exhaust manifold blockage

[jmarine225]

Hello all. I was just doing some routine maintenance going through my cooling system and found something unusual. First off I have a 93 OMC Cobra 5.8L. I removed one of the water lines that feeds into my manifold to check for any blockages in the hose or the manifold when I found a solid chunk of mud in the hose. Curious how that could happen. I then proceeded to clean out the manifold from the inlet with a wire brush, as good as possible to be sure of no blockages. Everything seemed clear but there was definitely some mud in the manifolds also. Tomorrow I will work on the riser before moving to the other side. I burned up an exhaust hose in the past and even though it's not showing an overheat on my gauge I guess I'm paranoid something may still be causing an overheat. What could be the cause of the mud in the there and will the cleaning of the manifolds and risers with a stiff wire brush be effective to clear any blockages? I plan on changing the manifolds in the off season as they appear to have had their time.

 

[jtybt]

Re: exhaust manifold blockage

I'm guessing you run around in shallow fresh water. I think it would be smart to back flush your whole cooling system just to be on the safe side. You might even consider popping out the freeze plugs to see if there's any mud or sand collecting.

There are quite a few boat engines destroyed every year from ingesting mud and sand that clog the cooling system.

 

[jmarine225]

Re: exhaust manifold blockage

Thats the weird thing. I have my boat moored in a slip on a lake and have never been in any shallow water. A mechanic said he flushed the whole system and it was clear. I had to actually take the hose off to get the mud chunk out. Besides that will brushing the manifolds with a stiff wire brush along with brushing the risers do any harm? I've been doing it hopefully to clear any blockages which may remain.

 

[futz]

Re: exhaust manifold blockage

What you think is mud is maybe rust. Ether way i bet them risers and mani's are original to the boat, Me i would over the winter pull them off you may be surpirsed what you find in the risers and maybe the mani's.

 

[jmarine225]

Re: exhaust manifold blockage

The risers are aftermarket so I know they are not the originals though I still don't know how old they are. I plan on inspecting them after these tornado/t-storm warnings. The manifolds are stamped "OMC" so they must be a few years old at least. They must have been at the least removed because the manifold studs appear to be new. My question though is will scraping the manifolds and risers with a heavy stiff wire brush be enough to clear any blockages till the end of the season? I pulled the hose off the manifold intake and heavily brushed the inside of the manifold and appeared to remove what I thought was mud, but I take it, was probably rust. I just don't want to burn up an exhaust hose again.

 

[a70eliminator]

Re: exhaust manifold blockage

If those are true OMC 5.8 manifolds then you will have a clean out plug in the rear where most of the mud sediment rust ect. will accumulate, take those plugs off and run your wire then flush with a hose attached to the front nipple.

 

[jmarine225]

Re: exhaust manifold blockage

yes I do have a plug with a cap on it at the end of my manifolds. Wasn't sure but it is safe to open that and blow water from a hose from one end and out through the other? I was afraid water may get into the engine but then again, water from the water hose goes into the manifold that way.

 

[a70eliminator]

Re: exhaust manifold blockage

Water will not get into the engine if the manifold is good, and we are dealing with good manifolds here I believe, and yes remove that clamp and wiggle off the rubber cap, it's a tight squeeze but it will come off and be reusable, I'm going to bet that you'll find it totally plugged with the same mud, dig it open then clamp a hose onto the front and run a little water through as you probe around the inside from the rear, the water will help flush out the debri.

 

[jmarine225]

Re: exhaust manifold blockage

One more thing. Just to rule out the possibility of a blockage in the manifolds, if I can push a brush from front to back with no problem and nothing coming out then my manifold is not blocked and water should flow freely through them correct? Hopefully so then I'll move on to my risers and clean them up.

 

[a70eliminator]

Re: exhaust manifold blockage

I don't know if you could push a brush through a new one, they are double wall construction water passages go around the tubes, I would love to see a cross sectional drawing of one.

 

[jmarine225]

Re: exhaust manifold blockage

Since it appears you have the same engine as me maybe you can give me a solid answer on this question. If my temperature gauge is reading normal (160 with a 160 t-stat) do I still need to be concerned about the temp of my risers or manifolds? If I had a blockage in my manifolds I would think my gauge would riser since the water wouldn't be able to pass through the manifolds efficiently. I just don't want to have to run the boat and constantly be concerned about the the riser temps and have to keep checking them.

 

[KRH1326]

Re: exhaust manifold blockage

When I started my project boat, I didn't want to dump 800 bucks for a whole new exhaust setup, untill I had rebuilt the engine and drive, AND want to put a season on the boat before deciding it's a keeper, and dumping $ into it.

BUT, I did pull the manifolds and risers. I removed all ports and freeze plugs etc. I boiled them in an old turkey deep fryer ( with water- not oil), then I turned my pressure washer with red tip loose into the water passages. The crap that came out would choke a horse. I closed all the ports back up and ran considerable pressure through it. I have still got beautiful flow when running. No more burnt rubber.

Good Luck

 

[jmarine225]

Re: exhaust manifold blockage

I plan on a full cleaning or replacement in the off season but am concerned about it now as stated in my previous question. If my gauge is normal do I need to be concerned about the temp of manifolds and risers or would that show up on my gauge if they were blocked not allowing a normal flow of water? I would think if the t-stat reading is normal then at the least my manifolds could not be blocked because then that would have an effect on the t-stat reading since that is where the water is coming from.