3.0LX Mercruiser always running cold

[Rugglesworth]

Hi everyone,

I have a 96 Grew bowrider with a mercruiser 3.0LX raw water cooled that never warms up. I bought this boat at the start of the summer. I have so far changed the oil, readjusted the choke, replaced the fuel pump and added a water/fuel seperator. She's running waaaaay better now.

Still, I noticed that the gauge wasn't moving over 120. I grounded the wire to the gauge and it pinned so I know the gauge is operational. I put in a new temp sender and still it's the same. I'm assuming it's a failed thermostat? Any one want to chime in?

Thanks!

 

[Scott06]

The thermostat would be the logical thing to replace the troubleshooting you’ve done so far

 

[Rugglesworth]

The thermostat would be the logical thing to replace the troubleshooting you’ve done so far

That's what I figured. Just not sure I can get one before I head to the cabin for 2 weeks. Am I going to do a lot of damage to the motor with it always running cold?

 

[Bondo]

That's what I figured. Just not sure I can get one before I head to the cabin for 2 weeks. Am I going to do a lot of damage to the motor with it always running cold?

Ayuh,..... It might run a litte rich,..... or not,......

To cold is Waayyy better than to hot,.....

 

[Rugglesworth]

Ayuh,..... It might run a litte rich,..... or not,......

To cold is Waayyy better than to hot,.....

That's my thought too for sure.

 

[Bondo]

Ayuh,.... Enjoy yer vacation,.....

 

[Rugglesworth]

Ayuh,.... Enjoy yer vacation,.....

Thank you I will!

 

[Scott Danforth]

Could just be a chunk of shell stuck in the thermostat

 

[Rugglesworth]

Could just be a chunk of shell stuck in the thermostat

This is also true however it's spent 99.99% of it's life in freshwater lakes. After doing the fuel pump, water seperator, new plugs it's running great however I after say running at 2000 rpms for awhile in a no wake zone and then when I accelerate it will sometimes bog for a second but not every time. I'm wondering if it's because it's running cold..... Too bad the marine supply stores in my area are super unreliable.

 

[Scott06]

This is also true however it's spent 99.99% of it's life in freshwater lakes. After doing the fuel pump, water seperator, new plugs it's running great however I after say running at 2000 rpms for awhile in a no wake zone and then when I accelerate it will sometimes bog for a second but not every time. I'm wondering if it's because it's running cold..... Too bad the marine supply stores in my area are super unreliable.

The bog is probably more carb rebuild related. You can see if it goes away after the thermostat.

 

[Lou C]

I have had this same problem, it is usually a bit of rust flake(s) that keep the stat from closing, then the engine will run at a cool 120* instead of its normal 160 unless I get it up on plane for a while. Even in freshwater you will get flaking rust on the inside of a raw water cast iron engine, it could be sand or silt as well doesn't take much.
Believe it or not I have on occasion cleared the problem by running it on plane, get it good and hot, and then stopping, bringing it back to idle & gently tapping the top of the thermostat housing with a small hammer, the vibrations sometimes frees the rust flake, etc.

 

[Rugglesworth]

I have had this same problem, it is usually a bit of rust flake(s) that keep the stat from closing, then the engine will run at a cool 120* instead of its normal 160 unless I get it up on plane for a while. Even in freshwater you will get flaking rust on the inside of a raw water cast iron engine, it could be sand or silt as well doesn't take much.
Believe it or not I have on occasion cleared the problem by running it on plane, get it good and hot, and then stopping, bringing it back to idle & gently tapping the top of the thermostat housing with a small hammer, the vibrations sometimes frees the rust flake, etc.

Thanks I will give this a try once I'm at the lake next Tuesday. Can't wait!