shot impeller?...plastic bag overheating

New to forum!...about 5 months ago my salt water use engine was serviced w/o particular reason, it was just time (350 MAG MPI/Bravo III, 2004 SeaRay 260 w 220hours ), service included new impeller kit and thermostat. After uneventful 5 trips/15 hours or so I took it out and had the smartcraft engine overheating alarm after about 10 minutes of going in idle/minimum speed (<1500) rpm. Limped back to the dock at idle, temp never went higher than 220. Brother in law at dockside reports smoke coming from back of boat...

So engine ran at idle with overheating alarm on for about 10 minutes.

After raising the boat (lives on floating lift) a plastic bag floated from below the boat and washed on one of the pontoons. I didn’t pay any attention at the moment so I just went home thinking about having to call a mechanich after the holidays.

NEVER had an engine overheating issue before. Last week I flushed the cooling system as I normally do (muffler ears and hose with salt off). I run it on neutral at about 1200, wait for engine to reach temp then allow the salt off solution to circulate for about 5-10 min then shut engine off, then remove hose. Temp has always stayed nicely at 159F as usual.

Questions:

1. IF THE ISSUE WAS THE PLASTIC BAG COVERING THE WATER INTAKE AT THE DRIVE: is the recently changed impeller potentially damaged already?.
2. Any other parts that may need to be checked as consequence of ~10 minutes of idling the overheated engine?
3. What would be the potential source of smoke?...just overheated exhaust ?... rubber from impeller or a gasket being burnt?

Ayuh,...... A plastic bag, Stops the water flow, so yes, the impeller is probably junk, 'n possibly the pump housin',...

When there's no water flow, All of the rubber parts in the exhaust get burnt up, couplers, shutters, All is suspect,....

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Pluterday said:

New to forum!...about 5 months ago my salt water use engine was serviced w/o particular reason, it was just time (350 MAG MPI/Bravo III, 2004 SeaRay 260 w 220hours ), service included new impeller kit and thermostat. After uneventful 5 trips/15 hours or so I took it out and had the smartcraft engine overheating alarm after about 10 minutes of going in idle/minimum speed (<1500) rpm. Limped back to the dock at idle, temp never went higher than 220. Brother in law at dockside reports smoke coming from back of boat...
So engine ran at idle with overheating alarm on for about 10 minutes.
220 degrees is dangerously high.
The smoke may be an indication of over-heated and blistering rubber exhaust components.
10 minutes at high temperature run-time is dangerous.


After raising the boat (lives on floating lift) a plastic bag floated from below the boat and washed on one of the pontoons. I didn’t pay any attention at the moment so I just went home thinking about having to call a mechanic after the holidays.

NEVER had an engine overheating issue before. Last week I flushed the cooling system as I normally do (muffler ears and hose with salt off). I run it on neutral at about 1200, wait for engine to reach temp then allow the salt off solution to circulate for about 5-10 min then shut engine off, then remove hose. Temp has always stayed nicely at 159F as usual.
In order to avoid salt water Crystallization, Raw Water Cooled engines operating in Salt Water should not exceed temps of 145*.

Questions:

1. IF THE ISSUE WAS THE PLASTIC BAG COVERING THE WATER INTAKE AT THE DRIVE: is the recently changed impeller potentially damaged already?.
Yes, not only damaged, but as Bill said, it may have also damaged the seawater pump's impeller housing.


2. Any other parts that may need to be checked as consequence of ~10 minutes of idling the overheated engine?
Yes... the 10 minute run-time and the smoke suggests that you should look at/replace ALL of your rubber exhaust components.

3. What would be the potential source of smoke?...just overheated exhaust ?... rubber from impeller or a gasket being burnt?
yes, yes and yes.
Also, it is highly likely that some impeller vane fragments have become dislodged and are now stuck within the seawater path.
These MUST be found and removed!


Good luck with this!

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The pump believe it or not is probably fine. The housing is Bronze and Merc says it can run dry for multiple minutes dry with no damage. Your pump was not completely dry just restricted.

If you have a Smartcraft gauge, thumb through it until you find the water pressure screen. What water pressure reading do you have at idle and at 3000rpm?

The smoke is from lack of water in the exhaust, Can be the rubbers burned or burned paint.

Next time you get an over heat, check the water pressure, if zero,(should set an alarm also) shift the drive into reverse to clear it. If pressure comes back and temps drop, you're ok. If not...SHUT THE ENGINE DOWN!

Post the serial number to see what pump you have.

Pluterday: I just posted after you about a 262 Monterey with 383 Mag Stroker 350 hp MPI.
Your boat 260 searay and mine are about same weight and similar engine as yours.
Wondering what your hot idle oil pressure is and what Bravo111 prop you are running.
My engine runs about 4000 rpm at 30 mph. About 5000 rpm at 40 mph. WOT 5200 rpm
Wondering if I am lugging my engine causing fuel dilution 11% in both new engines.
I have a oil tempature guage in my oil pan and it reads 220 F when on plane 30 mph. Water temp never changes from 160 F.
I can not figure out what is causing fuel in my oil on these MPI engines.
Suspect controls are adding too much fuel for some reason.
Thanks JackA

Pluterday said:

Thanks for the replies guys. Chris, the engine S/N is 0M669025

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It has a Bronze pump.

JackA said:

Pluterday: I just posted after you about a 262 Monterey with 383 Mag Stroker 350 hp MPI.
Your boat 260 searay and mine are about same weight and similar engine as yours.
Wondering what your hot idle oil pressure is and what Bravo111 prop you are running.
My engine runs about 4000 rpm at 30 mph. About 5000 rpm at 40 mph. WOT 5200 rpm
Wondering if I am lugging my engine causing fuel dilution 11% in both new engines.
I have a oil tempature guage in my oil pan and it reads 220 F when on plane 30 mph. Water temp never changes from 160 F.
I can not figure out what is causing fuel in my oil on these MPI engines.
Suspect controls are adding too much fuel for some reason.
Thanks JackA

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Jack, interesting!. Is the oil temp gauge an aftermarket addition or smartcraft is supposed to report it somewhere?...I’m only familiar with the 159F temp reading I assume is water temp

Engine oil tempature is from a in dash aftermarket Oil Tempature Guage.. The sending unit is installed in oil pan drain plug hole.
Before I had this guage I thought my low hot idle oil pressure was because oil was getting too hot and thinning out.
Because of this guage I now know oil is thin because of fuel in the oil from oil Analysis not overheating.
I was thinking I needed to add an oil cooler like other versions of this engine.
Still why both brand new engines are get fuel in oil is a mystery to me?

JackA said:

Engine oil tempature is from a in dash aftermarket Oil Tempature Guage.. The sending unit is installed in oil pan drain plug hole.
Before I had this guage I thought my low hot idle oil pressure was because oil was getting too hot and thinning out.
Because of this guage I now know oil is thin because of fuel in the oil from oil Analysis not overheating.
I was thinking I needed to add an oil cooler like other versions of this engine.
Still why both brand new engines are get fuel in oil is a mystery to me?

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The first engine was a complete drop in....when that failed did they send another complete drop in under warranty or did they send a long block?

2nd engine was a complete drop in. Same as first engine.
First complete engine was sent back to Mercruiser.
Have yet to hear if they disassembled or tested for cause of rod bearing wear.

Docksidemarineservices said:

It has a Bronze pump.

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Went back today to try the engine, it tries to turn, you can see the belt trying to turn for like half an inch but feels like there is something mechanically preventing it from moving and it stops. A mechanic will take a look tomorrow. Any ideas where to look firat are welcome (burnt impeller or exhaust muffler will prevent engine from turning?..). Engine ran fine for the <10 min I had it between 200-220 (fw and reverse).

Battery reads full charge (never had issues with batteries), no obviously burnt cables...

Pluterday said:

Went back today to try the engine, it tries to turn, you can see the belt trying to turn for like half an inch but feels like there is something mechanically preventing it from moving and it stops. A mechanic will take a look tomorrow. Any ideas where to look firat are welcome (burnt impeller or exhaust muffler will prevent engine from turning?..). Engine ran fine for the <10 min I had it between 200-220 (fw and reverse).

Battery reads full charge (never had issues with batteries), no obviously burnt cables...

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Water in the cylinders.

To close the loop, long story short, boat ended up at my mechanic's shop, diagnostic is water in cylinders (Chris was right), shot impeller, etc. Filed an insurance claim and adjuster recommended a new engine block. Shop is installing a Mercury remanufactured long block (see below link), plus new impeller, raisers, manifolds, plugs, gaskets, thermostat, etc and fixing a couple other things. Long story short, I'm very lucky as I'm practically getting a new engine for a fraction of the price (most of it insurance deductible), but learned my lesson: no matter what, not even for a few seconds, run an overheated engine.

https://www.mercurymarine.com/en/us...ndrive/remanufacturing/pro-series-longblocks/