Overheating or just the circumstances of the moment...

[ChuckW]

So while on my last cruise I had a new twist to overheating I haven't seen before.

First some background...

My risers and manifolds are original. I have about 675 hrs on the engine. Two seasons ago I had them removed and inspected and was told they look great. Time for another look for sure.

Its a 496 with a closed cooling system.

Situation..

While running at cruise speed the engine temp was normal. It runs about 150-160 degrees. I had to come to an abrupt stop and shutdown the engine. While engine was off the temp shot up to 185+ degrees. So when I went to start back up the smartcraft alarm went off. I started the engine and let it idle for a minute or two and watched the engine temp come back down. All fluids are at normal ranges and stayed there.

This happened three times to me over the course of a 160 mile cruise through the keys. I have never seen this on this boat.

So does this make sense...is it a normal behavior or should I be looking at debugging this?

It makes sense that since I didn't give the engine some cool down time it would do this...but it is the first time I've experienced it even though I've done this before...

Thanks.

Chuck

 

[Xplicitlnck]

I noticed the same thing happening on mine and asked the same question on this forum. I got as followed. Its completly normal for a temp rise after shutting down as your circulating pump isn't circulation as much water and will cool slower. (Heat soak) I tbink they called it.as long as the temp comes down rather quickly you will be fine. Another response I got was that may be the first sign of bad thermostate or riser and manifolds or both. So I changed thermostate and riser and manifolds are an upcoming spring time project.
Hope that helps

 

[JimG]

So while on my last cruise I had a new twist to overheating I haven't seen before.

First some background...

My risers and manifolds are original. I have about 675 hrs on the engine. Two seasons ago I had them removed and inspected and was told they look great. Time for another look for sure.

Its a 496 with a closed cooling system.

Situation..

While running at cruise speed the engine temp was normal. It runs about 150-160 degrees. I had to come to an abrupt stop and shutdown the engine. While engine was off the temp shot up to 185+ degrees. So when I went to start back up the smartcraft alarm went off. I started the engine and let it idle for a minute or two and watched the engine temp come back down. All fluids are at normal ranges and stayed there.

This happened three times to me over the course of a 160 mile cruise through the keys. I have never seen this on this boat.

So does this make sense...is it a normal behavior or should I be looking at debugging this?

It makes sense that since I didn't give the engine some cool down time it would do this...but it is the first time I've experienced it even though I've done this before...

Thanks.

Chuck

So, why did you have to shutdown abruptly?

I know the waters in the Keys are skinny... don't know how long you have been running around there, but I would think sucking up the sand would cause premature failure of your impeller.

 

[skolbe]

I would replace your thermostat. I had a similar issue when I had a bad thermostat. If original buy the plastic housing at the same time.

 

[ardeprint]

An abrupt stop to to a hot and running engine WILL cause the water in the engine to heat up due to lack of circulation. The water that normally cools the metal will now be heated by the metal. This reaction will be picked up by the temp sensors as an overheat.

It is not good for the longevity of your engine to stop it abruptly. Let it settle at idle for a few seconds. If you must shut down abruptly let the engine cool down before restart. This will give you some leeway if you are having a cooling system failure. Remember at around 200 degrees water boils and engine blocks or heads crack.

 

[ChuckW]

Thanks for all the input. Yes, as I mentioned, it makes sense that things would heat up a bit by not giving it cool down time, but to this degree I had not seen before. It's time for service and inspection of risers, but I'll have the t-stat looked at too.

As far as the reason for stopping...well two times were due to build up of seagrass on the outdrive which caused excessive vibration while under way. Had to get in the water and clear it off the drive. Second was due to snagging one of those million pot buoys. Fortunately no damage done to drive, but it is like a mine field out there...

Thanks again!

 

[scoflaw]

.well two times were due to build up of seagrass on the outdrive


I think this is reason for your problem. Restricted water flow to motor

 

[ardeprint]

.well two times were due to build up of seagrass on the outdrive


I think this is reason for your problem. Restricted water flow to motor

I would agree that perhaps this could be a factor to your symptoms.

 

[Henry Boyd]

The water pickup plumbing on the BIII/496 is terrible. I was having the same problem a couple of years ago we replaced the water pump, thermostat and tightened hose clamps and nothing worked. Mercruiser suggested a through hull water pickup and provided all of the details (what an amazing coincidence!). The through hull is set up between the drive and the water pump with everything being isolated with sea cocks. We also added a valve for flushing. Have not had a single over heating event since.

Here is a pic of the original install. The gate valve has since been replaced with a bronze ball valve and boiler cap.

Henry