2018 Pro XS 150hp Thermostat removal

[Mitriton]

<2B578744>

I would like to remove the thermostat to check for proper operation because even with 90 degree water the smartcraft never reads beyond the 130's in temp. I don't know what the operating temperature should be, can someone inform me please? During winter (50's for water temp) it stays in the mid 120's at full throttle and drops down into the teens during idle. It has about 215 hours on it. Can I remove and replace the thermostat without a new gasket? It's a 2018 Merc 150hp ProXS

[EuropeanAM]

2B758744 does not match your description.

On the 150 Fourstroke, the thermostat is mounted directly atop the powerhead. Quite simple to replace- recommend ordering a new thermostat AND the oetiker clamp.

If there is debris in the thermostat, it's relatively easy to disassemble and remove the debris.

You can view the thermostat in the parts diagrams on our website at: www.mercurypartsonline.net

(Cooling System Section). #2 and #30 are what you would need (of course, using the correct serial number to look it up).

[Mechanic Bob]

I did mine and as Don said it was very easy to replace! I also ordered and replaced the screen / filter. Kept the parts I removed for spares as those were still in good shape. Just needed a good cleaning.

[MichaelJ3]

Removal and reassembly is super easy, have removed and inspected mine several times.

I will say this engine doesn’t run very warm, at least mine doesn’t. Even on the warmest days, with mid summer warm water, I rarely see temps in excess of 125 on my Smartcraft.

Don, what is the “open temp” of the 150 4s thermostat? Must be about 125?

[EuropeanAM]

Correct- should be beginning to open by 125 degrees.

[Mitriton]

Thank you all for the replies. I'm a little more at ease on the matter. And I will recheck my serial number.

[Mitriton]

Don, you were right. Serial number for the outboard is 2B578744. I had the 7 and 5 reversed. I know where the thermostat is, I was just wondering if I would need a new housing gasket if I remove the housing to look at the thermostat, or if there's even a gasket there. Thanks again.

[MichaelJ3]

Don, you were right. Serial number for the outboard is 2B578744. I had the 7 and 5 reversed. I know where the thermostat is, I was just wondering if I would need a new housing gasket if I remove the housing to look at the thermostat, or if there's even a gasket there. Thanks again.

Service Manual says to inspect it and lube it w/ 2-4-C before re-insertion, I have done this 2-3 times and never had to replace the O-Ring on the Housing.

BTW, I highly recommend ordering a service manual from Don for your engine, answers a LOT of these easy questions, and many more complex ones.

Don, it is interesting how the Service Manual explains how to disassemble the thermostat and spring out of the housing, but the thermostat itself is not available without buying the whole housing...but then again, guessing the whole thing isn't too expensive preassembled, and then replace, so I guess doing all the pieces makes sense if its time.

[EuropeanAM]

Thermostats aren't particularly cheap... but in many cases, simple disassembly and removal of debris that is lodged in the seat may solve the problem.

If the PIN in the thermistor does not retract and allow the valve to seat- it's time for a new thermostat.

[Mitriton]

Thanks again gents.

[Mechanic Bob]

When I ordered my Thermostat, I ordered a new O-ring too. The new Thermostat came with the O-ring. So I have an additional O-ring. But it was cheap insurance to order the O-ring, just in case. (FYI, There is a rather long lead times on these parts.)