Am I running hot or is this normal?

[boat4fun83]

I have a 5.7L 1996 mercruiser. I just want to make sure I'm not running hot. If I am sitting in the water, my temp is around 160. If I cruise at 35-45 for about 10 minutes then it goes up to around 180. After sitting for a couple minutes it's back down to 160. I am assuming this is normal for it to jump like that due to bad air circulation but I wanted to make sure.

 

[a70eliminator]

Re: Am I running hot or is this normal?

Not normal, engine temps shouldn't rise that much even under load, sounds like the impeller, they can go strong for several years without being changed but eventually you'll be overheating.

 

[cr2k]

Re: Am I running hot or is this normal?

Your impeller should be changed every other year. If you use the boat they wear out. If you don't use the boat they get hard and the vanes take a set and are not as efficient.

What you are describing sounds like typical impeller going bad.

 

[boat4fun83]

Re: Am I running hot or is this normal?

I actually just replaced the impeller. Made sure all fins were facing the correct way like the old one. The old one looked fine but i put in a new one anyways. This was the first time I have run it with the new one in. It is surely working b/c it wouldn't cool back off within a few minutes of sitting if it wasn't spinning right?

The exhaust manifolds stayed cool as well.

 

[boat4fun83]

Re: Am I running hot or is this normal?

what temp are the buzzer/alarms set to go off at? I have read alot about boats over heating at idle but mine does not.

Also read the some people have trouble with the exhaust flappers. Would that allow the boat to get hot while driving b/c it's not holding the water in the engine where it should be.

 

[Rocky_Road]

Re: Am I running hot or is this normal?

I actually just replaced the impeller. Made sure all fins were facing the correct way like the old one. The old one looked fine but i put in a new one anyways. This was the first time I have run it with the new one in. It is surely working b/c it wouldn't cool back off within a few minutes of sitting if it wasn't spinning right?

The exhaust manifolds stayed cool as well.

Almost all Mercruiser thermostats are 160 degrees, so yours is obviously opening as designed. If it wasn't you would be getting a lot hotter and very quickly. If it was stuck open, then you would have a hard time ever reaching your operating temperature. I don't see anything wrong with your thermostat....

Keep in mind that any engine will generate more heat when under load, and that is what you are describing. There isn't any danger running at 180 degrees...but I would watch the gauge for anything higher. Your alarm temperature switch is calibrated for over 200 degrees (black band), so you are not even close to what Mercruiser deems an issue.

Happy boating!

 

[boat4fun83]

Re: Am I running hot or is this normal?

That's what I was hoping to hear lol

Should I still check the flutter valves or whatever in the exhaust before I winterize this year. To my knowledge they have not been replaced and it's a 1996

 

[Rocky_Road]

Re: Am I running hot or is this normal?

That's what I was hoping to hear lol

Should I still check the flutter valves or whatever in the exhaust before I winterize this year. To my knowledge they have not been replaced and it's a 1996

From what you have given us, I wouldn't be worried about the exhaust flappers. When they break loose, they usually cause you to have an overheat issue at all speeds. You have said that your exhaust manifolds are relatively remaining cool....

If this were mine, I would make sure that the warning system was operational (buzzer with key "ON", and going off after the engine builds up oil pressure)...watch my gauge(s) when cruising...and just have some fun!

Happy boating!