350 mag overheated to the point of alarms

[reference123]

We were heading in after boating at around 4700 rpm's when my 350 mag jumped to 180 degrees, the alarms went off and the engine shut down. At the time I couldnt find anything that was the cause.

We were almost at the marina so we let is sit and cool then limped in. After getting home and letting the engine cool down I was able to find a water line that had disconnected (bottom side of the engine so there was no way to find it while the engine was hot).

Oil level looks good and the oil is looks new. There was smoke in the engine compartment when it overheated but it looked like it was coming from oil that had spilled during the last oil change.

Where do I need to start in checking potential damage before heading back out. I suspect I will need to replace the water pump and impeller but beyond that, is there anything I should look for or any other likely damage?

Thanks

 

[Don S]

Re: 350 mag overheated to the point of alarms

I suspect I will need to replace the water pump and impeller but beyond that, is there anything I should look for or any other likely damage?

The exhaust hoses from the risers to the Y pipe would be one thing to check. With no water due to a bad impeller, you would burn up the hoses.

And why do you have oil in the bilge from an oil change. Clean it up before your bilge pump comes on and polutes the water you are boating in.

 

[reference123]

Re: 350 mag overheated to the point of alarms

Don,

Thanks for the response. It wasnt me that changed the oil and I didnt know there was any oil in there until this happened. The smoke just smelled of oil and was coming from underneath so I guess I am hoping it relates to some on the outside of the block versus on the inside just from the hope the engine isnt shot. I would never knowingly allow oil to leak into any of the lakes we use.

I will check the exhaust lines though.

 

[newport dave]

Re: 350 mag overheated to the point of alarms

You may want to check the exhaust shutters as well. They can burn and fall down into the Y pipe.

 

[reference123]

Re: 350 mag overheated to the point of alarms

I put it on the muffs today for about 60 seconds. The water pump is still working as water starting pumping out the bellows on the sides of the drive. Oil pressure was normal and the oil looked clean before and after running the engine.

No water was coming out the Bravo III drive though and water started to seep out the plastic nuts right in front of the risers.

I am guessing this means my exhaust hoses, flaps, etc melted and are blocking the exhaust system. What chance is there water would have gotten in the cylinders with the blockage?

I assume I should still replace the impeller. Should I do the water pump as well just as a precaution? I noticed my heat guage goes to 250 but it never registered over 180.

How likely is it I damaged a head gasket?

 

[reference123]

Re: 350 mag overheated to the point of alarms

Thanks for those that replied.

Mechanic pulled the drive yesterday and inspected exhaust system. Gotta give credit to Merc for their design as there was no damage. Engine shutoff as designed.

Replaced the impeller just as a precaution but everything else looked great.