I had my first high temp alarm yesterday. I did a 1-hour maintenance run with no problems, then I drifted about 30 minutes while I worked on a bad tranducer. After that I headed up to the river to mark a few stump that takes out two or three skegs each season. Water pump has 57 hours and I never run it dry. The water temp was 89 in the shollow water and after about 5 minutes I got the solid beep. Water pressure was good, stream was good, so I spun the boat around and headed back to the ramp. As soon as I entered the deeper water the alarm went off. Total time was about 30 seconds. I;ve never seen the lake water that hot (10 degrees above normal), is the Water temp alarm that close to going off?

I have been in water temp (surface) in the hi 90's -100 and never had an alarm. I would suspect you maybe got something on the water pickups.

What motor is is? Seem slike some of the mercs have alot of trouble with popet valves causing cooling isues.

matt

I know a lakes water temp does some strange things to motors. I would more inclined to think you need to service the thermostats and poppet if your operating that close to high heat alarm.

if the poppet valve has not been changed do that first i have been seeing a lot of trash getting caught in them not allowing them to close completly thus letting normal water pressure in the block to escape it shows up more at idling a long time because at higher rpms you are getting more water in the block.

I wish I had tilted the foot to see if I picked up some weed or a plastic bag. I assume it was clear because there was a good stream of water comming out of the upper unit. I've never run the motor for an hour straight and never in high ambenent and water temp.

I understand that you can dammage the head gasket if the alarm goes off for more than 30 seconds. What are your thoughts.

I wonder if lower octain fuel would help?

I guess I need to:
1) Check all the in take holes for mud dobber nest.
2) Put the foot in a trash can and give it a good cleaning and check the water temp comming out. Should be around 180 to 190 to trigger the alarm. Take the temp up to 190 in the trash can and see if it triggers there or at a lower temp.
3) Mix remaining fuel with low octain.
4) Stay within trolling motor range of ramp until reloved .

If I get a second alarm, then:
5) Change the poppet valve (never changed).
6) Change the impeller (changed water pump only 58 hrs / 2 seasons ago).

I think lower octane runs hotter than premium.

more than likely impeller (water pump) needs changed mercury recomends every year now. i would check that first

99% of tha time its gonna be tha water pump and/or parts. No mater how old or supposed ta be new. Thats tha first thing that needs ta be changed with a heat problem. A "complete OEM kit" is tha only way ta go. Changing just tha impeller is like changing oil and leaving tha old filter on your car motor. Lake water temp shouldn't make any difference............jmo

Always change the impeller every year!

Thanks Guys.
Impeller pushing water out fine, I never run it dry, and it only has 64 hours and 16 months on it. Never the less the water pump rebuild kit is on order.
It would be an interesting test to see if higher octane runs cooler or hotter or no difference in the Merc RX-6. I know too lean runs hotter.
Noticed while reading up on the diagnostic procedures for the thermostats, temp senders, and poppets; that the water should not be hotter than 80 degrees, the thermostat is a 120 degree, and the sender is 164 degrees. I did not know that a Merc Rx-6 runs that close to sending a hot signal. I wonder how much is this to really protect the heads and how much is to prevent scalding water coming from the motor lower cowling?
Need to buy cheap thermal gun at harbor freight to check the thermostat and head temps (better than pencils). Looks like pulling and checking these six parts should take the better part of a � day to pull and test; take a few days to get the parts if needed, and another � day to install if needed. Manual says no need to replace the Thermostat, Popper, Sensor Assembly, or Sensor if they look good and test to spec; but if they are hard to pull, probably will replace anyway. Worse case cost for water pump rebuild and replace everything with OEM parts is less than $350.

Where did you get this information? Never have seen 120's in a "production motor" usually 143's. Sender should be 200+ and closer ta 240. Tha ONLY way ta know for sure is tha boilin' water test, as they can vary. Courious..............

JAN. Water pumps don't have a "shelf and/or hour" life....A good pee stream ONLY means there's water there. If its enough or not is not determined by this..........jmo

+1

Replaced poppet, thermostats, and impeller; problem gone. It was a corroded poppet. Now motor does fine in 91 degree water.

I took the temp of my heads on my xr2 with a laser pointer, and the temps varied quite a bit . If I recall the top right cylinder was abt 20 degrees colder that the bottom right.. same with left. motor was running on hose.
dont point the laser at the spark plug, point it on the head .