2007, twin 525efis. 162hours, impeller change on both 20 hours ago, Apr 2017. Recent issue last two times out, port side temp 148-152 or so, but stbd now starting to run about 6-7 degrees warmer up to 158-160. Being closed cooled, my (novice) question is does the impeller significantly impact the engine temp? Manual says check for obstructions in pick up, I think coolant was changed in 2014 at 100hr service. Should I be concerned see 158-160 temp?

Of note, TX temps up to 100 now so water is warmer too. Other thoughts or comments? Thx in advance.

So, reached out to Merc Racing with my question. They were very helpful, let me know that a 7 degree diff in engines is not concerning. Also, while wide open thermostat is at 160 degrees, guardian mode/alarms etc dont kick in on the 525efi until 200 degrees. If the heat exchanger is getting a tad less water/pressure maybe from a lazy impeller or blockage, one will see a slight temp creep. Will check my water PSI numbers next time out to see if in range and watch things. Maybe new impeller in the not too distant future, cheap insurance...

My 525 efis run 159 starboard and 152 port at cruise. Water pressures are with in a few psi, never have had a problem.

yes, that sounds exactly like my situation. When impellers last changed on yours? How many hours on your 525s?

Just sitting over the course of a winter the impellers will gain a memory/ not straighten the fins out to maintain full pressure/sidewall contact and no longer pump the same water flow as new (Impeller spins in the casing as an eccentric not a round bore)..

Impellers are cheap vs. the damage from an overheat/ down time involved

Good point, YES these readings are on SmartCraft. Analog does show slight diff, but I am looking at the digital. Im just nervous Nelly I suppose, lol. Thats what my plan was, get a few more runs out of her this year, get new impellers on order, replace in Spring. All freshwater its entire life, limestone bottom lake, no beaching or muddy silt, easy hours, and change the housing and all on changes. The guy at MercRacing said sounds like very gentle use, not abusing anything, no big worries. Thanks guys.

new impellers ordered...I doubt any debris pick up given the sole lake I boat on and conditions as described, but will know once I open up the impeller housing....Next time out, will check for 2psi water pressure at idle, 11 min (15-20 ideally) at 4K RPM....