Question 6 - Water in the Engine

From Bob Oyen:

I need some advice/help...

I'm getting water in one of my motors from the exhaust side.....

I can't tell if it's the manifold. the elbow, or the riser... Does the elbow usually leak? It's the lowest point, I would think it's the most likely culprit..... I have the V-Drive twin OMC V8's. Should I replace all 3?... Pretty spendy! ..........................................

Carl's Answer:

The same thing happened to me on two occasions on my 454 Crusader vee-drive installation. The first was in Desolation Sound, B.C. Canada. The seawater had rusted through the manifold and drained into the aft port cylinder causing a hydraulic lock. The engine would not rotate for starting. I removed the spark plugs and found sea water coming from the aft port cylinder. Fortunately it was not antifreeze solution because that would mean either a cracked block or a head gasket leak. I removed the manifold and found the hole. Fortunately, I was able to have a replacement manifold flown in and was able to install the new manifold myself. Removing the old one was easy, but to install a new one you need guide pins. They are simply 6 or 8 inch bolts with the heads cut off and a screw driver slot cut in the ends. You only need two. After sliding the new manifold on the guide pins, you secure the manifold with its own bolts and then remove the guide pins and install the last two bolts. I was out of Desolation Sound in two hours after the new part arrived. This all happened the year I bought my boat. The opposite manifold had rusted through just before I purchased the boat, so the seller had to replace it. This should have been a signal to me to replace the other one at the same time, but I was not aware of the rust-through problem with seawater cooled manifolds. My previous boat, an Owens, had freshwater (antifreeze) cooled manifolds. I have heard that saltwater cooled manifolds last an average of 10 to 12 years. This one was 13 years old.

The second leak I had was from the 90-degree elbow that connects with the rubber hose that connects to the muffler. It serves to mix the seawater with the hot exhaust. On my engine, the riser is integral with the manifold. Water was getting into the aft starboard cylinder. I discovered this when I was inspecting the spark plugs and one was wet and rusted. When I pulled off the exhaust elbow the inside where the seawater is supposed to mix with the exhaust was mostly rusted away. I suppose water was spraying back into the riser. I replaced both elbows.

If either of these is your problem, I would recommend replacing them all.

Dean's Answer:

Wet engine: First -- I don't know what you mean by the "elbow". Next -- a question. Do you have "fresh water cooling" (antifreeze solution a la autos), or "raw water cooling"? All us guys in the north have fwc. The difference is that with fwc, the antifreeze circulates through the engine only (and in later ones, the manifolds), and through a heat exchanger cooled with raw water (via a supplemementary "make-up" pump); whereas with rwc, the cooling water is picked up directly from outside the boat by the engine pump, circulated through the engine, manifolds and risers, and dumped overboard in the exhaust. Your boat being "older", I'd guess you have raw water in your manifold in either case.

The OMC engine configuration was designed for rwc, and the cooling water passed from the manifolds into the risers through small passages surrounding the exhaust gas passage. When they were converted to fwc, those passages were blocked off so the antifreeze solution could not go "up there", and the raw water was dumped into the risers via a couple of hoses coming from the heat exchanger.

There were several means to block the passages between the manifolds and risers, some of them pretty iffy. If you have fwc, that's the first place I'd look. Second place would be the risers themselves. Here in salt water land, salt-water corrosion in those relatively small cast-iron passages will block them within four or five years unless we take the risers off and clean them out every couple of years. (That's no fun.) Even then, they plug up eventually, and we run hot because we can't get rid of the cooling (raw) water. And then we replace them.

But, you have water in the engine, and you said it was in the exhaust area (I presume you find water in a cylinder and/or a wet plug), so plugging of the manifold passages probably isn't the main problem, unless the plugging adds enough pressure to make some other place leak -- especially if you have raw water in the manifold.

So --- since the only places water comes in contact with the engine exhaust is the manifold, and hooked to that, the risers -- that's where you gotta start. Try not to break the riser bolts off in the manifold. We have to juice ours up with WD-40 for a couple of days before we attempt to get them off. (And be sure to put anti-seize on them when you put them back.) If the risers are pretty elderly, I'd suspect the water passages are at least partially blocked. And the wall between the water passages and the exhaust passage can erode to nothing, letting them mix.

IF the risers look ok, then you gotta pull the manifold (s) and pressure test them.

If either raisers or manifold are bad, then you get to replace them. (You knew that). I've never lost a manifold. (Remember -- I have fresh water cooled manifolds). I still use the OMC-style riser, although OMC no longer makes them. I paid about $80 apiece for the last ones I got. If the manifold(s) were bad, I'd consider putting on Barr or Osko -- or some other brand. I suspect they're a couple hundred apiece.

And then, you get to consider whether to replace them on both engines. Oh, boy!

Hope this helps. There'$ no ea$y $olution to the problem. $orry.

Dean