250 ProXS 4S - Overheat Alarm: Need tips for assessing issue

[marshall256]

Model #: 12500033A
Serial #: 2B647728
Hours - 120

At the end of the day yesterday, I was attempting to load my boat on the trailer when I got a long solid horn/alarm. Similar to what I've always heard on all my other Merc's to be an Overheat alarm. I turned the engine off. Checked my smartcraft monitor, I have the small square gauge. Oil temp was like 190 and water temp was 200. Yep it was HOT. Trimmed engine up to check for something blocking the water pickups. All was clear. Trimmed motor back down and cranked the engine. No alarm and I proceeded to navigate my boat to the trailer. Then, alarm sounded again, but after about 1 minute or so it stopped. My thinking was, I'm at my trailer and blocking up the ramp, let me get her loaded and then I assess the situation. I did check the Pee stream and it was peeing but looked a little weak. As I attempted to power onto trailer...it seemed like it would drop out of gear. Basically, all I could do was slow idle...so I assume it dropped into guardian mode. Made it to trailer and winched it up onto the trailer. I didn't find any debris plugging any of the water intakes when I inspected at the ramp. I wasn't driving through any grass during the day. But, the river was a little rich with debris yesterday along with some heavy thunderstorms that forced me to shelter in a shallow creek for a while. My run to the ramp was a 20 minute run though and no issues during the run with overheat alarm.

So, I'm thinking I've got some work to do to figure out the cause of the overheat. My 250 ProXS has been flawless and I've only removed the cowling to date to change the oil filter and fuel filter which was done at 100 hours (20 hours ago). Any tips on next troubleshooting steps? I'm not too bad at fixing things myself unless it involves being hooked up to a computer. Assuming a good flushing of the engine would be step #1. But, also wondering if I should look at the thermostats to make sure no debris is hung up in them. Although, this is my first 4 stroke and I don't have a clue as to where the thermostats are located on this engine.

[sblnchrd]

water pump gasket probably blew out know problem with these motor but also check the 2 water pump filters under the hood

[marshall256]

Update: Checked the 2 filters on the rear starboard side of the engine and both were really clean. I'm hearing there is another filter on the Port side of the engine, but it's in the mid-section and you have to remove the mid-section cowl. I'll have to put some thought into how to get the mid-section cowl off. Most of the bolts are straight forward, but I'm struggling with the bolt in the front just below the upper cowling front latch. That dude is a PIA to even see.

[Bluzharp]

1/4" drive, 12" extension, a universal joint and a 8mm six point socket will git 'er done. I was just into mine to check the lower strainer which was fine. It's not overheating but the pressure seems low. The gasket really holds the cowling tightly. A bit of soapy water helps a bunch when reinstalling.

[sblnchrd]

water pump gasket u probably overheat at idle than when u takeoff temp drops due to water pressure to motor mine did the same thing it was the water pump gasket that. blew out check that first

[mikesxpress]

Chris if your engine strainers were clean it's highly unlikely the one inside the clams is plugged. Most likely the water pump as already noted.

[marshall256]

Chris if your engine strainers were clean it's highly unlikely the one inside the clams is plugged. Most likely the water pump as already noted.

Yep, I had the same thought. I haven’t serviced the water pump to date. Might as well go ahead and service it.

[EuropeanAM]

Two important items:

-Warning Horn: A SOLID TONE warning horn is an indication of a CRITICAL FAULT. It means you should shut the engine down as soon as safely possible, and get it in for service. DON'T continue to run the engine beyond what is reasonable to safely shut down... it's PCM is recording how many seconds the engine continues to run (and may record other data if Guardian is active).

-ANYTIME you have a cooling system problem, or an overheating problem, ALWAYS, ALWAYS start at the SOURCE: The Water Pump.