2002 Mercruiser 3.0L thermostat replacement

[mefferz]

Hello,

I have a 2002 Sea Ray 176 Bowrider with the Merc 3.0L carbed motor. I bought the boat last season and decided to do a few maintenance items since I didn't know when they've been changed last. Normal operating temp for the boat has been around 170-175F on the gauge. I pulled the old thermostat and 160 is stamped on the bottom. I ordered the Sierra 18-3647 kit with gaskets and replacement 160 thermostat. Before I installed the new stat I boiled it to make sure it would open and it did. I installed the Sierra stat and ran the motor on muffs for 10~ minutes and the temp started creeping up to 200~F before I got nervous and killed it. I popped the old stat back in and she idled normally at 175F.

Anyone have experience with Sierra thermostats not opening at the right temp? Should I just go with OEM Merc?

 

[alldodge]

Hello,

I have a 2002 Sea Ray 176 Bowrider with the Merc 3.0L carbed motor. I bought the boat last season and decided to do a few maintenance items since I didn't know when they've been changed last. Normal operating temp for the boat has been around 170-175F on the gauge. I pulled the old thermostat and 160 is stamped on the bottom. I ordered the Sierra 18-3647 kit with gaskets and replacement 160 thermostat. Before I installed the new stat I boiled it to make sure it would open and it did. I installed the Sierra stat and ran the motor on muffs for 10~ minutes and the temp started creeping up to 200~F before I got nervous and killed it. I popped the old stat back in and she idled normally at 175F.

Anyone have experience with Sierra thermostats not opening at the right temp? Should I just go with OEM Merc?

:welcome: to iboats

While I like OEM (Merc and GM) parts better, I don't see an issue with the thermostat. It could be bad, but this would be out of the norm. It could be you have a gauge issue, or it could be just running the engine on muffs. You should not run much above 1000 rpm. To really tell you should run the engine in the water. IMO muffs are just for quick checks not for actual status runs

 

[airshot]

Had the same issue this spring....bought new stat and they only had the sierra in stock so I took it. I normally try to use merc parts, when I started it up it climbed up to 165 and I shut it down, now mine is a 140 degree stat so......let it cool then put the old one (merc factory) unit back in and presto right back to 125. Not worth the gamble on aftermarket parts to me to save a couple bucks. Never had an issue with factory parts..

 

[mefferz]

:welcome: to iboats

While I like OEM (Merc and GM) parts better, I don't see an issue with the thermostat. It could be bad, but this would be out of the norm. It could be you have a gauge issue, or it could be just running the engine on muffs. You should not run much above 1000 rpm. To really tell you should run the engine in the water. IMO muffs are just for quick checks not for actual status runs

Thanks for the welcome!

The Sierra thermostat has to be bad or mislabeled. I tested both while running on muffs and only the Sierra one overheats the motor. I put the old OE Merc stat back in within 2 minutes of testing the Sierra stat, started the motor back up, and the temp held steady at 175 so I can't blame the muffs.

 

[mefferz]

Had the same issue this spring....bought new stat and they only had the sierra in stock so I took it. I normally try to use merc parts, when I started it up it climbed up to 165 and I shut it down, now mine is a 140 degree stat so......let it cool then put the old one (merc factory) unit back in and presto right back to 125. Not worth the gamble on aftermarket parts to me to save a couple bucks. Never had an issue with factory parts..

Good to know. Thanks for the input!