Mercruiser 5.0 damage..Hydrolock? Spun Rod Bearing??...Need some suggestions

[btwint]

Great forum and especially helpful for Boaters like my self. We have a 1999 Bryant with a 5.0 Mercruiser carb with about 650 hours.

I will try to explain the events leading up to our engine problems. Engine has been maintained through out its life by a reputable boat mechanic. Did oil change this season and current oil level is fine. Have used the boat almost every weekend this summer with no issues.

Today we put the boat in, engine started as usual with very little effort and was running great. No high temps and oil pressure was fine. We took off out of the no wake section and was still running great. Stayed around cruising speeds and was doing just fine. Went under a bridge and then took off again...still fine. As we picked up speed one of our passengers lost their hat. I circled back to grab the hat. As I pulled by it they were not able to reach it. Boat was in neutral and lake was not busy so I decided to hop in to grab the hat.

Good news is I saved the hat. Bad news is while I was swimming back I asked the wife to shut off the boat. She turned the key off but the engine still tried to keep running. (It has done this a couple times before over the last few years and I have always just turned the key back on to give it some fuel and then try shutting down again. It’s always done fine). Today however my wife just turned it off, engine tried to keep running and she didn’t know so left the key off. It eventually bogged down and shut off.

I climbed aboard, turned on the blower and turned the key. NOTHING! Almost like the motor was seized. I thought for a second that maybe it was in gear so I wiggled the shifter to ensure it was in neutral and tried it again. It turned over maybe a half a turn and sounded like it was straining pretty hard to turn over. At this point I popped open the hatch, looked for anything obvious, check oil level and for any leaks. Everything looked fine, nothing out of the ordinary. Turned it over again and it turned over but I heard a thump almost like a rod or something.

I then decided that I was done and feared I would cause more damage if I continued trying. We got a tow back to the ramp and I pulled her home.

Any idea what could have happened? I’ve read about hydro locking and how important it would be do get water out of cylinders if present. What would your first steps be other than getting it to a mechanic? I will Monday but am now scared if it does have water in cylinders and I let it sit it could be bad news. Thanks for you help.

 

[alldodge]

Good news is I saved the hat. Bad news is while I was swimming back I asked the wife to shut off the boat. She turned the key off but the engine still tried to keep running. (It has done this a couple times before over the last few years and I have always just turned the key back on to give it some fuel and then try shutting down again. It’s always done fine). Today however my wife just turned it off, engine tried to keep running and she didn’t know so left the key off. It eventually bogged down and shut off.

The motor hydrolocked and it happened because the dieseling was never fixed

When the motor runs on (dieseling) it runs backwards before it stalls and this sucks in water.

Remove the spark plugs and crank the motor over to get the water out now

 

[Scott Danforth]

Any idea what could have happened? I’ve read about hydro locking and how important it would be do get water out of cylinders if present. What would your first steps be other than getting it to a mechanic? I will Monday but am now scared if it does have water in cylinders and I let it sit it could be bad news. Thanks for you help.

pull plugs now

crank it over without plugs now

squirt a bit of ATF in the cylinders thru the spark plug holes after you get the water out

then turn it over and get the ATF out

then put in new plugs

hook up muffs and get the motor running today

then fix the dieseling issue.

 

[Rick Stephens]

↑↑↑↑↑ ... And change the oil and filter.

 

[btwint]

Thank you to everyone that responded and all the post about this. I completed the work above today and the engine is turning over smooth. It turns over great and fires up on the first turn.

I ran on muffs for a little bit to get it warm and noticed no water being expelled from the prop or exhaust. I didn't keep it running long and decided to try a large bucket and completely submerged the foot. Same results, no water circulation.

Where should I start? Impeller? T-Stat?

The drive is a Alpha One Gen II.

 

[Rick Stephens]

Sounds like impeller..... but dieseling isn't going to cause that. Wonder why....

Anyhow, if you want to know if any water coming from the impeller, pull the in line at the thermostat (the line coming in from the transom on the port side through the oil cooler) and with the water on to the muffs, fire up the motor. Should see good flow of water coming out in less than a minute. If not, pull the drive and go to draining, splitting and inspecting the water pump.

 

[Scott Danforth]

Never attempt to run in a bucket unless the bucket is big enough to float the boat

The whole drive needs to be submerged to prime the pump

Thats why you use muffs

Now pull your drive apart and replace the impeller that is now toast

 

[btwint]

Thanks Rick. I will pull the inlet hose tomorrow and give it a try.

If I dont get good flow then I would start at the water pump. Would I just order the full water pump repair kit?

What happens if I do have plenty of flow then re-connect and still not cycling water? Should I be looking at the thermostat next?

 

[btwint]

Never attempt to run in a bucket unless the bucket is big enough to float the boat

The whole drive needs to be submerged to prime the pump

Thats why you use muffs

Now pull your drive apart and replace the impeller that is now toast

Thats a big bucket.

I do get what you are saying and it wasnt just a bucket. I should have described it more as a tub or a bin. It is about 45 gallon tub and it was actually large enough to submerge the entire drive.

 

[Scott Danforth]

Thats a big bucket.

I do get what you are saying and it wasnt just a bucket. I should have described it more as a tub or a bin. It is about 45 gallon tub and it was actually large enough to submerge the entire drive.

you really arent listening

unless you stood the boat on end, you cant get the whole drive submerged in a bucket. maybe if you took a garbage can, cut out a u-shaped hole and duct tapped it to the hull, however it would probably come loose prior to you filling

the whole drive, all the way up to the top needs to be in water to get the water pump to prime, or you need to force water up the drive with a hose and use muffs. since muffs are easier..... use muffs and turn up the hose on full.

since you attempted to use a bucket, and since the boat is in the way to get the drive submerged, you toasted your impeller.

 

[alldodge]

Back to the cause
Dieseling is caused by the idle is set to high, running rich and or running hot. Idle should be 650 rpm

 

[Bt Doctur]

Below the Red line is your water pump and it cannot be submerged in a tub, the typical water level is the Blue line .The impeller moves water, dosent suck water
click to enlarge

 

[Lou C]

Plus when the impeller primes, all the air that is in it has to get expelled for it to move water. I always cringe when people try to run a boat engine with the drive in a bucket. Impellers cannot move air only water. Buckets work for small outboards where you can submerge the whole lower unit.....

 

[btwint]

Ive learned two things today.....

1. Dont run the I/O on large bins
2. Some of the members tag line under their name are EXTREMELY accurate

Seriously though, thank all of you for your help. Its odd that everything worked fine until the dieseling. I plan to check the inlet hose and see if I am getting water while on the muffs. I guess if the flow is good I will consider the impeller to be ok and then inspect or replace the thermostat.

All the while I will be trying to find out what is causing the dieseling in the first place.

Anyone see anything wrong with this approach? Is it possible to get flow from the inlet but still have an impeller issue?

On a side note...I have never thought about this but now I am curious. While out on the water how can you be sure the water is circulating properly, other than the boat running hot? I know outboards sometimes have a place where water is ejected letting you know there is circulation. Is there an easy way on an stern drive?

 

[Scott Danforth]

you already toasted the impeller. pull the drive and replace it. it only takes 10 seconds without water flow to melt the impeller, and at 20 seconds you melted the whole pump housing.

regarding the dieseling, verify your timing is correct, verify your not running rich (dirty carb). best way is to read the plugs

as far as water circulating properly - once you have the raw water impeller replaced. put muffs on outdrive, hook up hose and turn on full. water will spray out until you get the boat started. do not run over 1500 RPM as your hose cant supply enough water. your hose should be supplying a minimum of 15 gpm. (fill a 5 gallon bucket in under 20 seconds).

water will come out the idle relief ports and the prop.

 

[btwint]

you already toasted the impeller. pull the drive and replace it. it only takes 10 seconds without water flow to melt the impeller, and at 20 seconds you melted the whole pump housing.

regarding the dieseling, verify your timing is correct, verify your not running rich (dirty carb). best way is to read the plugs

as far as water circulating properly - once you have the raw water impeller replaced. put muffs on outdrive, hook up hose and turn on full. water will spray out until you get the boat started. do not run over 1500 RPM as your hose cant supply enough water. your hose should be supplying a minimum of 15 gpm. (fill a 5 gallon bucket in under 20 seconds).

water will come out the idle relief ports and the prop.

Thanks Scott. I appreciate the advice and quick responses. Will order the kit now and get the impeller replaced.

As far as reading the plugs...other than them being wet with the water that got sucked in they were all fairly burnt looking. I will clean the carb as well.

 

[alldodge]

On a side note...I have never thought about this but now I am curious. While out on the water how can you be sure the water is circulating properly, other than the boat running hot? I know outboards sometimes have a place where water is ejected letting you know there is circulation. Is there an easy way on an stern drive?

Install a 0-30 or 40 psi water pressure gauge, and place the sender in the block. I installed a mechanical gauge using a Tee fitting on the block drain to the Helm. Can keep an eye on it now.

Without a gauge just hope your over heat switch and alarm horn don't fail. Next to that set a schedule to replace with time

 

[btwint]

After a very busy week I finally had some time to pull the foot off and get the water pump kit installed.

Before I got to the replacement of the impeller I ran into something I have some questions about. When I separated the bottom end 3 things basically fell out. I’ve looked up and they appear to be water flappers for the exhaust but how in the world did they get blown into the drive? It appears to be only 3 so I guess the other is still connected?

Any ideas?

 

[alldodge]

They go into the drive thru the exhaust boot thru to the prop. The prop will not pass them so they start to block the exhaust and therefore reduce power to the motor.

Look in the Y-pipe and suggest replacing the flappers.

 

[Biggyniner]

Explains the water being sucked into the engine. Those flappers are there to prevent that