Manifold Replacement

[Thomv]

Oh, the joys of buying used! Having a closer look at on on my 454 Mercruiser engines I notice there are rust stains on the bottom of my hull directly beneath my exhaust manifold bolted to the engine. Looks like it may be leaking. Is it a difficult job replacing? Is there a good write up on step by step instructions? This weekend I plan to take it off to get a closer look at what might be leaking. Before I do this is there a way to pinpoint the leak and should the engine be running?

 

[tpenfield]

Re: Manifold Replacement

The exhaust manifold assembly is going to be 2 or 3 pieces, depending on your particular setup

Manifold
Riser (you may not have this piece)
Elbow

You can visually inspect the joints between these pieces for signs of rust/water.

If/when you take it apart, you will need NEW gaskets to put it all back together, so get those first.

Dis-assembly and internal inspection is a good idea on 5 year intervals. You can get a maintenance manual for specific instructions, Other than being heavy and having some other stuff bolted to them, it is not a hard job.

BTW - You mention Mercruiser, but have posted in the VP forum. So, the Mods will probably move this over for you.

 

[Bondo]

Re: Manifold Replacement

Oh, the joys of buying used! Having a closer look at on on my 454 Mercruiser engines I notice there are rust stains on the bottom of my hull directly beneath my exhaust manifold bolted to the engine. Looks like it may be leaking. Is it a difficult job replacing? Is there a good write up on step by step instructions? This weekend I plan to take it off to get a closer look at what might be leaking. Before I do this is there a way to pinpoint the leak and should the engine be running?

Ayuh,... There's No water that passes 'tween the motor's block, 'n the manifolds,...

Sooo, the water's comin' from elsewhere...

The manifold to riser joint is the most common failure site...

 

[Thomv]

Re: Manifold Replacement

Ayuh,... There's No water that passes 'tween the motor's block, 'n the manifolds,...

Sooo, the water's comin' from elsewhere...

The manifold to riser joint is the most common failure site...

I am going to check over the weekend. Thanks for letting me know what to look for. I did spot some rust stains on that side of the engine and was suspecting it to be a bad manifold but if there are no water passages I will take a closer look along with the mainifold to riser joint.
Thanks

 

[Fishermark]

Re: Manifold Replacement

I did spot some rust stains on that side of the engine and was suspecting it to be a bad manifold but if there are no water passages I will take a closer look along with the mainifold to riser joint.
Thanks

Bond-o is right of course, there is no water going into your manifold at that point. BUT - there is a core plug on the side of the block that is hidden by the manifold. That may be the source of your leak as well.

 

[John2037]

Re: Manifold Replacement

risers and perhaps mani's.... it sucks but if you see rust on the outside it's on the inside, but worse, and it's not a buying used problem, it's maintenance. From what we recommend where I work, for risers, is change every 3-4 years. If you don't change, I would buy some riser gaskets and inspect, if they're okay then you've wasted a few bucks, if it starts leaking water into the exhaust you could run into major problems. I would change the plugs too - a recent job sounds similar to you situation and the corrosion went from the riser all the way to the plugs.... all the plugs broke flush with the head

 

[Thomv]

Re: Manifold Replacement

I did run the engine over the weekend and could not find the leak. Everything was dry. What I did find is old rust stains directly below the hose inlet to the manifold. The previous owner might have tightened up the stainless steel hose clamp at this connection and never cleaned up the rust stains leading me to belive I had a leak. I will replace this hose and clamp because the hose feels crunchy.