115HP 4 Stroke EFI Overheat Alarm

[dkeys]

Hello, I am new to the outboard world (plenty of years as a car mechanic) and have an issue with my 2012 115HP 4stroke EFI Merc overheating. Just bought the boat this year and all was well until about a month ago. I got an alarm and the engine pulled power. Earlier in the day I got caught up a bit on a sand bar but was able to push through. Was able to shut it down, then continue at moderate speed back to the dock. Looked at the tell tale and it was spitting, but not a steady stream. So I pulled the boat and replaced the impeller. From that time on I had a steady stream.

Put the boat back in the water and was running about. high speed for 5-10min, then no wake. When going back WOT, the alarm hit again and pulled power. Again, limped it back to the dock. Purchased a new thermostat and Vessel View mobile. Took it out with a mixture of high speed and no-wake without any issues. Water temp looked good.

Then today (the next time out), Once again, high speed no issue, then no-wake, then high speed again and the alarm. This time I had vessel view up to confirm it is a water temp. Temp was approaching 200F. Quickly dropped back down at idle. Opened it up again and it hit the alarm. Let it cool down and wanted to make one more pull with the motor trimmed down to see if that helped and it did not.

One thing I sort of notice after the alarm (after returning to idle), when I look back at the tell tale, I see some visible exhaust fumes near the water line that dissipate (not sure if that is relevant at all, but wanted to provide all info).

Does anyone have a diagram of the coolant flow for this motor? I plan on pulling the boat out of the water either later this week or early next week depending on weather. Any ideas as to what I should be looking for? I plan on doing a flush and seeing if I can get access to small passages such as the fuel cooler. Without an understanding of the coolant flow path, not sure how much a strong tell tale helps in this scenario.

Thanks in advance.
Daryl

 

[ufm82]

When you replaced the impeller did you also replace the entire housing or just the impeller? If you just did the impeller I would suggest replacing the upper and lower housings as they wear as well. The wear between the impeller and the housings can allow water to escape and not be pumped into the engine. Mine was susceptible to overheating at anything from 1800 to 3,000 rpm as the pump couldn't keep up with the load and I wasn't going fast enough to open the poppet. WOT was fine but coming down to no-wake speed would cause a temp spike.

 

[Texasmark]

I have no experience with that engine but on 2 strokers in that general HP range, they use a t-stat for speeds up to 2500 RPMS (service manual number) and water pressure above that speed unseats a "poppet valve" much larger in area for increased flow. Since you are experiencing high speed problems, time to look at your poppet.....if you have one.....if I read your post correctly.

On 2 strokers, the poppet and stat are under the same cover bolted onto the rear of the crankcase water jacket....encircling the spark plugs.

 

[dkeys]

When I replaced the impeller, I did replace the lower divider plate and the gaskets, but not the upper housing. If I have a steady stream out the tell tale, does that imply a good pump?

Not knowing the coolant path is a handicap for me right now. If I can find that, I'll be able to break down where the coolant is getting, and not getting so I can root cause why its not getting places.

Is there a poppet on the 2012 115hp 4 stroke?

 

[QBhoy]

Texasmark has a point here.

not familiar with your 2012 really...I have the newer 2.1l version. But wanted to ask if you had a flushing attachment like mine ? I’d try the hose on it and see if it makes a difference. Mine has a fitting on the upper side of it for doing just this. Maybe you do too.
other than that. Texasmark might be into something. Have a look at the TStat

 

[St1977]

My VesselView on my 225 has a water pressure gauge, does yours?

 

[dkeys]

T-stat has been replaced. No other valve in the housing. My vessel view has the ability to display water pressure, but there isn't a guage on the motor. I can add a manual gauge for root cause, it just wouldn't be on the bus.

 

[hl]

If your problem did not start until you ran into a sand bar, try back flushing from the thermostat housing down through the water tube. Drop the foot, remove the thermostats, run a water hose into the thermostat housing and flush with a light flow of water from the hose. You might need to use some tape to hold the hose in place.. You can use an old sock or t shirt to catch anything that comes out the bottom of the water tube. I did this years ago with an over heat problem and it seemed solved my problem then.

 

[dkeys]

Ok, finally got the boat out of the water and went through it. Pulled the lower unit and flushed out all passages on the motor. Pulled the thermostat and flushed down the dump tube. Put the t stat housing on upside down and used the dump tube to flush out the motor passages. Pulled the hoses from the FSM for cooler and insured they were free. Tell tale and exhaust port all free.

Then pulled the water pump back apart. A little sand in there but not much. Cleaned it up. The impeller had just been replaced. Water intake is clean. So I'm pretty damn sure the motor is cleaned out. Made sure I had a good silicone exhaust damn on the water pump block. I may not have had a good enough one prior.

Also, vessel view had reported a sensor issue but nothing more descriptive. I noticed the connector on the can sensor was broke. Now I'm wondering if the overheat was timing related. I ordered a new sensor up and hopefully that takes care of the fault.

Here's to hoping when I put the boat back in the water next spring I've got the overheat issue behind me. Thanks for all the input.