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Exhaust manifold is leaking - can you help me identify the leak?

T

tyoung560

New member
Hi all,

First time owner here and I’ve been trying to work through a raw water issue.

My boat is 1990 Glastron Sierra with an aq131c engine. My first outing with the boat resulted in overheating, the engine started overheating within minutes of launching, we turned off the engine at 250 degrees and paddled our way back to the dock.

The raw water impeller was missing all of its fins. I’ve just installed a replacement and started the boat + muffs to see if I have water exiting from the prop - indicating water is flowing.

Impeller is working well now, but I was still not seeing water exiting the prop but my main concern was the water spraying out from the underside of the exhaust manifold.

After turning off the engine, I recorded the attached video. This is taken from underneath the manifold, by leaning over and extending my arm under the manifold.

Any help would be appreciated - I’ve seen some mention of frost plugs, which this looks like it could be one? The circular area is not sitting evenly with the manifold itself, when rubbing my fingers around it, it feels titled.

I’m not 100% sure this is where the water is actually leaking from, as I couldn’t get video of the leak as it was actively happening.

Is replacing the manifold a difficult task or is it basically just bolts and gaskets?

Video can be viewed here - https://drive.google.com/file/d/1CGNHctlMYw1XDoxIfyEUng0HV3VoT1Th/view?usp=drivesdk
 
Just took a few photos of the affected part and location in the video.

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Its pretty much nuts and bolts and gaskets...and hose clamps.

It may be the freeze plug - won't hurt to change it...and the brass ones last a lot longer than the steel plated ones.

worst case is you'll have to get an aftermarket replacement manifold...

On the old impeller fins being "missing" - its very possible some of those parts are blocking the waterflow...they usually get hung on the fittings and elbows - anywhere a restriction exists...not saying it has happened in your case but if overheating occurs, I'd say that's the next step...
 
makomark said:
Its pretty much nuts and bolts and gaskets...and hose clamps.

It may be the freeze plug - won't hurt to change it...and the brass ones last a lot longer than the steel plated ones.

worst case is you'll have to get an aftermarket replacement manifold...

On the old impeller fins being "missing" - its very possible some of those parts are blocking the waterflow...they usually get hung on the fittings and elbows - anywhere a restriction exists...not saying it has happened in your case but if overheating occurs, I'd say that's the next step...
Click to expand...


I've found maybe half of the old impeller fins. I am concerned that there are more stuck throughout the system but this leak is my main concern at the moment.

RE: freeze plugs, the silver circle closest to the actual exhaust pipe is the one I would knock out and replace? I know nothing about these but based on a few mins of looking around, it looks like mine is backwards? Shouldn't the cup be facing outwards?
 
I would agree as that's the way I always have seen them (and say the same for the plugs in the engine block as well).

Measure the opening with a dial caliper...the outer edges of the plug usually have a small taper. I use locktite on the circumference of the plug and prefer to set them with a driver set...if you don't have those, you can use a socket and a hammer...just go slow and keep the plug square to the bore.
 
Thanks for your replies @makomark

My plug definitely looks a bit popped out, here's a reference picture compared to my own. What would cause them to pop?

REFERENCE:

Snag_36cda952.png




MINE:

exhaust.jpg
 
In my decades, they usually 'pop out' when the water behind them freezes....they usually 'leak' when they rot thru (if they haven't popped out)...

Maybe volvo calls for them to be installed with the lip in instead of lip out...
 
I think I'm going to have to pull this manifold off regardless to deal with the plug situation + test for flow. I'm quite worried about that water pipe flange though, she's looking SUPER rough from these photos.
 
Update: I was able to gently hammer the suspect freeze plug inwards enough to seat it a bit more uniformly. The result was a slow drip of water rather than a constant spray and we now have water exiting the exhaust!

IMG_1072.MOV

drive.google.com drive.google.com
 
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