Overheating Merc 250 4s

[bhodgedds]

Join DateFeb 2015Locationhendersonville tnPosts38

Merc 250 4s 5800 rpm

3B048831 sn 21 merc pro xs 4 stroke

Join DateFeb 2015Locationhendersonville tnPosts38

Merc 250 4s 5800 rpm

3B048831 sn 21 merc pro xs 4 stroke

About a month ago alarm sounded on take off and engine went into protect mode. Shut down and restarted and it was fine. Was on my 3rd week fishing chicamauga so I thought it might be grass. Took it to dealer and they put it on computer. Said I had 5 overheats in last .2 hours. I only heard the alarm the one t
ime. They said they removed lower unit and all checked out ok. They said Mercury “wasn’t much help” so they replaced the water pump and declared it fixed.
I ran it a couple more days after that.
took it to a different dealer closer to home to check on computer after last day of fishing to check on computer and they said no new codes.

today, water and air temp 60. I was watching temp on smartcraft each time I ran. First couple runs were fine. Short .1mile runs. Then on one run temp ran up to 199. No alarm. I backed to neutral and it died. Restarted engine and temp stayed at 138 the rest of that run. Next run it was 138. Then the next run temp ran to 203. I kept going to see if alarm would sound. It didn’t. But the temp began to run back down to 138.
What are your thoughts?

[Tfall]

Thermostat issue maybe?

[bhodgedds]

Don?

[EuropeanAM]

If the impeller and BOTH gaskets are intact, and there is no debris in the water inlet area/passages, I would be cleaning the strainers (3) and replacing the thermostat.

Do you have a water pressure sensor installed so that you can monitor pressure AND temp?

[bhodgedds]

I have smartcraft to monitor temp. Only have guage to monitor water pressure and it’s been above 20.

[EuropeanAM]

Logical to move to strainers and thermostat, then.

[bhodgedds]

Dealer says they cleaned strainers and “checked” the thermostat and it opened while running on muffs. “Therefore it will always open every time”.. I have asked them to replace thermostats under warranty or give me a price to replace them. This is so frustrating. Back and forth. They hate it when I suggest something, “quit reading stuff on the internet “, which I can kinda understand. I don’t really want my patients telling me how to fix their teeth. But week after week of taking it in, picking it up, running it, then taking it back. 40 hours on it.

[EuropeanAM]

Thermostats are considered a maintenance item- so probably the smart thing to do there is to buy one (as well as the required oetiker clamp) and install it.

I can certainly feel for your dealer's take on "been reading on the internet". There's way more useless banter out there than there is helpful/constructive information.

BTW... that 3rd strainer is hidden underneath the port-side (lower) cowling. Can't be accessed without lower cowl removal.

[bhodgedds]

Don would a thermostat possibly work correctly most of the time, but on an occasional run stick?

[EuropeanAM]

Certainly a possibility. And perhaps one of the easiest items to replace and rule out.

[bhodgedds]

At what temp would the engine record a code?

[EuropeanAM]

That depends on several factors that are pre-programmed into the PCM Calibration.

BTW... does your warning horn sound a test beep at key-up (without touching the trim before hand)?

[Bowenbass20]

What is considered" normal " run temperature vs "overheating" temperature?

[EuropeanAM]

120-185F is generally accepted as the expected temperature range.

Thermostat is supposed to be fully open by 170 degrees, so if the ENGINE temp (NOT OIL TEMP) starts climbing and exceeds 185F I would be looking to determine WHY.

[bhodgedds]

That’s a good question about the horn beep at start up. It did at first. Then I noticed it wasn’t. Maybe after it coded? The dealer had it to troubleshoot and I noticed after it beeped again. Does that make sense? Can you explain why it would?
this dealer doesn’t want to fool with troubleshoot anymore. Said they tested thermostat and it opened. So I asked him to replace stats He said $250. Ordered parts.
I’ll pay it. Gotta rule it out.

[EuropeanAM]

Warning Horn sounds at each key-up UNLESS the trim switch has been activated (which wakes the PCM, thus affecting the Horn-Test sequence since the PCM is already awake).

It is possible that the horn was disconnected (previously) or had a bad connection.

[bhodgedds]

Heck Don, I really don’t think it was disconnected. I thought maybe after it triggered the alarm it wouldn’t beep at startup to maybe let you know it had coded. But I was fishing grass in November and trimmed motor up at each stop to keep it from dragging in weeds. Most likely trimming down on startup! I was thinking I wished they had presets where you could press one time and motor would trim to set position. You could make some money w that idea.

[EuropeanAM]

Interesting thought.

[bhodgedds]

Is there only one thermostat on the 4s?

[EuropeanAM]

Yes.