Water in the engine?

Several ways, but most common are through a failing or improperly installed exhaust system. The risers rust/corrode on the inside and eventually the water jacket fails and allows seawater to drain into the cylinders, usually in small amounts after the engine is shutdown, water sits in unused engine and rusts valves etc. Some inboards with older log style mufflers had problems with water coming back through the exhaust and into the engine. Also, on a stern drive, the exhaust flappers (one way valve that lets exhaust out, keeps water from coming in) can fail and allow water to come back into the engine via the exhaust. Most of the time there is a special condition that allows the water to backup through the exhaust, a combination of improperly installed system plus conditions such as backing down in a following sea or quickly coming off plan in such a way to allow the stern get low and allow the water in. Other than failed risers, it's not what I would call common, you hear about it because it usually causes a big repair bill. I've been boating for my whole life (a long time) and have owned half a dozen boats with all motor types, I have never had an exhaust / water intrusion related problem. But it can and does happen.
 
I had an intake manifold rust through last summer and it killed a 5.7 while it was running, put water in all 8 cylinders. Engine had fresh risers and manifolds that same spring but was old and something else ate through. Went with FWC closed cooling on new engines.
 
I've been through this twice now, 2 different boats, both times exhaust manifolds failed and allowed water into cylinders on my stern drive Merc. Both times I flushed engine out with kerosene after draining oil, then changed oil after 5 minutes of running, then after 10 minutes of running, then after 20 minutes of running. Both times I saved my motors and they went on to give many years of service. They tell me I was LUCKY!
 
SloBurn said:
I've been through this twice now, 2 different boats, both times exhaust manifolds failed and allowed water into cylinders on my stern drive Merc. Both times I flushed engine out with kerosene after draining oil, then changed oil after 5 minutes of running, then after 10 minutes of running, then after 20 minutes of running. Both times I saved my motors and they went on to give many years of service. They tell me I was LUCKY!
Click to expand...
You were very lucky that you didn't bend some valves or a rod.
Water doesn't compress. Most times the water gets in to the cylinder(s) and the owner doesn't know it so he attempts to start it up. When he realizes the starter stopped spinning the motor the first thing they usually think is the starter is bad.
Seen and heard this exact scenario a bunch of times over the years.
A close friend had an auto repair shop and bought a bunch of boats off of customers over the last 35 or so years that this had happened to. The story from the owner was almost always the same, and they just wanted to get out of their non running boats.
He'd put a motor in a boat and use it for a season or so until he got a good price and then he'd sell and wait for the next deal to come along.
He's the only guy I know that made money on just about every boat he ever owned. I don't think he's ever boat one with a good motor.
 
Not a feel good story for me but I bought the boat last spring, had steering pin leaks on both assemblies, mechanic replaced both. Then both motors ingested water, replaced both long blocks. Insurance company had surveyor present when manifolds were removed and they covered the long blocks under the premise of "water reversion". Mechanic still stands by it was the manifolds. Conversation with surveyor stated the flappers were installed correctly but the new Merc flappers were not compatible with the old risers. Not sure but happy with the insurance check, dulls the pain slightly.
 
I just went thru this this weekend.
Was replacing spark plugs 4 of them came out with rust on them. 2 from each motor.
Removed the risers found the gaskets between the spacer blocks were leaking.
I probably could have just replaced the gaskets and risers but did manifolds.spacers and risers on both Engines.
Both motors ran fine thank god when i ran them after replacing everything.
I am going to replace the spacer gaskets every 2 years and check the spark plugs at the end of each season.
 
I bought my boat with a bum starboard motor due to a manifold failure. I think just R&R heads on that motor would have been fine however I opted to replace both engines. The service adviser at the shop made sure that exhaust resonators were installed.

Here is a copy/paste about resonators - now these won't help when a manifold or riser fails however the true ingestion issue come from low RPM and aggressive cam. The HO motors have a very aggressive cam and can create a vacuum at low RPM which would cause exhaust water to be sucked back in. I don't know all the science behind it, just repeating what I was told by the engine manufacture. I was also told to get the tallest riser spacers you can fit as this will help against sucking water back in.

EXHAUST RESONATOR
The exhaust resonators (provided with the engine package or available separately) are designed to provide increased resistance to water ingestion due to the tuning effects of the exhaust system. Quicksilver resonators are designed to break up the exhaust pulses.

CAUTION!​
​
Avoid severe engine damage. Water ingestion by the 454 and 502 cid (7.4Land 8.2L) engines may occur in some instances without the use of speciallydesigned exhaust resonators. Install exhaust resonators in the exhaust system when specified.

IMPORTANT: Exhaust resonators must be installed on 7.4L MPI, 454 Mag MPI and 502Mag MPI Models of sterndrive engines with through the transom (or through the hull) exhaust

On 454 and 502 cid (7.4 and 8.2L) sterndrive engines using through the transom or hull exhaust systems, special care must be exercised in system design and construction to prevent an adverse tuning effect on engine exhaust output.
 
I have just gone through this with my 370 and this is what I've discovered.
1. Most Mercruiser big blocks suffer from reversion where water is drawn back up the exhaust by a negative pulse wave created by exessive cam overlap.
2. The standard riser height is insufficient and water can and does flush back up the exhaust when you come off the plane.
3. some non standard manifolds (mine were stainless steel Hitec's ) can excerbate the reversion problem.
4. On my 370 the Helm.cockpit lounges and generator are all on the stb side ,add a bunch of guests on those lounges and the stb side starts to get
pretty low in the water.

At the moment I'm looking at fitting the 8.1 manifolds with the HO stainless steel risers for some extra height and also converting the manifolds to closed loop cooling.
Also fitting resonators and turbulators and hoping hat fixes it.
I'm also toying with and idea that would allow the 8.1 stainless risers to be bolted onto the standard 7.4 manifolds thus allowing the manifolds to be cooled in the closed loop.
 
Doc
Our boats were notorious for this problem before the 8.1s came around. When shopping, I stayed away from all 380s of this style with 7.4s and log mufflers. Many were repowered, many boasted "rebuilt" 7.4s. Problem was the reversion as described by Brad above, when combined with underwater exhausts and horizontal log-type mufflers.

I believe the problem could have been solved with just water-lift mufflers to replace the log-style but not sure.

What does your '99 have (in terms of mufflers)?
 
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