i have a 454 mercruiser and just changed the thermostat and now i cant get the housing to stop leaking, my question is>>>is that plastic sleeve suppose to be flush to the housing when pushed in or is there suppose to be a small lip on it so it secures itself into the hole of the motor block, and than the gasket?????

Thermost...then sleeve (it has an indentation on it so it lines up properly) then the gasket. The lip is raised a little, and when you tighten down the two bolts (draw them up evenly), they put pressure on the thermostat to seal it. You can tighten the bolts pretty tight...just dont CRUSH them. Personally, I always run a bead of sealant on both sides of the gasket.

thanks tinman

Using sealant on the gasket can prevent your temp sending unit from grounding properly, thus your temp gauge may not work.

That MAY be true....but the bolts are digging into the upper housing and the intake....thus making a complete circuit. I've never had a problem with the sender malfunctioning. Maybe I just get Lucky....lol.

thanks for the heads-up, ill try tinmans suggestion and if i loose my temp guage, ill now know to break it down and wipe off the bead of sealent......thanks guys!!!!