Engine failure?

[MThershey]

Just bought a Sylvan with a 4.3 Mercruiser. I was having trouble with fuel cutting out, but tracked that down. So, I took it out to test it and do some fishing. The boat ran great across the lake. Good oil pressure and stayed cool. So, we stopped and idled around to see if it would maintain a trolling speed. The engine started to get hot (220 on the gauge). I put it in neutral and idled a bit, then turned it off. I noticed some smoke when it turned off from the exhaust. When I went to restart the motor, the starter kicked for a moment followed by a loud clunk. The motor won't turn over. When I try it, just the loud clunk. Oil on the dipstick is good, no oil outside the engine. Battery is strong. I have some automotive knowledge, but not much with boats. I will try to turn the motor manually today. I can't imagine what would break internally when the starter didn't even turn the motor over and the motor was running when it was turned off.

 

[Bt Doctur]

220 is waY beyond a safe temp so guessing you blew the head gaskets and filled up a cylinder or 2 or 3 with wAter. PULL THE SPARK PLUGS.

 

[matt167]

220 won't cook a 4.3. they actually run around 200 212 In a truck. But in a boat that is smoking hot

 

[tank1949]

Just bought a Sylvan with a 4.3 Mercruiser. I was having trouble with fuel cutting out, but tracked that down. So, I took it out to test it and do some fishing. The boat ran great across the lake. Good oil pressure and stayed cool. So, we stopped and idled around to see if it would maintain a trolling speed. The engine started to get hot (220 on the gauge). I put it in neutral and idled a bit, then turned it off. I noticed some smoke when it turned off from the exhaust. When I went to restart the motor, the starter kicked for a moment followed by a loud clunk. The motor won't turn over. When I try it, just the loud clunk. Oil on the dipstick is good, no oil outside the engine. Battery is strong. I have some automotive knowledge, but not much with boats. I will try to turn the motor manually today. I can't imagine what would break internally when the starter didn't even turn the motor over and the motor was running when it was turned off.

BT is correct. Too hot. Sounds like a fresh water boat. How old? I suspect old or worn out impeller and maybe clogged risers or you sucked a plastic bag around water pickup. I did that once and temp went through the roof! I now have audio alarms in addition to gauges . Pull plugs and pray no water. Do compression tests on all cylinders, if it were me. You cannot compress fluids like lake water. Water over damn now, but in future, I have learned to be religious concerning maintenance and testing everything before first season's outing. One "aw-sh---" will wipe out 100 "at-a-boys."

 

[MThershey]

The boat is old, 1988. The motor is 1998 or newer from the serial number. We were in clean fresh water each of the three times time I had it out. The motor was stumbling and bogging down the first 2 trips. That was a simple fix. The hose clamp on the fuel line into the carb was very loose, so it was sucking air. The boat ran cool across the lake, but got hot when we were going very slow for less than 10 minutes.

 

[racerone]

Check the gear oil in the outdrive.

 

[MThershey]

How would that keep it from turning over in neutral?

 

[racerone]

First boat for you ?----Gears turn even in neutral.------A very simple inspection for you !!

 

[Bt Doctur]

iF THE ENGINE MADE A CLUNK, PULL THE SPARKPLUGS.

 

[Rick Stephens]

When the starter goes clunk, you probably have a cylinder full of water. Pull the plugs. (echo!)

 

[Bt Doctur]

Or you can keep trying and replace the starter too from a blown bendix drive gear

 

[wshekar]

Or you can keep trying and replace the starter too from a blown bendix drive gear

I might be more worried about bending a push rod or damaging a valve.

 

[nola mike]

Dunno if this has been suggested, but pull the plugs.

 

[tank1949]

When the starter goes clunk, you probably have a cylinder full of water. Pull the plugs. (echo!)

I'VE Been there!

 

[Lou C]

Yes pull the plugs, and being that the engine is a '98 does it have the one piece Mercruiser V6 exhaust manifolds? If so one may have failed and let water in a cylinder. Even with conventional exhaust, eventually they can rust through and put water in a cyl. Get the water out, or else you'll be replacing the engine. After that, inspect the entire exhaust system including the flappers at the top of the Y pipe. Check for water in the motor oil, look under the oil fill cap, it will show up there first, even sooner than on the dipstick. It will look like mayo.....
Here's a pic of mine from repairing the blown head gaskets (also from an overheat but the did not blow till 3 seasons later) and I wound up replacing the cyl heads with reman units.

 

[MThershey]

I pulled the plugs. There was what appeared to be a little water on each spark plug, but not enough to drain. I pulled the drain plugs. The motor turns freely. There is no milky appearance under the oil fill cap, but it did look like very small water droplets. The dipstick looks normal.

 

[Lou C]

OK and what exhaust does yours have? Merc 2 piece or 1 piece? I'd be looking at that as a possible source of water in the cyls. Make sure the flappers are in place at the top of the Y pipe.
Mercruiser 4.3L V6 Exhaust Manifolds | PerfProTech.com
read up on it here. The one piece units were prone to leaks due to difficulties in casting them with adequate wall thickness. If you have these you want to get rid of them, even if you have the 2 piece style you need to check them for leaks.
get the engine up and running ASAP to heat the oil enough to boil out the moisture....

 

[Rick Stephens]

Seeing as how pulling the plugs freed up the motor to turn - if there was water hydrolocking the motor, that water passed by the rings and is in the pan. It wil not have mixed, so you won't see it on the dipstick. Time to change the oil and count your blessings.

 

[MThershey]

Looks like a 2 piece?

 

[wshekar]

Yes. Those are 2-piece and after market. I have heard the GLM is the lowest quality after market version. Some like it cause it is also the cheapest.

You probably have a decent amount of water in the pan or still in the cylinders. Turn over the engine with the plugs out and see how much comes out each hole.