2001 Mercury Mariner 50HP 2-Stroke HIGH temperature alarm

[Gulfsurfa]

Hi everyone,
I have a 2001 Mercury Mariner 50HP 2-Stroke oil injected motor. I took it out last Saturday and when WOT, I got a steady beep indicating high temperature. I slowed down and the beep stop, however later into the day I received the steady beep when trolling and even while on idle.

I removed the cowling while running the motor at EXTREMELY low RPMs and felt the tell-tale which felt warm (normal) but no where close to hot. I started noticing smoke out of the exhaust and maybe a little more than usual. While running, the top small water hose blew off dispersing water from the top of the motor. That water was boiling hot and I instantly turned off the motor, put the hose back on whith a new zip tie. Obviously high water pressure caused the hose to blow off but cannot seem to figure out what is wrong.

I bought the motor used and replaced the water pump (impeller), spark plugs, and added a water separating fuel filter. I ran the boat for about 15 hours with no problems. Any help you guys can provide is GREATLY appreciated. I called my local marine mechanic and they want 200 bucks just to drive it to the lake to replicate the issue! The motor is used in salt water.

 

[Maxz695]

Re: 2001 Mercury Mariner 50HP 2-Stroke HIGH temperature alarm

If this has a thermostat replace it. It is not opening. it also has a baybass i believe that will allow some flow even when not opening.

 

[Gulfsurfa]

Re: 2001 Mercury Mariner 50HP 2-Stroke HIGH temperature alarm

OK I have the manual so I'll check on if/where the t-stat is. I did read your post for someone else about replacing the entire water pump with a kit instead of just the impeller as the housing may get "groved" after a while.

Is this worth replacing myself and also checking the LU for any debris?


Thanks for all your help

 

[Gulfsurfa]

Re: 2001 Mercury Mariner 50HP 2-Stroke HIGH temperature alarm

I just hope I didn't cause any further damages while running it overheated. I did let it sit for about an hour...and fired it up to get it from my dock to the boat ramp and it turned over the first time and seemed to run ok until I got to the ramp. While idling, the alarm started again. I did clear the tell-tale line and also the line where the hose originally blew off. I used a small wire to clear any possible blockage up as far as I could reach.

I'll check the t-stat (if I have one) tonight...while I'm doing that is there any where else I can check for possible blockage?

Would an oil distribution be a possible issue? The resivoir is full and I had it out for about 4 hours...I wonder its not getting enough oil/gas mixture?

 

[Gulfsurfa]

Re: 2001 Mercury Mariner 50HP 2-Stroke HIGH temperature alarm

OK I solved the high temperature alarm and Maxz695 you were right on the money. I replaced the entire thermostat kit (gasket, t-stat, carrier, seal). Dropped it in and the alarm went away. I couldnt believe how bad of shape the old one was. It was actually broken keeping the popet closed.

Many thanks! This is my first boat and I've had it for a little over a month. Definitely gratifying when you can fix these kind of things yourself and save a huge ammount of cash. Marine repair wanted $300+...my cost was $43.75 and took about 45 minutes to replace. I had to wait about a week until the parts came in so that is why I'm just posting now.

Just to ensure i didnt warp any heads I ran compression on all 3 heads and they were reading 125+ which was exactly the reading before I bought the bought so that was also a HUGE relief!!