Just got my new 489 installed and ran it on the lake today for the first time. The previous 489 (different block) ran 160 deg, never hotter. This engine runs about 170 deg.

Initial timing is 10 deg at 800 rpm.

All the internals are the same spec as the previous engine.

The only thing I changed was I went with a larger oil cooler. The stock one was 12 in long, new one is 17. Would that account for a 10 deg water temp rise? I'm running a 160 thermostat.

Did you go aftermarket block? The cooler may be larger, but is it as efficient? Is there a restriction, IE smaller inlet or outlet on the cooler? Is your temp sender located in the same spot on the engine?

are you sure you have the cooler lines going the rite way? against the flow..

outlet and inlet are same size as old cooler....temp sender in same location. its not an aftermarket block, just a different block from last time. Line are on there correctly.

Maybe I need to go back to the 140 deg thermostat.

I think I figured it out today. Addl problem I noticed the boat is more difficult to start than it was before, flooding vs starting it on the engine stand before install, no problem. Then today after getting on plane, I heard ticking sound from engine bay. Slowed down, saw exhaust leak from rubber hose which connects riser to elbow (I'm runnning through prop exhaust)...1/8 hole blown right in the side. When I stuck my finger over the hole, the boats idle dipped down about 300 rpm. Before I installed the engine, I noticed 2 rats ran out through the y pipe. I guess they built a nest in my y pipe or something.
That would account for the extra 10-15 degrees.
Luckily I have through hull fittings so I'm going back to thru-hull and capping off the y pipe.