Wrong Thermostat Installed?

[problem child]

I just purchased my first boat, a used 1997 Caravelle Interceptor 212 and I believe someone may have installed the wrong thermostat. I do not have an overheating problem, but I may have an under heating problem. The temperature never gets above 145 degrees even when cruising, so I assume it has a 140+/- thermostat installed. All of the literature I have found (product application guides, Mercrusier manual #17, etc.) seems to indicate that I should have a 160 degree thermostat. However, others have said the thermostat should be 140.

The boat seems to run good other than it may be running a little rich, which may be caused by the lower temperature. I have noticed that the boat has been hard to start when warm and it also has left a lot of black residue on the transom (through hull exhuast). Can someone please tell me what the correct thermostat should be. I have attached a picture of the thermostat housing.

Enigine: 1997 5.7 LX, Carbed, Thunderbolt 5 ignition (Not sure if it has vortec heads or not, if this makes a difference), Alpha 1 drive
Serial Number:0K167850

 

[problem child]

Re: Wrong Thermostat Installed?

Forgot to add that the engine is raw water cooled...sorry about that.

 

[Fishermark]

Re: Wrong Thermostat Installed?

You want the lower temp thermostat - especially if you boat in salt water.

 

[problem child]

Re: Wrong Thermostat Installed?

The boat has only been in fresh water to my knowledge. I am just concerned that running the boat at a lower temperature than the factory specs may damage the engine. I know that 1997 was a transition year for mercruiser. It seems that all of the "non-vortec" head engines call for a 140 thermostat. The vortec head and efi engines run a 160 thermostat. I have not confimed which heads I have (boat is stored offsite). However, according to the mercrusier manual, the thermostat housing on my boat calls for a 160 thermostat.

I will be performing a complete tune up on the boat in the coming weeks and I want to make sure I am at the optimum temperature before I make any carb adjustments. Hopefully you guys can help me out.