Mercruiser 3.0 overheated, Is my motor shot?

[Hatch19]

Hey Guys. Took the boat out. Had it idling for maybe 10 mins and took off on a plane for about 90 seconds. Motor started loosing power, noticed smoke from the engine bay and shut it off. Smoke was coming from the rubber that connects the exhaust riser to the pipe going to the transom.

Got towed back to the dock and when trailered found the water Intake hose came disconnected from the gimble. Haven’t tried to start the motor since.

Any suggestions, tips, order of operations (aside from fixing the water hose) on what to check before I attempt to fire it back up or is my motor shot?

 

[cyclops222]

10 minutes of idling will cook some motors. Not enough cooling water being pumped. Some cars have the same problem.

 

[racerone]

Is there not a gauge or overheat warning horn?-----These units need a new impeller every 5 years.----Compression test needs to be done before restart.

 

[Hatch19]

Is there not a gauge or overheat warning horn?-----These units need a new impeller every 5 years.----Compression test needs to be done before restart.

No warning horn and I just replaced the impeller 2 months ago. It’s ran fine each time out until now… when the water intake hose disconnected… as stated

 

[Hatch19]

Is there not a gauge or overheat warning horn?-----These units need a new impeller every 5 years.----Compression test needs to be done

 

[airshot]

These motors often warp the head when they overheat. It might pay to pull the head and see if motor turns over. You can check for cylinder scoring and check for warped head and be sure deck is flat. Better to be safe than sorry....

 

[nola mike]

I'd do a compression test, make sure it turns over easily, let er rip and see what happens. Can't imagine removing the head just because. Your rubber boots and flappers are toast, and you will need to find out where the pieces ended up. And even without the compression test you'll know pretty soon whether you have a problem.

 

[Hatch19]

I'd do a compression test, make sure it turns over easily, let er rip and see what happens. Can't imagine removing the head just because. Your rubber boots and flappers are toast, and you will need to find out where the pieces ended up. And even without the compression test you'll know pretty soon whether you have a problem.

I did bump the key when I got
Home, fuel off, and it turns over easy, so it’s not seized. I have already written the flapper and boots as toast considering I can pull the pieces out the exhaust bellow.

 

[Mc Tool]

Sounds like you got on it quickly , specially if the smoke was from the rubber exhaust bits. You dont really want to be pulling big bits off . Maybe the heads took a hit but if you pull them and see the bore aint so flash you'll wanna do them........can of worms
Make sure the oil is ok , fix your cooling system and kick her in the guts and see what happens . Got nothing to loose. If oil pressure is ok and it doesnt overheat, runs ok ,no nasty noises .....go boating

 

[Kola16]

It is common that the exhaust manifold(s) crack when marine engines are overheated. When that happens, it leaves a direct path for water to enter into the cylinders through the exhaust, hydrolocking the engine. A pressure test of the exhaust manifold and riser is the right thing to do. If not a pressure test, check to see if the spark plugs are wet after a couple minutes of running. Then 10 minutes after running if they were dry after the first couple minutes.

 

[cyclops222]

That hose coming off was the overheat problem.

 

[Scott Danforth]

Besides the compression test, to check motor health, all the rubber bits in the exhaust needs replacement.

You burned the flapper and the rubber couplings when the exhaust went from 220 with water to 1000 without water

I would also pull the lower and see how bad you toasted the raw water pump in the heat

 

[cyclops222]

Any plastic / rubber parts in the lower unit ? Ruined

 

[airshot]

With all the other stuff that needs taken apart to replace the rubber pieces and inspection, pulling the head would add less than an hour to your labor time. I am one of those " better to be safe than sorry" type guys I guess.

 

[cyclops222]

Add in valve O rings if cooked.

 

[ROY WILLIAMS]

It is common that the exhaust manifold(s) crack when marine engines are overheated. When that happens, it leaves a direct path for water to enter into the cylinders through the exhaust, hydrolocking the engine. A pressure test of the exhaust manifold and riser is the right thing to do. If not a pressure test, check to see if the spark plugs are wet after a couple minutes of running. Then 10 minutes after running if they were dry after the first couple minutes.

1978 Wellcraft Suncruiser 20FT. ENGINE 470. 170HP.COOLANT DISTILLED WATER 50%-ANTIFREEZE 50%.
1978-2025!
OUTDRIVE WATER - need OLD DESTROY impeller.

 

[Hatch19]

Checked a couple things this morning. Oil is still full and clean. No external oil leaks I can find. Quick Look at the exhaust manifold exterior doesn’t revel any cracks. Will start with compression test before I get to far into it. I’ll report back with numbers later. Thanks for everyone’s input!

 

[ScottinAZ]

Checked a couple things this morning. Oil is still full and clean. No external oil leaks I can find. Quick Look at the exhaust manifold exterior doesn’t revel any cracks. Will start with compression test before I get to far into it. I’ll report back with numbers later. Thanks for everyone’s input!

its not the manifold EXTERIOR that is the problem. The inner wall between the exhaust passages and the water jacket is where the issues will be... the exterior of the manifold is between air and water, and wont typically get that hot regardless. If its cracked internally, you WILL get water in the engine where you dont want it......

I had an issue with a worn out manifold leaking water on the hose back into the engine, and nearly hydrolocked it.... not a fun time... a cracked manifold would do the same, let water get where it doesnt belong

 

[nola mike]

I would also pull the lower and see how bad you toasted the raw water pump in the heat

His overheat occurred after the transom

 

[nola mike]

Any plastic / rubber parts in the lower unit ? Ruined

No