Small water leak from Merc 5.7L

[Bren118]

Hi everyone,

long tome reader, first time poster.

I just bought my second boat, a 1998 Mariah Talari 216 cuddy. It’s powered by a carbbed 5.7 mercruiser and an alpha one gen 2. I’m moderately knowledgeable when it comes to motors and did a lot of my own work on my first boat.

The mariah runs great. I engine noises, starts right up. No issues whatsoever running.

However, I noticed small drips of water coming from the stbd side of the motor when I had it on the muffs yesterday. Something I hadn’t noticed while checking is out at the seller’s house.

While trying to diagnose the leak. I made sure to check the oil, which is perfect. No milkshake, or signs of intrusion. I ran the motor on the muffs at 1000 and 2000 rpms and the drip remained the same frequency, 1 drip about every 3-4 seconds. It’s a tight squeeze into the engine compartment but I can feel one of the block drain plugs is very wet and the seam where the oil pan meets the bottom of the block is wet. It also looks like there may be a light streak of water coming down the side of the block. Makes me think the light steak of water is traveling to that seam and over to the plug where it’s dripping from.

I cant however, for the life of me find the definite source. My questions are. Could the block be cracked? Literally no other symptoms of a cracked block (I’ve dealt with that before). Or is there a common area that springs leaks around there? I also see next to the streak of water on the block other rust streaks were it looks like water has run in the past so I believe it has been like this for a while. Since it’s so slow and not a serious, flowing leak, should I just keep an eye on it and see if it gets worse? My wife thinks I’m freaking out for nothing and I hope I am.

thanks in advance for advice.

 

[Bondo]

It’s a tight squeeze into the engine compartment but

Ayuh,...... Welcome Aboard,...... Any leak on a boat should be investigated, 'n fixed,.....

A digital camera in yer hand will put yer eyes, where yer head don't fit,......

Water flows downhill, so keep lookin' higher, til it's dry,.....
Whatever is just below that point is where the leak is,.....

It's more likely an exhaust manifold leak than a cracked block, but yer camera should confirm whatever it is,.....
The rust tracks are a good trail to follow to find the leak,.....

 

[Bren118]

I should also add, right next to the block drain plug there is some sort of sensor plugged into the block, right above the seam, which is also wet. I have no idea what this sensor or part is, but it could also be the source if it’s a temp sensor or something.

 

[Bondo]

I have no idea what this sensor or part is,

Ayuh,...... It's the knock-sensor for the ignition,.....

 

[Bren118]

Ayuh,...... It's the knock-sensor for the ignition,.....

That makes sense since it’s right next to the starter. That part has no contact with any internal water channels then, correct?

 

[Bondo]

Ayuh,..... The hole in the screwed in end of it is a few thousandths of an inch diameter,.....

Look Higher,.....

 

[Bren118]

Ayuh,..... The hole in the screwed in end of it is a few thousandths of an inch diameter,.....

Look Higher,.....

Thanks. I’ve been reading these forums for years and always look for your replies.

 

[Bren118]

It's more likely an exhaust manifold leak than a cracked block,

If it were the manifold, Would it be right to assume that the leak would be faster while in the lake and under way? Maybe at higher RPMs? Or would the pressure in the manifolds not change enough the make the leaks faster in those conditions?

 

[Bondo]

Would it be right to assume

Ayuh,..... As Don S used to say,...... Assume, Nothing,.....

 

[Bren118]

Well Bondo, I put my camera where my head don’t fit. Didn’t like what I found. Found a few tiny cracks near the top of the block. Maybe a half inch in size each. Also looks like one of the previous owners JB welded the hell out of it but did a pretty bad job because they couldn’t see what they were doing. Also from all the rust around it, it looks like it’s been running like that for a long time. Fortunately, it’s probably not cracked internally because there is zero water in my crank case or in the oil and she runs flawlessly. So I’m a little torn on what to do. Either I replace the block now or wait to see if it gets worse and replace it later. Or I can clean it up a little and JB weld the spots some more.

 

[achris]

.... Since it’s so slow and not a serious, flowing leak, should I just keep an eye on it and see if it gets worse? ....

Find it, fix it... A few months ago I pulled the drive from my boat and found a very small amount of drive oil in the bellows. It was so small that it could easily have been left and 'kept an eye on'... But I didn't do that (not my thing), I opened up the drive, and found a whole pile of worms. Going ahead and fixing that small issue just saved me the cost of a new drive...

Small problems usually end up being big problems, and costing many times more to fix than they would have been if fixed when they were 'small problems'....

There's also the issue of operating a boat, in the oceans or large seas and lake with a known problem. That, in my mind, is dangerous, stupid and irresponsible... A car breaks down, you get out and walk. A boat breaks down, people die!

Chris.......

 

[Bren118]

[No message]

 

[QBhoy]

What you describe is the typical location for the block to crack on a GM V engine.
May be the exhaust manifold but hope for the best.

 

[Bondo]

So I’m a little torn on what to do. Either I replace the block now or wait to see if it gets worse and replace it later. Or I can clean it up a little and JB weld the spots some more.

Ayuh,...... If it were me, I'd slather some more epoxy onto it, 'n run it til it blows,......

Then drop in a new long block motor,.....

 

[Bren118]

Ayuh,...... If it were me, I'd slather some more epoxy onto it, 'n run it til it blows,......

Then drop in a new long block motor,.....

That’s pretty much what I’m leaning toward. Given that it’s external and only weeping, do you think we’d get a few seasons out of it? Like I said earlier, given the rust buildup, it appears to have been running in this condition for quite some time. I appreciate your advice and opinions.

 

[Bt Doctur]

Another reason to get a professional survey
Now knowing that it was from a no/improper winterizing at some point what else could have stress cracks in it

 

[Bren118]

Another reason to get a professional survey

Hindsight is always 20/20

 

[Bondo]

That’s pretty much what I’m leaning toward. Given that it’s external and only weeping, do you think we’d get a few seasons out of it? Like I said earlier, given the rust buildup, it appears to have been running in this condition for quite some time. I appreciate your advice and opinions.

Ayuh,..... Odds are, it won't get worse, unless something stupid is done to it, like not winterizin' it again,....

 

[Pzilly]

You mentioned you had it on the muffs, and the the sellers house, so how long have you owned this boat, if I found Undisclosed JB weld on a recent purchase I would be back at the sellers door step. Now a used boat is a used boat, but Jb weld fo pass on a problem wo disclosure is whole other thing.......