Engine runs hot after sitting- please help!

flypony74

Recruit
Joined
Jun 24, 2010
Messages
2
I recently bought a 2000 Stingray 220LX with a 5.0 Mercruiser, about 300 hours on the well-maintaned engine. The first time we took it out, it ran like a top all day, all of the gauges registered where they should be (temperature ran 180 all day). We stopped for dinner that evening, the boat sat for about an hour or so, and when we got back underway the temperature gauge very quickly started going higher and higher...when it got to about 205 I shut it down and we pulled it out of the water. Figured we'd trashed the impeller, so had that replaced (and based on the condition of the impeller, the dealer felt like that was the problem). Took it out yesterday on a very hot day, put about 2.5 hours on it, and it ran flawlessly. We stopped for about an hour to sunbathe and swim, skied, cruised for a while, and towed a stranded boat in. Watched the temp gauge like a hawk and it stayed right at 180 where it should. Cruised up to the marina for dinner in the evening, parked the boat for about an hour or so, and when we left the marina the temp started spiking like before. We let it sit for a while with the engine compartment open, but when I started it back up, the temp gauge registered even hotter. We ended up getting a tow because I was afraid to drive it.

What in the world is going on? It ran perfectly on a hot day, all day, but after sitting (in the evening, after the outdoor temp had cooled and the sun went down), the temp wants to run high. I've got a call into my dealer but I'm waiting for them to call me back. This is a very nice boat that I've barely had a chance to use so I'm just sick. Any ideas?
 
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carcraze

Petty Officer 2nd Class
Joined
Mar 4, 2010
Messages
141
Re: Engine running hot- please help!

Re: Engine running hot- please help!

Welcome aboard.

A couple thoughts that come to mind to have the thermostat checked if it is locking closed once in a while it will cause it to heat up rapidly. The other item is did the intake get covered by something, weeds, ect not sure if you can trim it all the way up and have a look. Sometimes a shot in reverse can use prop wash to clear weeds off or debris.
 

flypony74

Recruit
Joined
Jun 24, 2010
Messages
2
Re: Engine runs hot after sitting- please help!

Thanks!

Intake appears to be clean. Thought it might be the thermostat but I am a mechanical idiot so I do not know what I am talking about. It is just so strange because it is perfect all day, and ONLY overheats after it has been sitting for an hour or two...and it does it very quickly.

I'm befuddled. All input much appreciated!
 

carcraze

Petty Officer 2nd Class
Joined
Mar 4, 2010
Messages
141
Re: Engine runs hot after sitting- please help!

To me I would start at the thermostat since you replaced the intake pump impeller. If it is locking closed the heat will build rapidly and it is fairly easy to change and be done with it.

I am sure more experianced will chime in as well.
 
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