Smartcraft thermostat fault on 2011 OptiMax 250

[Frank O]

I have a 2011 OptiMax 250 that was delivered around New Year's, and just has a few hours on it. Today I ran to the fuel dock -- a four-mile round-trip at ~5 knots. As I was returning to the slip at the end, I heard a single beep and the Smartcraft tachometer's digital display showed the warning "Sys Fault - Thermostat." At the time, the engine water temperature was ~145 F and the water pressure seemed normal.

Can anyone explain what exactly this fault means? It also happened a few weeks ago when I was running the outboard in the slip. I gather that this fault does *not* signal an overheating condition. Rather, I gather that somehow a sensor detects that one of the thermostats isn't opening (or closing?) when it's expected to. Is this correct? Can anyone explain more about how the sensor that detects this works? If it keeps happening, I guess I could pull the thermostats to see if one is sticky. But I'd like to understand better how the sensing circuitry works.

 

[Rubixone]

Re: Smartcraft thermostat fault on 2011 OptiMax 250

well I am not positive and with newer tech they may have changed how things work but traditionally there is a heat sensor that reads the temp of the engine block and when that gets to hot you get a reading like that saying there is a bad thermostat, you say "thermostats" you have two? thats also odd, does you motor have a ECM, if so have a mechanic with Diacom marine software test it....

 

[Faztbullet]

Re: Smartcraft thermostat fault on 2011 OptiMax 250

There are sensors on the head that monitor the head temps but not the actual stat. It sounds like you have a t-stat with a piece of debris in it or its sticking slightly open causing engine to run to cold on that side and that will trip this error...

 

[Frank O]

Re: Smartcraft thermostat fault on 2011 OptiMax 250

Thanks for the replies. A temperature mismatch sounds plausible. I might get the engine up to higher rpm to see if this helps the thermostat get unstuck (it's been run at harbor speed primarily lately). If the error recurs, then I probably need to pull the t-stats.

Just to clarify a couple of points -- this is a different error from the basic overheating error. If the engine overheats, the screen would display "Overheat." This, on the other hand, is a "Sys Fault" error. The manual says, "The 'Sys Fault' bar indicates there is a problem in the system. 'Show' displays the faulty component" ("Thermostat" in my case).

Regarding the number of thermostats, my old Merc V-6 carbureted 2-stroke had one t-stat per set of three cylinders, and I assumed it's the same on this newer engine. My old outboard only had one temperature sensor in the block covering the entire engine. If a temperature mismatch between the two sides of the engine is the cause of this fault, I guess the newer engine must have two.