Overheating 7.4 Mercruiser with alarm

[kleake]

I have a 93 2755 with 7.4L. The previous time I was out the boat ran fine until the end of the weekend. I tied up at the dock, put the trailer in at the ramp, fired the boat back up to pull on to the trailer and the alarm started sounding. All guages looked normal, so I went ahead and loaded. At home running on the hose all appeared to be fine so I didn't think too terribly much of it. Put it back in the water on Saturday and a minute after starting it the alarm started going off again. After getting out of the no wake zone all still looked ok, throttled up and about 5 minutes goes by and I notice the temp climbing. It got up to just over 200 when I decided to shut it down. Is there a sensor that detects water flow through the cooling system? I haven't traced the issue yet, but I do have the heat exchanger with antifreeze in the engine. My guess is my new impeller must have gave out, although I haven't checked it out just yet. Any ideas?

 

[Lyle29464]

Re: Overheating 7.4 Mercruiser with alarm

It's easy to burn up the impeller on a trailer-ed boat with a through hull seawater pump. I would start there.

 

[kleake]

Re: Overheating 7.4 Mercruiser with alarm

It's easy to burn up the impeller on a trailer-ed boat with a through hull seawater pump. I would start there.

I agree, but this impeller is only a few months old, and it was running fine all weekend, probably put 2-3hrs of run time on it over that weekend. It failed as i was fixing to put it on the trailer. Is there a sensor that detects water flow? The alarm sounded while the engine was cold and had just fired it up.

 

[Lyle29464]

Re: Overheating 7.4 Mercruiser with alarm

I have picked up an ice bag before. Lots of pumps are built so you can take the hose off and see the impeller?

 

[kleake]

Re: Overheating 7.4 Mercruiser with alarm

Well, two issues at once. 1. the alarm was from the outdrive oil level. I had checked it before the weekend of the first alarm so I didn't think that would be it, but i think there was an air pocket somewhere. Filled it and the alarm went away, so it's good to know that alarm works. The overheat was actually that i was low on antifreeze. I'm not sure where it went, every time I have checked it it was right at the top and plenty green. It took almost a gallon to get it filled again, so i'm going to have to watch this better and see where it was going. I know for a fact it was not overheating when the alarm first went off, but did on the very next trip within 1 mile of the no wake zone so i thought they were related. Both problems solved, but they will need more investigation to make sure it doesn't become a bigger issue. Thanks for the pointers of where to look for the issues.