The location for picking up the water pressure, can it be in the thermostat housing or does it have to come after the thermostat in the intake??

On my Merc 6.2 engines the water pressure sending unit is screwed into the power steering cooler, after the seawater pump, so I assume that's a good location for sending volume info regarding impeller condition. An additional water sensor is in the thermostat housing, they all tied in with the SmartCraft system. I have a hard line plumbed in the themostat housing as a backup, both, Smartcraft and mechanical gauges read the same exact pressures.Location marked in the picture.http://www3.telus.net/spectrasonly/M...06,2%20L%20MPI

That sounds pretty low to me. I get pretty much the same readings from Diacom, Smartcraft, and my mechanical gauge.

Previous boat had a 496HO and at idle it was around 3psi, on the hose, slightly higher when in the water.

Dave, forum member motor's estimated pressure readings at idle is correct. The MPI Merc engines run at a very low [ 600 ] rpm, so there's volume but not much pressure buildup after the seawater pump. Your raise rpm to a 1000 and you'll have instant pressure readings on the gauge. WOT pressures up to 25-30 PSI depending on impeller condition is good. Pressure in the block will be slightly lower [ Bernulli's princpial ] actually because of the thermostat passage restriction but velocity will be increased into the block. 20-25 psi readings on the SmartCraft @WOT, it's all good.Reading pressures with hose on isn't accurate because of the utility pressure way too high, allowing bypass pressure added through the impeller vanes.

I'll take your word for it. I am on a well at home which typically has less pressure than city water. I have a sea strainer too, not sure if that makes a difference in pressure readings.

I think most importantly, I look for consistent readings.