1988 Malibu Skier, 5.7 Merc Hydrolocking...next steps

[kingderzelas]

Hey everyone,

Im still very new to the hobby of boating and this is my first time posting, and tried to do as much research on the forum here and elsewhere before going forward. So far I have bits and pieces to put together but want to make sure I'm seeing the whole picture before moving forward. Long story short I took the boat out two days ago and it was idling pretty high which caused it to start deiseling and then it hydrolocked. I got home and the cylinders in my left bank were full of water. Based on initial research I took the spark plugs off, and cranked the motor to expel as much water as I could. Then plan was then to leave it uncovered with the doghouse open to let as much moisture evaporate while I figure out my next steps. I know I for sure need new spark plugs, but beyond that Im not sure what my next steps should be.

• Do I have to change the oil even though water only made it into the cylinders? From my understanding the piston rings should theoretically keep water from seeping into the oil.
  • If I do have to change the oil, what oil and filter should I be looking for? Ive a lot of debate on this so I guess just tell me if I'm ok to use Royal Purple 15W-40, or Mobil 1 15w-50. 
• Do the cylinders need to be 100% dry before putting in new spark plugs and attempting to run it? When I crank it I still get some puffs of moisture coming out.
• Once the process is done, how do I go about fixing the high idle so this doesn't happen again? Long story short I ended up replacing the spring piston thing in the carb that controls acceleration? For some reason when I bring the throttle to neutral the piston doesnt fully decompress so it leaves it revving too high. Old piston didn't have that problem. 

If I missed a thread where I can find these answers please point the way, and many thanks in advance for any tips or advice!

 

[solorex]

Um... where to start.  You're high idle likely has nothing to do with the fact that you have water in your cylinders.  Sounds like your manifolds are rotted out.  You will need new exhaust manifolds, take those off, inspect and replace.  You may have got lucky (hard to say); hopefully you haven't bent anything but yes you're going to have to change the oil, most people use some sort of multi grade diesel oil.  I was using Rotella SAE40 until it was unavailable.  But what oil you use at this stage doesn't matter, you just need something fresh in there and you really need to see if you hurt your engine.

[kingderzelas]

12 minutes ago, solorex said:

Um... where to start.  You're high idle likely has nothing to do with the fact that you have water in your cylinders.  Sounds like your manifolds are rotted out.  You will need new exhaust manifolds, take those off, inspect and replace.  You may have got lucky (hard to say); hopefully you haven't bent anything but yes you're going to have to change the oil, most people use some sort of multi grade diesel oil.  I was using Rotella SAE40 until it was unavailable.  But what oil you use at this stage doesn't matter, you just need something fresh in there and you really need to see if you hurt your engine.

I've seen that exhaust manifolds are likely causes of hydrolocking, but how would they cause a high idle? I can manually move the lever that controls the acceleration on the carb to neutral and the boat idle'd just fine, but now with the new part it doesn't return to neutral properly.

[solorex]

15 hours ago, kingderzelas said:

I've seen that exhaust manifolds are likely causes of hydrolocking, but how would they cause a high idle? I can manually move the lever that controls the acceleration on the carb to neutral and the boat idle'd just fine, but now with the new part it doesn't return to neutral properly.

Step 1: exhaust manifolds, or find out why you have water in your cylinders.  Way more of an issue than your high idle

Step 2: deal with your high idle.  Without pictures it's hard to tell.  If the throttle mechanism is OK on the carb, then your throttle cable maybe worn out, or check at the throttle control all sorts of things can happen there.  A common culprit on these older boats is that the brass bushing that holds the cable wears out and needs replacement.  They are held in with cotter pins.

[drh]

I could see it being a possibility that if the dieseling caused the engine to rotate backwards momentarily it could have sucked water in through the exhaust ports and caused the hydrolock.

What part did you replace on the carb exactly? The acceleration pump spring? And if you disconnect the throttle cable you say it idles correctly?

[kingderzelas]

4 hours ago, solorex said:

Step 1: exhaust manifolds, or find out why you have water in your cylinders.  Way more of an issue than your high idle

Step 2: deal with your high idle.  Without pictures it's hard to tell.  If the throttle mechanism is OK on the carb, then your throttle cable maybe worn out, or check at the throttle control all sorts of things can happen there.  A common culprit on these older boats is that the brass bushing that holds the cable wears out and needs replacement.  They are held in with cotter pins.

From what Im understanding, I believe the high idle is the actual cause of why water is in my cylinders. I believe the high idle caused the motor to diesel, because when I checked later that day I saw my right (as you stand at the back facing front) exhaust flap completely sucked in. Only way it could have done that is if the motor dieseled and caused a strong enough vacuum for it to happen. Ill check the bushing.

4 hours ago, drh said:

I could see it being a possibility that if the dieseling caused the engine to rotate backwards momentarily it could have sucked water in through the exhaust ports and caused the hydrolock.

What part did you replace on the carb exactly? The acceleration pump spring? And if you disconnect the throttle cable you say it idles correctly?

It was the accelerator pump spring that I replaced. That lever that directly pushes down on the rod in the pump spring, it doesnt fully come all the way back up anymore once I bring it back to neutral. So I have to press on the back side of that lever to fully depress the spring and once I do the boat returns to normal idle. Im trying to get some pictures uploaded but for some reason the link I use to host the images doesnt work here. Ill try to find another way.

[drh]

I'm not really familiar with Edelbrock/AFB style carbs but I think I understand what you're describing - the accelerator pump rod is holding the throttle open. The next question, of course, is why did you replace the spring and was it doing that before replacement? 

[kingderzelas]

1 minute ago, drh said:

I'm not really familiar with Edelbrock/AFB style carbs but I think I understand what you're describing - the accelerator pump rod is holding the throttle open. The next question, of course, is why did you replace the spring and was it doing that before replacement? 

Im not familiar with those terms either, I know I have a Rochester quadrajet. Here is a link to a stock image with a circle around what I'm talking about. It was not doing this before, but I replaced it because I bought a carb kit to replace the gaskets and it came with a new spring pump so I figured why not. This is my first time ever having to deal with a carb so the importance or function of some pieces are still foreign to me.

[drh]

First thing I would do is disconnect the linkage to the accelerator pump lever and see if it idles normally. You'll have to advance the throttle slowly to keep the engine from stalling since you don't have the pump anymore. This should narrow down your problem to either the pump or some other linkage or throttle return spring that isn't allowing the butterflys to close completely.

If the pump is the source of the problem just put the old stuff back in and see if that fixes it.

[kingderzelas]

5 minutes ago, drh said:

First thing I would do is disconnect the linkage to the accelerator pump lever and see if it idles normally. You'll have to advance the throttle slowly to keep the engine from stalling since you don't have the pump anymore. This should narrow down your problem to either the pump or some other linkage or throttle return spring that isn't allowing the butterflys to close completely.

If the pump is the source of the problem just put the old stuff back in and see if that fixes it.

Got it, ok that makes sense. Ill be getting my new spark plugs today or tomorrow and ill start messing with the linkages to see what's causing the high idle. Once its running right ill go ahead and change out the oil. 

[solorex]

22 hours ago, kingderzelas said:

From what Im understanding, I believe the high idle is the actual cause of why water is in my cylinders. I believe the high idle caused the motor to diesel, because when I checked later that day I saw my right (as you stand at the back facing front) exhaust flap completely sucked in. Only way it could have done that is if the motor dieseled and caused a strong enough vacuum for it to happen. Ill check the bushing.

 

Ah.  Didn't know that detail from your original post.  Yes if the engine rotated backwards for a second you could've sucked water in.  I'd still buy a couple riser gaskets and at least take the uppers off to make sure everything is OK and check the conditions of your manifolds.  This is easy to do.

[kingderzelas]

On 7/13/2022 at 12:46 PM, drh said:

First thing I would do is disconnect the linkage to the accelerator pump lever and see if it idles normally. You'll have to advance the throttle slowly to keep the engine from stalling since you don't have the pump anymore. This should narrow down your problem to either the pump or some other linkage or throttle return spring that isn't allowing the butterflys to close completely.

If the pump is the source of the problem just put the old stuff back in and see if that fixes it.

So I can confirm that the throttle return spring isn't allowing the butterfly's to close completely. I found a workaround solution where I can attach my own spring to loop in the linkage and anchor it to a point a little further back. I bought several different kinds to test out, but I'll use it like this until I can replace the linkage assembly.

I plan to siphon out the oil two times before taking it out on the lake again. Which leads to one of my original questions of what kind of oil should I be running? Is the highest viscosity royal purple/mobil 1 I can find at auto zone sufficient?

[justgary]

Most of us use Delo 15W-40 diesel oil.  It has an S rating as well as C rating.

Did you clean and rebuild the carb, or just change a few parts?  It sounds like maybe something is still funky with it.

I agree about checking your manifolds and risers.  They rust out and spill water into the cylinders.

[jayR]

until you work out the problem and make sure the engine just run the cheapest walmart oil...  I also recommend checking the risers and manifolds.