250 OX-66 Thermostats?

[Gary M]

Was running very shallow last week looking for lobsters so I 'may' have ingested some sand/muck/debris. Powered up to move and a minute later got a hot horn. Shut it down, let it cool off. Got ready to run home and it fired right up and ran great for two miles then the horn came back on. Water Pump is one year old with 50-60 hours on it and the pump was pumping fine through the pee hole.

A buddy suggested that the Thermostat might have gotten clogged or dirty and to pull it off and check/clean it. I've never done this but I'm handy with tools going back to my old muscle car (1970 Boss 302 Mustang!!) days, so I'm not afraid to look it over...... but I just have never done it.

Any advice or suggestions would be great! I'm hoping that some guy has posted a video showing this on YouTube!

Thanks in advance!

 

[Daman858]

Yep...same thing happened to me...my F200 has two thermostats. Easy change out. They were clogged with sand and would not open to allow water circulation.

 

[seasick]

Was running very shallow last week looking for lobsters so I 'may' have ingested some sand/muck/debris. Powered up to move and a minute later got a hot horn. Shut it down, let it cool off. Got ready to run home and it fired right up and ran great for two miles then the horn came back on. Water Pump is one year old with 50-60 hours on it and the pump was pumping fine through the pee hole.

A buddy suggested that the Thermostat might have gotten clogged or dirty and to pull it off and check/clean it. I've never done this but I'm handy with tools going back to my old muscle car (1970 Boss 302 Mustang!!) days, so I'm not afraid to look it over...... but I just have never done it.

Any advice or suggestions would be great! I'm hoping that some guy has posted a video showing this on YouTube!

Thanks in advance!

It is less likely that both t-stats would get clogged so the first thing ti try is to remove the cowling at the dock and start the motor. Using your hand or if you have it, an IR thermometer, measure the temps of each cylinder bank. They should heat up at about the same rate and will get fairly warm but not super hot to the touch. If they don't heat up evenly you may have an issue with one t-stat.
If they do heat up the same, it is probably not a t-stat issue.
If the motor overheats at low revs, you might have a stuck open poppet valve. If that is the case, the motor will not overheat at higher (cruising) revs. The valve is fairly east to remove but make good notes of the order of parts, direction of them and where springs etc. go.
So if it overheats at speed and the t-stats seem to be working, you may have a clogged or damaged water pump.

Now if you had general buildup of crud in the water jackets, the issue with possible sucking sand may have been enough to cause a blockage in the water chambers.
Usually, removing the t-stats will allow you to see if and how bad the buildup might be.
Finally, if you replace the t-stats, replace both and use new gaskets ( included in some kits). Do not over tighten the housing bolts, they can break. Go easy, a torque wrench is the best approach but feel works OK if you have experience in general with not over tightning bolts,

 

[GreatWhite23]

If it is not overheating check the oil res. sensor on the motor. They go bad and are frequently the cause of the alarm

 

[seasick]

If it is not overheating check the oil res. sensor on the motor. They go bad and are frequently the cause of the alarm

Assuming the vessel has digital displays, there are different alarm symbols for low oil and overheating. There should be no confusion.