Mercury 25 EFI overheating

[bullshark98]

I've got a 2012 25hp model # 1A25213FK that overheats. I get the alarm and it goes to safe mode. I have installed a new impeller and t-stat. I have a temp gun and I'm showing about 215 deg when this happens at the head. I have double checked my impeller install, disconnected the oil sensor and still get the alarm. I'm getting flow at the tell tale. It's been in salt water and not always flushed.

Is there anything else I can check?

 

[Texasmark]

The tell tale may be plumbed off the exhaust manifold....which is a large rectangular plate on the left rear (Port) side of the engine.....that water is separate from engine coolant proper. My experience with OT warning sensors is 195F for alarm give or take sensor tolerances so it seems to be working properly. You said nothing about your thermostat. Salt water, corrosion, stat metal sticking when it needs to be functioning at 100-143F for opening temps I have experienced over the years.

If you haven't changed it lately, take it out and have a look at it and inside the cavity where it's located checking for corrosion buildup. You can put the stat in a pan of water on the stove with a candy thermometer. Pellet opening temp in F is usually stamped on the bottom of the pellet of the stat. You probably should change it anyway but still it would be good to know you found the smoking gun if it fails the stove test.

 

[bullshark98]

New Thermostat. I tried running w/o T-stat. I can go farther before overheating anyway. I do notice that the more I rev this thing, the less I have at the tell-tale. Wide open theres just a drop every now and then.

I tried flushing it out from the t-stat cavity with the foot off. I got water out of the tube, but did feel restricted. I could only crack open my garden hose, any more and it blew back on me. I also took a rod just thinking if any trash was in the tube I could knock it loose. I'm feeling rubber that gives, but nothing that will come out. Maybe a seal that protrudes into the tube?

 

[Texasmark]

Maybe a seal that protrudes into the tube?

Might pull up a parts list and look for a potential seal that could possibly beruptured: 2 places to look, where water tube exits the water pump...which you probably went over with your water pump repair and where the water tube enters the block.. I find the loss of tell tale at high rpms totally puzzling. Not a salt water guy so not much help there on gotchas.

I guess the next thing I would do, out of frustration, is to remove the 2 water jacket covers, the one through which the spark plugs extend and the one over the exhaust manifold and have a good look around, running water through cavities, checking the plumbing of the tell tale for foreign material. Pulling those two covers will expose a lot of the cooling system.

 

[bullshark98]

Thanks for the help Texasmark! For some reason the 3 online stores I checked do not have the parts diagram for my model.

I took it out again yesterday. I ran it at idle/ 1/4 throttle through a no wake zone for 15 min. Went to 3/4 throttle once I passed and 30 seconds later the high temp alarm went off.

I ran across 2 other guys with this same motor & issue on other forums. The seal at the top of the water tube had swelled blocking flow. I saw one comment saying common issue with this motor. I'm going to look some more though, maybe pull that cover you're talking about. I really don't want to pull the powerhead.

 

[bullshark98]

I pulled the foot off today, grinded a rod into a drill bit and used my cordless drill to get this rubber out. Cut until I didn't feel rubber anymore. When I flushed it out from the t--stat housing I had 2 pieces of impeller and a lot of small trash come out.

I took a test ride. 15 min wide open with no overheating. Hopefully it's good. Further testing tomorrow.