4.3L 4.3LX Mercruiser engine has water in the exhaust manifold.

[jgr316]

I removed the exhaust risers and looked down into the manifold and saw water inside. I removed the manifold, turned it over and filled it with water in order to test for cracks or leaks. The water level never dropped and remained full. Does this indicate that the manifold has no leaks or do the leaks only manifest themselves under motoring conditions? Obviously there is a leak somewhere since I observed water in the manifold as soon as I removed the riser, but I am wondering if it is the manifold and riser leaking or simply just the gasket. It is a 1996 engine and I am not sure if they are the original manifolds and risers, either way it may be time to replace them. My question is "Is there a way to definitivly test the manifold and risers ( I have heard of using acetone) or do I just need to go ahead and spend the money on new ones."

 

[Bt Doctur]

Did you bother to drain the manifold before you removed the riser?

 

[Watermann]

What problem were you having that made it necessary to remove the riser?

 

[NHGuy]

Reason he asked whether the exhaust was predrained is cause when you take off the riser the left over water could have fallen in to the exhaust.
But since it's apart go to the stickies at the top of the forum and follow the tutorial on testing the exhaust for coolant leaks.
You could have one of a few scenarios. Perhaps there is corrosion in the riser or exhaust manifold water jacket, perhaps there was a poor seal between the riser and manifold. Did you inspect the old gasket for tracks when you split the two parts?
Pull spark plugs and spin over the motor with the starter, with kill lanyard detached so it won't have spark. Watch the spark plug holes for any water being ejected. If you get any, dry out the cylinders and oil them. Let us know what happens, OK?

 

[jgr316]

The manifold was drained and the riser had no residual water in it when I removed it. I will follow the tutorial you suggested to test for coolant leaks, as well as trying to spin the motor to see if any water is ejected from the cylinders. The gaskets didn't seem to have any tracks, but did show a few signs of wear. I very much appreciate your assistance and will keep you informed NHGuy.

To answer your question Waterman, I was having trouble getting the boat to start when it was in the water. It seemed to start ok when it was on the trailer in the driveway, but after cruising on the water for a few minutes and then turning it off and sitting for no more than 20-30 minutes it would refuse to start. Obviously this could be caused by a number of factors, but I had read that a leak in the manifold or riser could be to blame and have also read that Mercruiser engines have a poor reputation when it comes to quality manifolds and risers. Therefore I decided to begin troubleshooting there since both the riser and manifold are fairly easy to remove and inspect. I also inspected the coil and found a significant amount of build up inside of the boot wire which leads to the distributor. I assume it is dielectric grease which a previous owner may have gotten overzealous with and used too much (because it was caked in there pretty good) , which could also play a significant role in the motor failing to start.

 

[HT32BSX115]

I removed the exhaust risers and looked down into the manifold and saw water inside.

Howdy,


Welcome aboard!

Well it's a pretty valid question to ask if you drained the manifold prior to pulling the risers.

When you're operating normally, the water level in the manifold\riser combination is well above the gasket....literally all the way to the highest point of the riser water jacket. When you shut down, the level will drop, but not fast enough to prevent *some* from getting past a leaky gasket before the level drops below it. (if it is fact leaking)

If you have a crack in the riser, the same thing will happen until the water level drops below the crack in the riser etc,

Once you got it apart, if they're not severely rusty inside the water jackets, and the sealing surfaces are nice and clean [and FLAT], just replace the gaskets and try again.

If there's significant rust in the water jackets, they're really old, salt water manifolds and risers, consider replacing them.


Cheers,


Rick

 

[jgr316]

There is not a significant amount of rust inside of the riser or manifold, I have seen photos online of some in really bad shape and mine are nowhere close to that. I'm thinking it was just a bad gasket or maybe I didn't do a good enough job of letting the manifold drain completely before removing the riser. I tried turning the engine over with no spark plugs and I did not see any water expelled from the cylinder so that is a good sign. I'll install new gaskets, get some new spark plugs, and clean the buildup and corrosion on my coil connection and see if that fixes my original problem of not be able to start the motor while it is on the water. Thanks to everyone for their input and I will keep you all informed.

 

[HT32BSX115]

You're probably fine then.

I had a similar problem with my former OMG 460 King Kobra.

I had riser gasket leaks in both sides and immediately after shutdown, like when picking up a downed skier etc, if I tried to restart the engine, I would experience a brief hydrolock....If I tried to crank it a couple of times, it would act like the starter was failing/dragging or the battery was low etc...........

If I waited for more than about 30 min, the engine would crank right up! (presumably, after 30 min or so, the little bit of water would leak right by the rings and drop down into the crankcase........since the engine was hot and I'd run it afterwards, that little bit of water didn't last long in the oil)

When I pulled the risers, I noticed evidence of water in the both sides and when I pulled the heads, there was light corrosion in a couple of cyls on both sides.

I was going to replace both the manifolds and risers, so I tried a little exercise with a belt sander. I was able to "clean-up" both riser and manifold surfaces to the point where I had bright shiny metal for the gaskets....and they checked out pretty flat.....

If you try that, you MUST be careful not to take too much metal off and you need to maintain the flatness of the surfaces. If you're not sure you can do it, find someone with a vertical milling machine and have them straighten them up. (although if you have to pay a machine shop to do it, it might be better (and cheaper in the long run) to just replace them

Unfortunately, there were no OEM manifolds to be had for the 460. AFAIK, no one makes them nowadays either. (there's an adapter to put 454 manifolds on a 460 but I know no one that has done that...... they weren't available when I had the 460 in my boat and I now have the 454/BravoIII)

Just do a little block sanding of the surfaces to clean them up, check them with a straight-edge and replace your gaskets........as long as they're not cracked, you'll be fine!


Cheers,


Rick
,

 

[jgr316]

I was able to clean the surfaces with just a piece of sandpaper and sanding by hand. Just by doing that I was able to get a shiny surface which checked out well with a straight edge. I plan to go get new gaskets and spark plugs tomorrow and install them. Hopefully that will solve my problem. Thanks again for all your help and I will keep you informed!