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Old 08-12-2019, 11:10 AM
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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.

Last edited by imartin; 08-13-2019 at 12:43 PM.
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Old 08-13-2019, 11:38 AM
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Originally Posted by imartin View Post
2007, twin 525efis. 162hours, impeller change on both 20 hours ago, Apr 2017. Recent issue last two times out, port side temp 142-152 or so, but stbd now starting to run about 6-7 degrees warmer up to 158-160. Being closed cooled, my ( ovice) 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...
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Old 08-13-2019, 11:49 AM
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If you last changed impellers in April of 2017 like mentioned above, I would do yourself a favor and change them. Sitting that long, drying out, etc kills impellers. I always change mine at the start of the season whether I need it or not. More often, I’ve found cracking in the rubber impeller or some other detriment.
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Old 08-13-2019, 01:00 PM
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My 525 efis run 159 starboard and 152 port at cruise. Water pressures are with in a few psi, never have had a problem.
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Old 08-13-2019, 01:09 PM
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Originally Posted by dcb View Post
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?
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Old 08-13-2019, 01:30 PM
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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
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Old 08-13-2019, 02:25 PM
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You have nothing to worry about. Are these readings from smartcraft? People always freak out when everything isn’t the exact same but it hardly ever is. A 6 degree difference usually doesn’t even show on analog gauges. Run it this year and put new impellers in next spring. I replace mine every year and use the old ones as backups
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Old 08-13-2019, 02:41 PM
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Originally Posted by jbraun2828 View Post
You have nothing to worry about. Are these readings from smartcraft? People always freak out when everything isnít the exact same but it hardly ever is. A 6 degree difference usually doesnít even show on analog gauges. Run it this year and put new impellers in next spring. I replace mine every year and use the old ones as backups
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.
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Old 08-13-2019, 09:09 PM
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Originally Posted by imartin View Post
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.
. The engine oil cooler is the first to plug up and cause blockage. It is located at the rear, up high on the engine. Working from the front of the engine, itís only one center bolt to remove the left side plate on the oil cooler and clean out old impeller fins or other debris. I used needle nose pliers. I also back flushed my system. Itís very hard to see. Use a mirror or cell phone to see better. You will need a new gasket.
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Old 08-13-2019, 09:59 PM
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Originally Posted by woody81 View Post

. The engine oil cooler is the first to plug up and cause blockage. It is located at the rear, up high on the engine. Working from the front of the engine, itís only one center bolt to remove the left side plate on the oil cooler and clean out old impeller fins or other debris. I used needle nose pliers. I also back flushed my system. Itís very hard to see. Use a mirror or cell phone to see better. You will need a new gasket.
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....
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