Thermostat help needed 5.7 Mercruiser I/O

[yankeeflyer]

Took the boat out this morning for it's first run.Ran great,idles great,everything working except for theThermostat not coming up,it moves a little then drops down and stays down for entire cruise.The hoses were not getting warm and I suspect the thermostat is not opening.I removed the brown wire to one of two sending units and grounded it to make sure the guage was operating..it worked,then I tried the other sending unit,it did not work?I replaced the thermostat with a new one last week but I guess that's not the problem.Any help would be greatly appreciated......Thanks,Rick

 

[mkast]

Re: Thermostat help needed 5.7 Mercruiser I/O

The thermostat is stuck open.

 

[yankeeflyer]

Re: Thermostat help needed 5.7 Mercruiser I/O

I took the thermostat out and tested it in hot water.It opened and closed as it should......what next?

 

[mkast]

Re: Thermostat help needed 5.7 Mercruiser I/O

It may work out of the engine, but if the engine temperature is not rising while the engine is under a load, the thermostat isn't closing.

 

[yankeeflyer]

Re: Thermostat help needed 5.7 Mercruiser I/O

The exhaust water is hot however one exhaust is flowing more water than the other.I removed the thermostat and cleaned the housing and replaced it...still no joy.

 

[yankeeflyer]

Re: Thermostat help needed 5.7 Mercruiser I/O

Well,I give up.I'm going to buy new manifolds and risers with water shutters as the last time they were changed was in 2008 and the boat was constantly in salt water.Also,I did find a piece of a water shutter on the ground.It may not fix my temp guage problem but I'll at least feel better about the engine.