I have a Sunsation that will not get to running temp. 525 efi merc. Rpm 4800 and water temp 150 oil temp 130. Ok we have replaced thermostat. What r the different size restrictor valves and can they be changed for different water temp

Do you have it plugged into a scanner or are you just reading the gauge on the dash?

Reading the gauge. But the Headers are staying ice cold. I read that mercruiser rec to plug lower water restrictors and adding a .406 restrictor valves on both upper restrictor valves. what do u think

Why is 150 a problem? My 575 ran at 150 with the stock 140 tstat all the time? Where are you located?

I believe the stock t-stat is 160, my 525s in my last boat ran about 150. The bulletin for the headers was to increase water flow through them, so they dont get too hot.

Bo is back in the game! Was this running out on the Ohio this past week? I'm guessing the water temp is in the 40s. Even with closed cooling would the cold raw water running through the heat exchanger keep temps in a lower range than say 70 degree water?

Cooler is better than running hot for the headers but ice cold to me would be due to the cold water you're running in.

You're in the water early. I wouldn't restrict anything to bring up the temp. Once you hit LC and temps climb you'll be doing rework to take it back to where it was.

Thought if boat wasn't at operating temperature that the computer maybe cutting back the horsepower .engines running rich also spark plugs are blackI changed out the plugs

RPM is also on the low side. Best to prop then to spin at 5200rpms at WOT.

Get readings from a scanner before making any changes.

Going to take it out this week and hook it to the scanner and even try different prop

Those 525s idle a little rich - if you use premium gas in them, it makes it worse. Had to clean the transom on mine every trip.