and both agreed that it's definately seeping through the bottom of the plug ~ I would wipe up the water seeping through and it would start filling up again from the bottom of the plug/housing (although we've not taken the plug out at this point or done anything else to it yet..wanted to research first).

Did check out the bellows and didn't notice anything out of the ordinary like obvious cracks etc. (just a spot check when we pulled it out of the water though, maybe a closer look will reveal the problem...although it seems to be coming in at 3 different plugs on the inside of boat when submerged). Do you have any idea what the "life expentancy" is on new bellows/boots? 2 years - 5 years?

Thanks!!

Re: Mercruiser ~ water coming out of spark plug

The seapage around the spark plug is a cracked head, that's all it can be.

The bellows are usually good for 5 years, but they are not the only things that can leak water. The big ring on the inside of the pivot housing can leak, especially if someone tried to reuse it.
Then there is the shift cable bellows, the plug for the trim wires, the water tube, the exhaust tube connection.
You're just going to have to get in there with a mirror, flashligths, or what ever to find out what is leaking. May be the transom itself.

Regarding your engine, it is the 3.7L (470 style) engine? There is a 1.7 Engine, but it's a diesel.