hail mary wrote:
This boat with the 5.8 ford in in is a sob to work on 
What style seating do you have?  If its the U shaped, its very easy to remove the center engine housing (doghouse), once that's out, you have the whole top half of the engine exposed.  As far as removing the T-Stat, its very simple.  2 bolts, 4 hoses.  Make sure you have some shop towels or a small bucket to catch the water, or be quick to point the hoses into the bilge when you remove them.  Also, make sure you have a new T-Stat housing gasket, cause the old one is not gonna be re-usable.  Don't buy an "Official Volvo Penta" gasket, just pick up 2 or 3 from any auto parts store, it will save you a lot of $$$$.  
I say again tho, check your impeller too.