Hydrolock, swim platform, riser height and static water line question

[Augoose]

Good afternoon all,
first I apologize for the length of this post. I feel its important to add background details and hopefully it will make sense the more you read.

In 2019 I started a thread about my 1999 Chris Craft 200 with VP 5.0 and SX-M drive having to do with water being ingested into several cylinders on both sides of the engine. The general consensus at the end of the thread was that I needed taller risers, however I've since measured my riser height and I'm at 15". More about that below.

To quickly back up for a minute, in 2016 I installed a swim platform on the back of my boat. I think it is important to note that I did not have any water ingestion issues (that I know of) between 2016 and 2019.

My current problem began one day in 2019 after we were anchored for 2 hours off an island. We experienced probably the worst chop we had ever been through while anchored - 3 foot swells at times on our lake. No one was sitting on the swim platform. After swimming, we got back on the boat, started the engine and idled away from the beach for about 10 minutes. All was normal. After about 10 minutes, we opened the throttle up and for about 2-3 minutes, all was good until the engine started missing - like I was losing spark. We slowed back down, let the boat idle again, and then opened up the throttle once again. Engine was fine for another 10 minutes or so at which point and while on plane at about 28 mph, the engine instantly died. A wave of water hit the back of the boat and then I had water in my cylinders for the first time that I knew of. Fast forward through dealing with the water ingestion itself, I did some troubleshooting and replaced everything I could think of having to do with spark, electrical and fuel delivery. The following spring I did a few water tests. The boat seemed to run fine and I could not reproduce the sudden engine stop.

Following that, we started taking the boat out in the summer months, anchoring and swimming again. I then began observing issues with what I believe to be small quantities of water getting into the cylinders occasionally when the boat is anchored in chop (bow anchor with bow towards wind and chop). The frequency of symptoms was very inconsistent in that sometimes the boat would start and run fine while other times the boat would take a minute to start and would die instantly under throttle if I tried to depart before letting the boat idle a bit. Best I can tell, I continued to have water entering the cylinders when anchored in chop or while people are sitting on the swim platform with at least some wave activity from passing boats. It doesn't happen every time, only occasionally which makes it really hard to troubleshoot.

When I think water has entered the cylinders, symptoms include the engine taking about a second or two longer to start after engaging the starter (vs starting immediately which is normal for this boat), at which point the boat idles but not as clean as it normally would. If I give the boat somewhere between 1/2 to 3/4 throttle right away, as if pulling a skier, the engine will respond to the increase in throttle for just a brief moment and then immediately stop as if I lost all spark. The boat will then typically start back up again as if nothing happened.

Now, if all the above conditions are the same (anchored in chop, folks on the swim platform, etc) and I notice that the engine takes a second or two longer to start (which is my indicator that something is wrong) I'll then let the engine idle for about a minute, When I let it idle for a minute or more, I've never noticed a loss of power during a following hole shot.

Thinking back to the beach incident during the previous year and assuming with all that chop, I must have taken on water into the cylinders while anchored. However, if that had indeed happened (since it appears to be happening now) I can't explain why the boat idled for the better part of 10 minutes after leaving the beach that day and then died suddenly, beyond assuming the boat was suffering from some sort of unrelated electrical or fuel delivery issue. I also can't explain why only after the beach incident, I now seem to be having issues with water getting into my cylinders.

Maybe my boat was the last 1999 model to still have exhaust flappers and the flappers failed after the beach incident and coincidently now I'm starting to have issues with water ingestion? Or do my problems detailed below somehow related back to what happened at the beach? How can chop cause water to enter my cylinders now when it didn't at the beach since the boat ran for 10 mins without a problem? And since the swim platform has been on the boat since 2016, how could that be contributing to my water ingestion issues now? I feel that my sudden loss of engine was related to a now-resolved electrical or fuel delivery problem, as I've put nearly 100 hours on this past summer with no residual symptoms beyond what appears to be occasional water ingestion while anchored. Again, if the boat is left to idle for a minute or two following being anchored in chop, I have no issues whatsoever. If I anchor in chop, start the boat and immediate ask for throttle within say 10 seconds, it will likely die instantly while getting on plane.

I typically park the boat on the trailer when its not in the water but occasionally I'll leave it in the water overnight at a dock. When I've done that and come back to the boat the next morning, the engine starts likely it normally would considering its cold and hasn't run since the day prior. I can't replicate an immediate hole shot there of course because I must idle out of the now wake zone, but I feel as though the boat sitting in calm water no matter the period of time has never produced the symptoms of water ingestion above.

Furthermore, repeated start/stops while tubing or pulling skiers for example without mooring or sitting in chop has never produced a long starting period as detailed above or a rough idle, nor has it caused a loss of power or engine cutout at the hole shot. It seems that the above symptoms ONLY happen if the boat has been moored or anchored in chop or people have sat on the swim platform for an extended period of time with some wave activity. We have driven the boat for about 15 minutes, stopped for an hour in calm water, and then started and ran the boat again with no issues.

I'm wondering if the couple of seconds of occasional rough idle after being anchored in chop is the engine working out small quantities of moisture in the cylinders. If I give the engine a minute or two at idle, the moisture is worked out and then the boat runs well even during the hole shot. However, if I don't let the boat idle as long and immediately increase throttle I wonder if I'm getting a loss of spark/combustion because the engine can't deal with the increased load when there is still a bit of moisture in the cylinder?

As stated above, I measured my riser height and the top of my risers are a solid 15" above the waterline with a full tank of gas and people in the boat. I need to verify that same measurement with one or two people sitting on the swim platform specifically, but I would have thought that the 15" would have given me a enough fudge room - maybe not?

I was about to purchase the next taller riser, however I would need to trim a couple of inches of fiberglass off each side of my engine bay to make the taller risers fit. Before I did that, I wanted to be as sure as possible that riser height is in fact my issue- that's why I put all the details above. Could it be anything but riser height? Why was I ok for nearly 3 years after getting the swim platform? Maybe my boat had exhaust flappers and they are now toast and are allowing water to be pushed up while anchored in chop?

If I had a leaking manifold or riser gasket or a crack somewhere in the water jacket, I suspect I'd have water in my oil, correct? My oil looks great and the level has not increased at all.

Is there any other way for water to get into the cylinders but for the exhaust?

Sorry again for the long winded post - just wanted to include as many details as I could.
Thanks!

 

[Lou C]

If your boat is a 99 then it may not have flappers, I think V/P discontinued them around that time. V/P also had trouble with their manifold to elbow gaskets and they had been revised a few times. Have you seen any rust stains at the joint between the manifold & elbow? If so then the gaskets could be bad letting in small enough amounts of water to cause a misfire then when the engine dies the water rushing against the transom might hydrolock it. Personally I thought V/Ps decision to remove the flappers was ill advised. Merc engines have always had them and I have the same style V/P used to use on my Cobra and have never had water in cyls or a hydrolock. If yours never had the flappers I’d remove the exhaust bellows and fit a flapper valve like inboards use on the exhaust outlet of the gimble housing. And, do remove the elbows to check for bad gaskets.

 

[Augoose]

Thanks Lou. I looked for rust stains on the sides of the manifolds below the riser/manifold seam and it all looks clean.
If the elbow to manifold gaskets were leaking while the engine was running, would the the pressure from the moving exhaust keep water from entering the cylinder and only allow drips to enter when the engine was not running?

 

[alldodge]

Don't see your issue has anything to do with water in the cylinders. If it ever hydrolocked (running) it would be rebuild time

What motor is it? GL, Gi, other, serial number would be great

 

[Augoose]

Thanks alldodge,
Maybe hydrolock is the wrong term.
When it stopped coming back from the beach and the wave hit the back of the boat, I tried to start the engine and it sounded awful, so I was towed in. I had a significant quantity of water come out of all of the rear cylinders. I sprayed WD-40 in each cylinder immediately, changed the starter and inspected the flywheel (as I had tried to start the boat with water in the cylinders). Three oil changes later and all the water was out. I was very lucky.
During one of the subsequent events the following summer where the engine was turning over and not immediately starting after being anchored with heavy chop, I again removed the spark plugs and observed a bit of water spray out while engaging the starter. I had a paragraph dedicated to that in the initial post, I must have accidentally deleted it.
The motor is the GL -
- SX-M drive 1.51 gear ratio
- PN: 3868890
- SN: 4112059776
- 5.0 GL Volvo Penta Engine PWTR
-PN: 3868944
-SN: 4110175119

We got to the point last summer that we wouldn't sit on the back of the boat at all and we'd avoid areas with chop. When we followed those "rules", we never seemed to have an issue. When it was choppy - we seemed to have starting/running issues every time. I did not pull the spark plugs every time it failed to start immediately but the one time I did as mentioned above, it appeared to have water in the cylinder.

 

[Lou C]

I looked up your engine in the V/P parts diagram on this site and it did not come with flappers. I’d consider removing the exhaust bellows and installing an exhaust flapper on the gimble housing where the exhaust bellows would normally attach.
I’d start with that and if it solves the problem then great if not I’d fit the taller elbows.
Just measure the diameter of the exhaust opening on the gimble housing and get an external exhaust flapper to fit. That will keep water from rushing up the Y pipe and correct V/Ps engineering mistake.

 

[Augoose]

Thanks Lou. Is that a VP part or are you talking an aftermarket part?

 

[Lou C]

Aftermarket. Like what you see on inboard boats with thru the transom exhaust.
The OMC/VP exhaust bellows is retained with a clamp on the gimble housing end and a snap ring in the pivot housing end. So to remove it you have to pull the drive get a snap ring pliers and remove that end, then tilt up the pivot housing and remove the clamp and pull off the bellows from the gimble housing end. Then install the inboard style flapper.
I bet the weight of the swim platform is the culprit. But each boat is different. With the standard OMC Cobra style flappers I have never had water up the exhaust in all the years we’ve had this boat. VP modified the OMC Cobra design when they designed the SX series and felt the flappers were ineffective in preventing water intrusion so they discontinued them in 99 but here you are no flappers and water intrusion!

 

[Augoose]

The exhaust flapper solution is tempting, however if its water intrusion due to the added weight, I do wonder why I didn't have problems immediately after installing the swim platform?
You also brought up a good possibility about water leaking past the exhaust riser gaskets.
If the gaskets had failed, would the failure be apparent if I pulled the risers off and looked at them? Would there be rust stains on the gasket material? I also wonder why I seem to be able to go days and days on flat water with no issues at all. Wouldn't failed riser gaskets cause issues all the time?

 

[Lou C]

There would be rust stains in the bottom of the exhaust gas passage of the exhaust manifold. Inside the exhaust gas passage there should just be dark grey/blackish deposits, no rust.
The other questions are difficult to answer.

 

[alldodge]

If the riser gaskets are leaking you would be able to see a path on the gasket where its not sealing. As Lou said may also see rust

I'm seeing more weight is probably the issue. Kids growing up, and could also be the boat is soaking up some water along with the chop. Happen to see water on top the swim deck from the chop? Swim deck attached with bolts below the water line maybe?

Either way the boat is a bit lower and I would go with 4 to 6 inch high risers if you have the room

 

[Augoose]

Thanks alldodge. I'm going to pull the risers and inspect for signs of leaks.
Water does not make it on top of the swim platform and instead the platform presses down on the surface of the water and creates a spray of pressured water through the vents in the platform itself. So, water sprays up a bit, like a whale's blowhole. I had thought that as the boat is rocking bow to stern, that the outdrive is scooping water and the pressure created by the scoop is allowing water up and through the exhaust?
The mounting bolts for the platform sit well above the water line and I've not seen any indication of water absorption anywhere around the transom. I looked back at photos of the boat sitting in the water over the years and the water line has always sat equal to a painted trim line on the stern of the boat - still there now. The kids are getting bigger (9 and 15) so maybe we have crossed the limit so to speak.
My risers are the standard 7 3/4" height. VP listed their "tall" risers at about 11 1/4". I found this morning medium height risers at 10 3/4" by Basic Power industries.
I need to measure available clearance again in the boat to see if I could squeeze in the medium height risers. It would be close.
I appreciate all the info from both of you gentlemen. Before I go cutting into fiberglass I wanted to be sure that I wasn't missing another avenue as to how water was getting in.

 

[Lou C]

If you can post up a pic of the boat in the water specifically the transom so we can see how high up the water is against the transom mount assembly.
Here’s mine...the Cobra transom mount & the Volvo SX mount are nearly the same. The cat is fake and keeps birds from using it as a toilet lol!

 

[alldodge]

Yep, VP doesn't use risers like Merc, it uses taller elbows

 

[Augoose]

Sorry, I got risers intertwined with elbows.
Here's my boat sitting in the water with everything it normally would have on it except for people. I also found a close up of the transom assembly before we had the platform. My wife (petite) is sitting on the back. Doesn't seem to be a significant difference in how the boat sits in the water with and without the platform based on where the waterline meets the green trim. I'd estimate the platform weighs about 110 lbs.


Here are my elbow gaskets from this morning. There's no line of rust that I can tell on the gasket, however there are what I would call specks of rust here and there inside the throat of the elbow. The opposite end of the elbow which connects to the exhaust tube leading to the lower unit looked awful though. I suspect that any signs of rust there had to come from water coming up through the exhaust or is there a level of rust which is to be expected due to moisture in the air and humidity? Should the interior of the elbows be completely void of any signs of rust whatsoever? Overall it is black and sooty. I also pulled the center spark plugs directly below the joint and there were no signs of rust on them. The plugs were replaced following the beach incident. I will be at the least changing the manifolds and elbows as it is beyond time.

What is the consensus on the quality of aftermarket manifolds and elbows? Get what you pay for or same as OEM?






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[alldodge]

The mans and elbows don't look bad, sealing surfaces could use a flat file or other maybe. The elbow exhaust end is erroded some, and if you were having trouble with reversion then I would think more about it at that location. Appear to be fresh water

Boat list 2750 lb dry weight. Add trailer (600 for single axle), gas, gear and cooler. If there is a truck stop nearby with a scale, run it over. Disconnect trailer and make sure its sitting on one of the sections by itself

 

[Lou C]

I agree I might want to replace those elbows to be on the safe side and that also gives you the opportunity to upgrade to taller ones. Even if you need to do minor fiberglass work to achieve that goal it’s worth it. Keep the mind that water in cyls and hydrolock will destroy and engine sooner than later. I’d also consider replacing the exhaust bellows with the inboard style flapper. Taller elbows + exhaust flapper should solve this problem for good. I still can’t fathom Volvo’s flawed logic in removing flappers and then doing nothing to prevent water rushing up the exhaust. Someone else on the OMC forum had a similar boat and problem, the y pipe must have been replaced with a Volvo pipe and there were no flappers. Standard height elbows same problem you had.

 

[ripjmk]

I agree I might want to replace those elbows to be on the safe side and that also gives you the opportunity to upgrade to taller ones. Even if you need to do minor fiberglass work to achieve that goal it’s worth it. Keep the mind that water in cyls and hydrolock will destroy and engine sooner than later. I’d also consider replacing the exhaust bellows with the inboard style flapper. Taller elbows + exhaust flapper should solve this problem for good. I still can’t fathom Volvo’s flawed logic in removing flappers and then doing nothing to prevent water rushing up the exhaust. Someone else on the OMC forum had a similar boat and problem, the y pipe must have been replaced with a Volvo pipe and there were no flappers. Standard height elbows same problem you had.

I don't see how an external exhaust flapper would work on a SX-M outdrive? On my 2005 SX-M the exhaust is open to the underneath of the transom plate outside before the exhaust bellows connection. The exhaust gas only goes through the bellows when the prop creates a suction. At low speeds it bypasses the gases straight to beneath the transom plate.
Or am I missing something? I'd really like to install a backflow prevention device but as yet I've not found one.

 

[tpenfield]

You seemed to be focused on water entering the cylinders via the exhaust . . . Maybe it is not.

You don't seem to be getting a lot of water, otherwise you would have experienced a hydrolock and the resulting damage to the engine.

Perhaps the water source is within the engine . . .

Head gasket
Valve guides
Intake manifold

Maybe a compression test, a cylinder leak test, and a cooling system pressure test are in order. (I did not see any such info above unless I missed it)

Double check the 15" height on the height of the elbows above the water line. It seems high enough to avoid water ingestion, but not sure of the spec. (FWIW - my boat - with added swim platform - has the elbows at about 12" above the water line, the spec is 13", so I'm a bit shy of the spec.)

The challenge with added swim platforms is that you can have more people at the stern of the boat and at a point further aft. So this can make the stern sit lower than the boat builder anticipated in configuring the exhaust. It does not seem like you have that issue though.

I would run the tests and if all good, see about adding a riser between exhaust manifold and elbow.

 

[Lou C]

I don't see how an external exhaust flapper would work on a SX-M outdrive? On my 2005 SX-M the exhaust is open to the underneath of the transom plate outside before the exhaust bellows connection. The exhaust gas only goes through the bellows when the prop creates a suction. At low speeds it bypasses the gases straight to beneath the transom plate.
Or am I missing something? I'd really like to install a backflow prevention device but as yet I've not found one.

OK if you look at the idle relief ports under the transom mount, they are pretty small. The exhaust bellows on the other hand is like 3 1/2" in diameter, so the amount of water that could rush in from the bellows is a good deal more.