over heat alarm 2005 Mercury Optimax Saltwater 150XL

[Acadianwife]

Newbie alert and female at that. Now that boating season is coming back, i am trying to diagnose my over heat alarm. We bought the boat last year it ran fine first time in the water. As a precaution we dropped the L/U and changed the impeller, 2 gaskets, and the lower unit gear oil, which looked fine. took the boat to a local fresh water lake and the alarm went off after 5 minutes of running at 1800-2200 rpm. Backed off the engine to idle and alarm stops, go along our merry way for the rest of the day. The boat is pissing strong, and this problem happens like clockwork. The engine is fine at 2500 rpm to WOT and Idle-1500. So since the engine was fine before we dropped the L/U to change the impeller...we dropped the L/U again today and everything looks fine except we pulled the water pump base and there quite a bit of sand/corrosion/ orange paint? and the bottom gasket was swelled on the spots that were not compressed. Would something as simple as changing out the whole waterpump base, o-ring, and bottom gasket really make that much difference? The guy we got the boat from mainly used it in the gulf of Mexico alas the white sand. Thank you for any input, and yes we have a Mercury Service manual serial number 0G960500 and above

 

[CharlieB]

Re: over heat alarm 2005 Mercury Optimax Saltwater 150XL

If either housing of the pump is warped enough to NOT compress the gasket then once the boat gets 'on plane' raising the gearcase the waterpump is no longer submerged, and air can be sucked into the pump housing, less water pump output, and your motor overheats.

 

[Acadianwife]

Re: over heat alarm 2005 Mercury Optimax Saltwater 150XL

Thanks for the reply. So it may just be the whole housing needs to be replaced? That is what I was planning on doing, going to the mercury dealer today to get parts. Do you think it may be a trim problem? Like I say I am a newbie and I wouldn't be suprised if it is user error, I had a prev post last year and it was the trim.... changed the way i drove the boat, but now this other issue.

 

[Maxz695]

Re: over heat alarm 2005 Mercury Optimax Saltwater 150XL

i,m in fl and go out to the gulf near sarasota. I was having waterpump issues so I bought the COMPLETE waterpump kit with the base. Still waiting on it but i at least can rest knowing all is good and i,lll just have to do the impeller next year

 

[rovmike]

Re: over heat alarm 2005 Mercury Optimax Saltwater 150XL

Replace the whole thing if there is any question. The cost of a water pump housing is nothing compared to a blown powerhead. A little tip if you are not doing already. Cover the impeller with dish washing soap before installing. Makes it much easier.

 

[jeffersondodson561]

Re: over heat alarm 2005 Mercury Optimax Saltwater 150XL

Anytime you suspect any part of an impller assy. float test it. If you are certain your impeller is good, next place I would check is here (#12), follow the grey hose to the block and check for restriction at the block and at the sensor. If problem does not go away, next check the thermostats and pressure relief valve. Good luck...and BTW the way to perform a float test is to throw it in water and if it floats, it's good if not it's bad (not to be used with carburetor floats) similar to SWT's.

 

[jfscpa]

Re: over heat alarm 2005 Mercury Optimax Saltwater 150XL

My motor had the same problem and all I had to do was replace the sensor above the water pump. This sensor reads water flow and was bad, thus was sending a low flow code which cause the motor to think it was overheating when it wasn't and then it caused the overheating alarm to sound. Now it is replaced, the code is gone. Dealer found and fixed the problem.