I have a 1992 5.7L Mercruiser and have noticed that the temp guage is climbing to 200+ when traveling at higher speeds (20 knots and above). If I drop my speed to 10-15 knots the temp goes down to normal (180). I want to change the Thermostat but the book states I have to drain the block and so on. This is above my level of DIY. Can't I just remove the 2 bolts, pop out the old and insert the new?