Theoretical question about overheating

[lakelover]

It's time to routinely change my impeller on a 2003 Mercury 20. Thinking about it, I got wondering about this. If the impeller failed, is there any kind of built-in protection to shut the engine down before major damage is done, or do they just fry? Maybe a complete sudden failure is pretty uncommon unless the impeller is really old and it would usually fail gradually and give some sign?<br /><br />It would seem that in modern engines there would be some sort of protection from this.

 

[steelespike]

Re: Theoretical question about overheating

Larger motors have a warning system and some even have a slow down feature and of course alarms.My guess is smaller motors don't have any warning/shutdown etc.Vigilance is the key word.<br /> My 88 Evinrude 50 just got a new impeller this spring for the first time.I sure don't reccomend going 17 years but makes you wonder what the actual life of an impeller is.

 

[dakk1]

Re: Theoretical question about overheating

It seems that the basic water pump design hasn't changed in a long time. Maybe it's just one of those things that can't be improved. Or maybe there is some other reason.

 

[Paul Moir]

Re: Theoretical question about overheating

If you suddenly loose the impeller/coolant for some reason (picking up a bag, etc) you'll notice two things on a small engine. 1) the rpms suddenly pick up a bit and 2) the exhaust has a real "hollow" sound to it since there's no water in it. <br />Assuming you miss the tell-tale disappearing, of course.

 

[lakelover]

Re: Theoretical question about overheating

I'm wondering about doing this service myself. Only problem is I've never done it before and the repair manuals I've seen available only go up to the 2000 model year. I've done a little ("very little") work on an outboard such as replacing cylinder head, thermostat and rebuilding a carb etc.<br /><br />Any thoughts/recommendations?

 

[swist]

Re: Theoretical question about overheating

The life of an impeller is pretty long if all that it impels is water - but that's rarely the case - all you gotta do is draw a little mud/sand and the impeller is now an orbital sander. Also spinning even for a few seconds with NO water (oops I forgot I left the motor up when I started) will do a number on it and its mating canister. Sucking a plastic bag into the intake will do the same thing.<br /><br />Regular changing is done under the assumption that everyone draws in some crap now and again, or has some period of no water flow.

 

[mrloring]

Re: Theoretical question about overheating

landlover<br />Impeller replacement is a fairly simple process, although I would recommend getting an OEM manual as they are far superior to the aftermarket manuals. Most outboards do not change very much from year to year, so it is possible(not familiar with mercs) that an older manual will work. I would try to borrow one (library) or at least get one that you can look at and see if the outboard looks similar. It might be close enough that it will work.

 

[timmathis]

Re: Theoretical question about overheating

Lakelover ,I think you can go to Mercury.com and get the information you will need to change it yourself. If that is not the site, search for Mercury online manual. Tim