bad night on the water help!

C

chillywater

New Member
Jun 10, 2007
9
First off I have 03 240 bowrider 496 mercruiser with about 170hrs on it.


Last night went to a bar with some friends. We were riding back to the house and ran into some millfoil (sp?). Well I notice that my boat was running the same rpms but was slowing down then the engine got hot and sputtered and we had to shut her down. Pretty scary in the middle of a 4 mile wide river about halfway between both locations (30 min ride). We got it cranked and went really slow back the way we came. If you gave it gas it would choke it. When it shut down the engine was running hot but after that it ran about 170 degrees. Picked it up this morning expecting to find a bunch of weeds around the prop but instead found it around the water intake for the outdrive. What could be my problem and how do I make sure that it is cleaned out if it is clogged up. Engine cranks just fine and oil pressure and temp is ok.
 
I don't know what milfoil is? As far as something around the water intake, that is important. Clean out those holes thoroughly. I would highly recommend removing your sea pump and checking the housing and impeller. One or both are likely damaged from running dry at speed.

If you do take the pump off, check the end pieces that ride against the side of the impeller as well as the outer area the vanes sweep. The 496 pump leaves a lot to be desired. The ends tend to wear significanlty which will allow the pump to suck air and then fail. If the ends do have pronounced grooving, it needs to be addressed. A new pump is about $400. I know a place the makes a kit that can repair the pump as well as greatly improve its longevity for quite a bit less.
 
I don't know that there is a reason to treat milfoil differently than anything else that may block your water intake. For me, that means clean it of and go, watching the engine temp. I doubt that milfoil would damage your water pump.

I suspect you had more milfoil on the outdrive when it slowed you down than what you saw later. It may well have just drifted away when it was not being pulled through the water.

It is good to know where it is if you are in a river. Locally, a young man from Seattle was drowned by milfoil in the Columbia by Kennewick, WA. Several people were swimming in the river, and he got his legs caught in milfoil and panicked, could not get them free. This happened in the evening, they found him the next morning.
 
I hate that stuff. Whenever I leave my dock I have to stop once I get clear of it and rev the engine in reverse and forward a few times to clean it off.
 
My advice;

1) Go to Sears and buy an infared temperature gun. (I bought one two weeks ago for $80)

2) Take the boat out, warm it up, and at progressively increasing speeds. I would do this on the way to the bar :thumbsup: At each speed point, monitor your temperature gauge, and confirm temperatures using the IR gun. Check the top of the raw water pump housing. Monitor the points where the temperature sensors are located. Also check the riser, and exhaust elbow temps.

4) If all the temps look good. . .continue to the bar and buy a round! :smt038 . Also. . .write down all the temps, because you just established a temperature baseline for the engine.


If something is wrong, probably ALL the temps will look bad. Note that on my 1997 5.7LX, the temperature guage and temperature alarm are driven by DIFFERENT sensors. If your gauge is high and the alarm comes in. . .you ARE overheating.


If you are having a problem, the MOST LIKELY cuplprit will be the raw water pump. (unless this engine has a second impeller in the outdrive or on the engine ahead of the raw water pump -> in which case go after that!)
 
I'm with Dave,
I'm sure you were never dry to damage anything. The Milfoil just choked the flow. Now that you're clear it should run at temp.
Once reason why it sputtered was because of getting too hot. That is where I would take comsnark's advice and just double check temps.

Sounds like you caught it in time, but yes Milfoil can be a pain.
milfoil.jpg

Kimballs.JPG
 
The pump obviously went dry, or the motor would not have overheated. The impeller is made from neoprene which has very little resistance to heat, it relies on the water flowing through it to lubricate and cool it. Without water, failure is imminent, especially at cruising rpm's. Even if it is flowing water okay now, the impeller has likely been very comprimised and could fail at any time. I would check it.
 
took it in today....new impeller is what he said was probably wrong. They are going to check everything and give it a test run before they get her back to me. I really didn't need that $300 dollars :smt009
 
Ouch, $300 to replace a $25 part. And burning your own gas to "test it". That's as good a reason as any to learn to replace your own impeller. It's usually a pretty easy task.
 
The impeller change on a 496 is not bad unless you have poor access to the front of the engine. The pump housings on 496's are known for early failure, and they are expensive (about $400 list). If there is significant wear (there often is), it must be addressed.
 
Been there. Done that. Twice this season. Done as part of troubleshooting a thorny problem. Yes, it is a 2-3 hours of mechanic time (including test) to replace the impeller. Yes, it is a $25-$50 part.

Is the boat still overheating? Or is the mechanic saying to replace it merely on your description which you gave here? I (unfortunately) have overheated a few times this season. Each time, the temp went up, the alarm came in -> and I shut down the engine. Never let it get to the point of "sputtering" (my engines are carbed, not fuel injected).

What does your engine run normally? Mine have 160F thermostats, and the gauges run 170F. The other options is a 145F thermostat, in which case your engines will run 150F or so ALL THE TIME.

From what you say, after you shut down (finally) and restarted. . .then you say you ran 170F? Could it be you were back to normal?

BTW: NEVER run your engine if it is overheated. Don't let it run if it is over 190F. (same applies to your car. Antifreeze will boil a bit hotter than normal seawater -> don't run it over 200F!). If it doesn't cool down when run at idle. . .you need to figure out what is wrong! When I overheat, the first thing I check is for clogged engine intakes. Then I poke into the engine compartment to see if "something stupid" has happened. (twice I have had Raw water pumps fail, and the engine belt was on the floor)

I understand the temptation to run a dead engine. Afterall. . .you would be STRANDED without it eh? But DON'T DO IT! I guess this is why I like twin engines. You get TWICE the headaches, but it is really rare to be totally stranded.

And if the engine is new. . .not such a bad idea to have the mechanic check it out anyway.
 
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