Engine won't turn over

Flytrade

Flytrade

Active Member
Feb 20, 2018
302
Bradenton, FL
Boat Info
2006 320 Sundancer
Engines
Twin 6.2L Mercruiser
I have a Mag 350 engine with Bravo 3 outdrive with 650 hours, and which has always performed perfectly. However, after an afternoon of cruising at 3,800 rpm and idling to a dock, I tried to start the engine 5 minutes later and it won't turn over.
When I try to start the engine, the starter appears to engage the flywheel and turn it just a little until it comes to an abrupt stop with a metallic sound. The whole process takes less than a second.
All the gauges are in the normal range - temp and oil pressure. I also checked the oil, and it is full with the normal color indicating there is no water, etc. in the oil.
Any thoughts on what might have happened in that 5 minutes to this perfectly normal operating engine?
 
Called hydrolock, STOP CRANKING THE MOTOR
pull the sparkplugs then crank the motor to clear the cylinders
 
Yup it's hydro locked! Not good and stop turning the key. BD is right pull all plugs and then turn it over and over several times to pump the water out. Spray some lube in the spark plug holes and turn the engine over a few times. Put the plugs back and fire it up. Listen very careully for any unusual sounds. If normal then that's a good day. If sounds turn it off and get a mechanic on it. Damage has been done.

Now you must figure out why water got there in the first place. The two most common ways...
You slowed the boat down way to fast and the back pressure was to low so water traveled backward down the exhaust to the engine. Required fix. Don' slow down fast and get higher risers.

Or the manifold failed and it' flooding the engine. Required fix. New manifolds ASAP.

Just pray you hear no ticks, clanks, clunks or bangs when you start it....

Good Luck!
 
However, after an afternoon of cruising at 3,800 rpm and idling to a dock, I tried to start the engine 5 minutes later and it won't turn over.

That says it was running or idling at least so my guess is a failed elbow or manifold depending on the type of exaust system.
If standard manifolds , remove the bottom hoses and run the engine for very short periods to dry the cylinders, about 30 secondseach time checking the rubber exaust components
If dry joint type remove the serpentine belt and run motor for 30 second periods to dry the cylinders again checking the rubber components
 
Thank you for all the good advise, and everything you bring out is very logical. However, could you explain why the engine ran so well at cruise, and at idle, and then hydro-locked 5 minutes later? If the problem is water in the cylinders, would it not get there while I'm running, and I would know that because the engine should not perform correctly with water in the cylinders along with the gas? Also, one thing I did not mention is that I also just refueled the boat with 50+ gallons of gas. Could the water come from water in the fuel? Thanks again for your thoughts.
 
Flytrade said:
Thank you for all the good advise, and everything you bring out is very logical. However, could you explain why the engine ran so well at cruise, and at idle, and then hydro-locked 5 minutes later? If the problem is water in the cylinders, would it not get there while I'm running, and I would know that because the engine should not perform correctly with water in the cylinders along with the gas? Also, one thing I did not mention is that I also just refueled the boat with 50+ gallons of gas. Could the water come from water in the fuel? Thanks again for your thoughts.
Click to expand...

I think it is fair to say we don't know exactly what is wrong with your engine. Regardless of what we think it may be....you have to pull the plugs and have someone crank the engine. It either spins and spits water out of the spark plug holes or it doesn't spin at all. It may not have anything to do with an action that you took. Mechanical failures happen. Taking on fuel had nothing to do with it.

Report back what you find. CSR is a great resource for fixing things!
 
My assumption is there is a small leak in one of the manifolds and while running hot the water is moving out the exhaust. Once it was off the water now standing in the bad manifold drips down one of the cylinders. It only takes a couple of teaspoon to lock a motor. The failure probably happened during your last run. Thin casting or just old and gave out.

I had the exact same thing happen on an older boat I had 10 years ago. All Good, then on the next start. Locked up. Pulled plugs and there was water. Saltwater. Filled with lube and had mechnic down next day. That saved the engine. If i had waited even 48 hours with salt in the engine it would have been toast. Don' wait even with fresh...!
 
I have a mechanic coming by this morning. I'll let you know what he finds. Thanks again.
 
did yuu happen to notice a miss that went away or a hard crank that sounded like a weak battery , thats the beginning of a hydrolock
 
The mechanic pulled the plugs and found water in the aft/starboard two cylinders. The boat has been towed to his marina for repairs. I'll keep you updated as to what he finds.
 
Bt Doctur said:
did yuu happen to notice a miss that went away or a hard crank that sounded like a weak battery , thats the beginning of a hydrolock
Click to expand...
No I did not. The engine started and performed as usual, at cruise and at idle. Then, after being shut down for about 5 minutes, this happened.
 
most likely the manifold has a crack in it or the elbow
You dont list a location but if its salty you have about 24-36 hours to get it running to save it. Also have a oil change done BEFORE the motor is started just incase water got past the rings into the oil. If you dont the first start may show up as water mixed with the oil for a false indication of more trouble.
 
I just got a call from my mechanic, and it does not look good. I was hoping it would be a gasket, but he said it was not the manifold, riser or elbow. He thinks it's either a head gasket, the head itself or a cracked block. He said the only way to know for sure is to pull the engine and put it on a test stand. I asked if the head could be pulled without removing the engine, but he said, for several reasons, it would be better, faster, less expensive to pull the engine and give it a full inspection. I gave him the go-ahead and he said he should know more by next week. It's still amazing to me how the engine could be running perfectly, and 5 minutes later be in this fix.
 
Sounds like BS. Easier to pressure test the water side while everything is still assembled. Could be a head gasket but wants to pull the motor ???? The motor mounts in your boat are the test stand
 
That doesn't sound right to me. We just pulled the heads on a 454 while in the boat. We did end up pulling the engine but only after a pressure test
 
If I understand the OP, cylinders 6 & 8 are the problem. Blown head gaskets (cracked blocks and heads) usually leak coolant (I believe the OP's boat has closed cooling) into the combustion chamber. Any good mechanic would be able to tell the difference between a raw water failure and a closed cooling failure without doing a lot of diagnostic.

The possibilities that his mechanic suggests fit a closed cooling failure. Let's say that he is right. Pulling the engine seems a bit extreme at this point but some mechanics do it if they believe a new/rebuilt engine is going to be required.

I have worked on engines for a long time and raw water wins 9 out of 10 times over closed cooling engine failures (except with race boats where the odds change to 50/50). So.....if he thinks it is the 1 out of 10 version.....I will be very curious what he actually finds.
 
Sorry to hear....hope their is a light of good news somewhere in This mess
 
This is a raw water cooled, dry joint manifold, 650 hour motor, correct?

Are these the original manifolds and risers?
Is it salt or fresh water?

After oiling down the cylinders, the mechanic should have removed the risers and manifolds, about 2 hours labor. Removing them makes it easier to remove the motor anyway.

Any rust stains in the manifolds?
Any rust on the tubular gasket?(thats the riser gasket with a raised lip to catch condensation in the exhaust)

With those parts removed, he should be able to block off the hoses and pressure test the cooling system right there in the boat.

I realize you've already approved the work to remove the motor.
 
First of all, all your comments are great. I'm a retired pilot, so this engine problem is an area that I am not familiar with.

And yes - it is raw water cooled with 655 hours. I bought the boat about 4 months ago with 625 hours, and it has been running perfect. I'm not sure the process of pressure testing the cooling system with the engine in the boat, but I will talk to him about it tomorrow.

However, here is a little background on this marina, and this mechanic in particular. This marina was recommended by a neighbor who has been using them for a couple of years, and speaks very highly of them. I also had a leak in my trim tab system, and the mechanic added oil to see if that would be a simple fix, and only charged me for the oil. Of course I gave him a nice tip for his time.

I also had a battery charging problem, and he found a lose wire on the alternator. He could have charged me for a new alternator, etc. but did not. Both these items give me a good feeling about their honesty and doing business with them.

Although I can suggest the pressure test to him, I feel I am also in the position of trusting him or towing the boat to someone else, but I would not know who else to bring it to. Then I would be dealing with an unknown marina, mechanic, etc. I'll let you know how this plays out.
 
You must log in or register to reply here.

Forum statistics

Threads
113,118
Messages
1,426,544
Members
61,035
Latest member
Lukerney
Back
Top