2004 115hp over heat help

[2swift]

I went out to the Island yesterday and about 2-3 min into cruse I got an hot light and buzzer at the same time it dropped PRM's I'm guessing as a protective measure. I have just recently replaced the water pump an T Stats trying to rectifie the same issue. So today I pulled the heads to inspect them hoping to find a blocked water passage or something but all looked ok to me. I did see something that did not look right so I'm here for help. What caused my pistons to look like this? Anyone? Thanks Pat

 

[2swift]

Re: 2004 115hp over heat help

 

[ob]

Re: 2004 115hp over heat help

Assuming you are running the factory recommended spark plugs at the recommended gap setting I'd next suggest that you insure that the engine is propped correctly to allow it to achieve the factory recommended rpms at full throttle with an average load aboard.Overpropping and engine is but one item that can lead to coking of the cylinders and pistons.

 

[2swift]

Re: 2004 115hp over heat help

Assuming you are running the factory recommended spark plugs at the recommended gap setting I'd next suggest that you insure that the engine is propped correctly to allow it to achieve the factory recommended rpms at full throttle with an average load aboard.Overpropping and engine is but one item that can lead to coking of the cylinders and pistons.

Plucgs are factory spec.Please if you can define coking? I was thinking some kind of delamination on the pistons as the spots you see in the pics are the clean surface of the piston with no carbon..
As to Prop it's OE I think but don't quote me on this 15 by 17? Thanks for the reply!

 

[ob]

Re: 2004 115hp over heat help

Coking: excessive carbon /plaque buildup. Difficult to advise any further without knowing the specific 115 engine in question here. Carbureted , fuel injected ,etc... Please list model number of engine.

There are a wide variety of prop diameter and pitch applications for each outboard engine.The length ,style,and weight of each boat will dictate which prop will be best suited in order to attain optimal performance and engine longevity.No such animal as an OE propeller in my world.

 

[2swift]

Re: 2004 115hp over heat help

Coking: excessive carbon /plaque buildup. Difficult to advise any further without knowing the specific 115 engine in question here. Carbureted , fuel injected ,etc... Please list model number of engine.

There are a wide variety of prop diameter and pitch applications for each outboard engine.The length ,style,and weight of each boat will dictate which prop will be best suited in order to attain optimal performance and engine longevity.No such animal as an OE propeller in my world.

Thanks again for your time.
I'm running 2003 19' Seaboss with a late model 2003 Johnson 2 stroke model #J115PXSTS At WOT she will do 5400 RPM with 2 adults 2 kids and 50 gallons of fuel not to mention the cooler at 96 c capacity..

 

[ob]

Re: 2004 115hp over heat help

In my opinion and assuming that the 5400 rpm you listed is with the engine trimmed out,I'd recommend you shoot for 5700-5800 rpm at wide open throttle.This will lower engine load and cylinder temps.This can be attained by either re-propping your engine and /or raising the engine height on boat transom of your current setup.This is assuming your engine is currently static mounted without a jackplate.If you are intersested in getting the most out of your engine performance and also increase longevity by attaining an optimal setup I'd recommend you begin a new thread in the prop forums.There are some savvy guys that frequent there that are experts at that very thing.

 

[2swift]

Re: 2004 115hp over heat help

In my opinion and assuming that the 5400 rpm you listed is with the engine trimmed out,I'd recommend you shoot for 5700-5800 rpm at wide open throttle.This will lower engine load and cylinder temps.This can be attained by either re-propping your engine and /or raising the engine height on boat transom of your current setup.This is assuming your engine is currently static mounted without a jackplate.If you are intersested in getting the most out of your engine performance and also increase longevity by attaining an optimal setup I'd recommend you begin a new thread in the prop forums.There are some savvy guys that frequent there that are experts at that very thing.

I am very interested in get maximum bang for the buck but at this point after 5 years of no issues other then electrical I have to go with rectifying this problem first.

 

[ob]

Re: 2004 115hp over heat help

I wasn't clear from your original post whether you had replaced the waterpump and T/stat to no avail of the overheat problem or whether the head removal and inspection was part of the same.I assume that the old impeller was completely in tact and no pieces of rubber were missing that could have gotten lodged within the water passages.I'm also assuming that the spring loaded bypass feature of the t/stat assy. is in good and free working order.Water intake screens clean and clear?Readers only have as much info as you supply.Other than the alarm and engine going into S.L.O.W. mode which limits the rpms in an overheat situation,have you actually touch checked or used a thermo-melt stik on the head covers to verify an overheat? The reason I ask is that while the temp sensors of your engine are inherently reliable,they do occasionally malfunction.

 

[2swift]

Re: 2004 115hp over heat help

I wasn't clear from your original post whether you had replaced the waterpump and T/stat to no avail of the overheat problem or whether the head removal and inspection was part of the same.I assume that the old impeller was completely in tact and no pieces of rubber were missing that could have gotten lodged within the water passages.I'm also assuming that the spring loaded bypass feature of the t/stat assy. is in good and free working order.Water intake screens clean and clear?Readers only have as much info as you supply.Other than the alarm and engine going into S.L.O.W. mode which limits the rpms in an overheat situation,have you actually touch checked or used a thermo-melt stik on the head covers to verify an overheat? The reason I ask is that while the temp sensors of your engine are inherently reliable,they do occasionally malfunction.

Impeller was 100%...Way ahead of ya Capt'n
I have tested both heads with a temp gun and they came within spec's... flow is real good. it's the clean spots on the he pistons that concerns me.Is it from water flashing? As to the temp sensors well...

 

[ob]

Re: 2004 115hp over heat help

So the overheat issue is history??? As for the chips of clean spots on the piston crowns,since they all appear to be on the perimeter of the pistons near the cylinder walls,I'd have the deduce that they simply chipped/sloughed off due to normal piston slap and not water intrusion.Bare in mind that such excessive deposits will retain cylinder heat and inhibit proper heat transfer from cooling system.Which brings us back to square one.The cause of the piston crown coking.Which is likely due to engine being excessively loaded due to a possible propping issue,fuel/oil ratio issue,ignition,ect...That's my 2 cents and I'm getting short on pennies.

For what it's worth,that engine looks to be mounted too low to me.Anti-ventilation plate should be at to just above the mean boat pad as a starting point.

 

[2swift]

Re: 2004 115hp over heat help

So the overheat issue is history??? As for the chips of clean spots on the piston crowns,since they all appear to be on the perimeter of the pistons near the cylinder walls,I'd have the deduce that they simply chipped/sloughed off due to normal piston slap and not water intrusion.Bare in mind that such excessive deposits will retain cylinder heat and inhibit proper heat transfer from cooling system.Which brings us back to square one.The cause of the piston crown coking.Which is likely due to engine being excessively loaded due to a possible propping issue,fuel/oil ratio issue,ignition,ect...That's my 2 cents and I'm getting short on pennies.

For what it's worth,that engine looks to be mounted too low to me.Anti-ventilation plate should be at to just above the mean boat pad as a starting point.

Thanks fer all the help but the saga will have to continue. I have to sleep! Old Mercs rule!

 

[2swift]

Re: 2004 115hp over heat help

 

[ob]

Re: 2004 115hp over heat help

 

[2swift]

Re: 2004 115hp over heat help

I Might have found the problem....I think but don't quote me.
I think my port Temp sensor with fast start temp sensor is failing in a weird way...Vibration related...as they have been tested and passed 2 times at a shop..
More soon.

 

[2swift]

Re: 2004 115hp over heat help

Today we ran the boat with a loaner port temp sensor and all is well in the world.
Best we can figure is the port sensor having a dual purpose "Quick start temp & overheat temp" Has failed.
It will test normal in oil at 105 for Quick start and at 240 for the overheat but still fails under "normal" operation above 3700 rpm....Best guess is it's harmonic vibration on an already weak sensor.