My 525 EFI runs hotter than 158. It is usually in the 170 range.

I have twin 2004 525 EFI's and both temps run almost identical at just over 150 on the gauges and have always run there. Once they are both warmed up they rarely budge from there except occasionally after coming back to idle after a long run. I had a fuel consumption issue on my port engine and believe it may have been the duty cycle voltage. A buddy of mine found and corrected the problem and now they both burn the same again.

My gauge showed close to 160, but did not show a drop like the scan tool did. On the scan the temp would drop as soon as you hit full thottle and continue to drop down to 144 in a matter of 10 seconds. I talk to a marine mech. and he said that its because of the increase of lake water coming in. I was thinking the stat should keep it closer.

That sounds like the way my 525 behaves. Mine is a 2005 model year.

BTW, the numbers I am stating are coming from my Smartcraft guage. I have a temp guage but it does not have numbers on it, just lines. But, the guage pretty much stays on the same line once the motor warms up.

What kind of water temp are you boating in when these temps drop to 144? What is the size and type of boat this engine is in as boat loadings on the engine can have a big effect on what temp the engine runs at under loads. I have sometimes seen lower temps on bigger power engines in smaller boats.
Its not a huge job to drain the coolant level down and pull off the heat exchanger and check the thermostat itself. Look at the bottom of the thermostat and see what temp unit it is.
If its stuck partially open it can be a problem or opening to soon.
You can put the thermostat in a pan of water, heat the water in the pan and with a good accurate thermometer you can track and observe the thermostat actual opening and closing.

Best Regards,
Ray @ Raylar

Thanks Ray! In my case, it's a stock 525efi in a 30' boat. I can run for miles at 4K + RPMs and my temp will stay around 150. Lately, the air temp is 80+, and the water I'm running in is probably in the 70-80* range. ANY, efi motor I've owned has run around 170*, even when the air and water is cool. This motor is new to me so that's why I'm wondering. I guess I will just replace the t-stat and see what happens. I'm due to replace the coolant anyway.

We are in 80 degree water, temps come down from 158 to 144 in we throttle up. Dave, did you ever check your map readings?

I check those readings tonight when I get home.

Yesterday my temp got up to 167, that's the highest I've seen. It was after about a 15-20 mile run, I came into a creek and came off plane. The water in the creek is much warmer than the main stem of the river.

I'm wondering if my temps are low due to high water pressure. I'm usually running 30-35 PSI.