5.7L 250HP Mercruiser Overheating

[focker1636]

I have a 2001 5.7L 250HP Mercruiser Alpha One Gen II, which has started overheating after running a while on the lake. The boat has never been run in sea water. We typically have a pretty full boat. The engine typically runs @175 degrees, but over the holiday weekend the temperature started rising above 200 and the warning buzzer was triggered after run WOT for a while. This occured several times.

This happened a couple of times last summer. Prior to the summer the boat was serviced and the impeller was changed. The engine has @110 hours and sounds great otherwise. No sputtering or coughing.

Pretty tight on cash. What things should I look for? Thanks.

 

[focker1636]

Re: 5.7L 250HP Mercruiser Overheating

Any ideas on this? We are taking the boat on vacation next week and I was hoping to take a look this week. Thanks!

 

[w317chester]

Re: 5.7L 250HP Mercruiser Overheating

It is probably the seawater pump impeller (commonly wear out as they are usually made of rubber) or the thermostat. both are relatively easy to check and easy and cheap to replace.

 

[PitchFork]

Re: 5.7L 250HP Mercruiser Overheating

Is the overheat occurring at speeds above idle? If it is occurring at only idle after coming off a run then Check the balls in the TStat housing and stretch out the check balls springs. I stretched mine out at the beginning of the season after I was having overheat problems at idle only speeds. We would go through a long No Wake Zone and the temp would rise to 180 and alarm would go off.

http://www.perfprotech.com/store/assembly/STANDARD-COOLING-SYSTEM-(DESIGN-II),1014-220.aspx

 

[focker1636]

Re: 5.7L 250HP Mercruiser Overheating

Thanks for the replies.

The impeller was changed in May when the boat was serviced.

This happens after running the boat for a while (maybe after a couple of hours on the lake) and does not occur at idle speeds. It typically occurs after running WOT for periods. Has also occured after hours of pulling skiers. Also, the times it has happened is when we have a full boat, but then we usually have a pretty full boat.