Scratching my head on running temperature

[Begester]

I've got my boat on the trailer for a week or so before I put it back on the lift again. Every year about this time I notice that my engine runs a bit hotter, it's hot outside and the water temperature is 85 degrees. While it makes sense to me that this is why the engine is running a little warmer, I'd like a little education on why a "good" impeller would do this and if this is normal. While I don't mind changing the impeller, I don't want to change a perfectly good part, even if it is cheap. Was out the other day and had to slow down after about 10 minutes running ~3600rpm as the temp gauge was on the high end of the "normal" range. It was holding, not rising, but nonetheless I slowed down to cool the engine a bit. Lastly, I had the engine out 8 months ago to have the y-pipe changed. After the engine went back in, the manifolds on one side are significantly hotter than the other. It's never overheated, my mechanic said there was no blockage in the manifolds (I confirmed this), but I've also noticed this change. In looking at these forums, this is fairly normal. Nonetheless, it never used to do this. Any education is greatly appreciated. The boat has been running great and I'm looking to keep it this way.

 

[Scott Danforth]

rising temps means lack of flow

since you dont say what the temp actually is, or if this is a 90hp renault motor or a 1650hp Merc racing motor

my first thought is change the impeller. its routine maintenance and should be done every few years.

 

[Begester]

Thanks for the message. It's a 5.7L alpha 1 gen 1 with almost 1700 hours. During "ambient" outside temps in the low 80s and water temps in the low 70s, it runs about 150 degrees...fairly religiously. When it's hot outside in the 90s and 85 degree water temp it's hitting 170 or so. I changed the impeller at the beginning of the season, but I've put about 50 hours on the boat this year.

Still think impeller is the issue?

 

[Scott Danforth]

dont know, not enough information

fresh water or brine? if brine, when were your manifolds and elbows last checked? last time you flushed the engine?

carb or EFI?

if carb, your running warm as the thermostat should be 140

if EFI, your running cool as the thermostat should be 160

when was the last time your PS cooler was backflushed and cleaned?

 

[Searay205]

Pretty sure you have 160 F thermostat. Your temps mimic mine on the cold water but when water temp is 85F i hit 160 or 165 if driving very hard. 170F your fine. especially if fresh water. I have an impeller sitting in housing in my garage for 12 years looks good, sure it has a set but zero cracks. Elastomers have come along way even mercruiser says to check not replace. You will gain nothing with a new impeller, mine is 3 years old. I got tired of replacing perfectly good impellers. I had one go 8 years on another boat, I replaced just because, blah. All saltwater

By the way my temp gauge doesn't have numbers but just as it hits bottom of high zone is 160F, I get my temp from my Rinda tool. Manifolds usually run 144 and 130, sometime closer in temp.

 

[Begester]

Thanks Scott and searay205.

Scott - saltwater, with closed cooling. Carb. Manifolds and elbows checked back in December when engine was out, no issue. Since then I've put about 50 hours on the motor. I flush it every time. Good question on the power steering pump, it's been a long time... probably 10 years or so. Fluid looks okay and it's not leaking. Would that have anything to do with cooling though?