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2002 Mercury 50HP ELPT0 - Hi Temp Alarm with scalding hot tell tale water

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fickesd1

New member
Here is the situation that I need help on. I have a 2002 50 HP Mercury outboard that starts right up but after a few minutes of idling the hi temp alarm goes off. Water is coming out of the tell tale at what appears to be normal pressure but it's coming out scalding hot and engine block is too hot to touch. I removed the thermostat and put in boiling water and it seemed to work. One thing I noticed when I removed the thermostat was that there didn't seem to be any water residue in the opening where the thermostat goes. Is that normal? I also ran the engine with the thermostat removed expecting to see water coming out the opening but nothing came out. Should water come out that hole?

The only other thing I can think of is if the oil injection failed causing high friction and heat in the cylinders. How would I know if that failed? Any other suggestions on what I should be looking at next? Thanks in advance for any help you can provide
 
Did you put a new water pump impeller in in the last year / last season ?-----Compression test is the first thing to be done now.-----Ever run the motor without cooling water to the impeller ?-----I know for a fact that people are still doing this !!-----Mix gas and oil at 50:1 until you confirm oil injection is working !
 
I have not put a new water pump impeller in but the stream from the tell tale doesn't look too bad. I will try a compression test tomorrow when back at the boat. The boat is a pontoon boat and it's rented out as part of the vrbo rental so I don't always know of the misuse from the renters. I have mixed oil in the gas as a precaution but not sure if it's run long enough to get to the engine. I was planning on putting a small amount of oil in each cylinder to make sure. I will check compression first and then put the oil in each cylinder to help lube it up. Thanks for the suggestions. Would you happen to know if water should be coming out where the thermostat goes if I remove the thermostat and run it for a minute?
 
If the 2002 50 hp is like the 2002 90 and 115 hp engines the tell tale is plumbed directly off the exhaust manifold cover and the exhaust manifold water jacket gets water flow with no blockage as long as the engine is running. Folow the tell tale hose back to the source. .....edit footnote after rereading your proplem: Yours may be plumbed off the main block cooling....regardless your tstat is stuck shut is my best guess. 195F is certainly scalding hot water....steaming hot almost boiling at sea level...212F.

On the other hand, the engine block water...around the cylinders, is temperature controlled to around 120-145ish range. If the thermostat is stuck shut...which I'd say yours is, the block water gets up to around 195F where the OT alarm, located in the block water jacket (back where the spark plugs are located on the bigger engines for sure) and grounds the low side of the horn and it blows.

I don't know where yours is located. On my engines, it's in the upper left corner of that plate under a double dimple cover....larger engines use a pop off valve for higher speed additional cooling so there are 2 dimples....yours probably only has the tstat.
 
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