Shouldn't my impeller be toast?

[JGJR]

Long time reader, first post. 2006 Sea Ray 185 Sport, 4.3l Mercruiser, Alpha one gen 2.

So I did something really stupid, put the muffs on to flush the saltwater after having the boat out. Turned water on, started her up. I was tinkering with the wiring behind the dash, had the alarm unplugged to get it out of the way while it was running. After about 4 or 5 minutes I turned around and thought "Man, that's a lot of exhaust smoke behind me." Got down and noticed the cutoff valve on the end of the hose was OFF. Immediately turned it on, climbed back in and flipped dash up, temp gauge was about 205. Left boat running ( probably a mistake ) and waited until temp came back down to normal, about 170. Water was coming out the back like usual. Shut it down, spent about 15 minutes cussing myself and then set about going to the parts store to get an impeller rebuild kit, planning on returning for flapper and hoses if I need them and wondering how much I could get for a 13 year old dinged up boat with a burned out motor.
Last weekend I pulled the outdrive and split it, opened up pump housing expecting to see melted rubber. What I found was an impeller that looks about the same as it did when I installed it in January. (No luck posting photo.) Slight bluing on housing but that's it. Replaced it anyway, checking other things next.
My questuons are, how is it possible that the impeller didn't destroy itself running that long dry? And what other issues should i expect? Engine didn't cut off or sound different, and ran fine on muffs with new pump.Any opinions are much appreciated.

 

[achris]

Hello JGJR, and :welcome: to iboats....

Those long vane impellers are pretty good at absorbing abuse, it doesn't surprise me it wasn't damaged.

What I would suggest you do is run up the engine to temperatue again (with the water on this time ), then do a compression check. With the water off for that long, you have probably cooked the exhaust shutters, but that's not a difficult fix... Other than that, take it out and see how else it performs. I wouldn't expect too many problems...

Chris..........
Oh, you can't attach photos until you have 3 posts. What you can do before you have 3 posts if you want to add photos, is to upload them to a photo sharing site and add the link in your post. That will show the photos like they were attached.

 

[Bondo]

Slight bluing on housing but that's it.

Ayuh,..... Welcome Aboard,..... Did you change the housing, 'n all,..??

As Chris says, the Gen.II impellers are much more forgivin' than the older Alpha 1 impellers,.....

 

[JGJR]

Thanks for the replies and welcome. Yes, changed housing, wear plate, gaskets and seals, as well as the seal carrier, which had some wear on the top and looked original. This is my first boat and I have no maintenance records from the previous owner (s) other than the block, manifolds and risers were replaced in 2018 as it wasn't drained the previous winter and it got frozen. The price was right, so I figured if all of that stuff was new I at least have a good foundation and I can figure out the rest. It's damned interesting. And I appreciate all the wisdom you two (achris and bondo) impart on this forum. Been lurking here for a while and it's helped tremendously.

 

[Rick Stephens]

Being as how you were at idle the two risky things were burning up some of the rubber and then introducing cold water to a hot engine. As already well stated, shutters need a look at along with the exhaust rubber, and then test run it to see what you have. I really like that you are diving in and doing all the maintenance now since there is no way to know what was skipped in the past. Best of luck on the testing!

Rick

 

[JGJR]

So I'm looking at the starboard exhaust flapper. It has an undamaged rubber jacket, feels solid and attached but, it is hanging slightly open, although I feel sure if water cane rushing up the exhaust pipe it would slam closed and seal the opening. Is this the normal condition? Should the spring be strong enough to keep it against the walls of the y pipe until the exiting exhaust flow pushes it open? Or should it have a natural gap in the "at rest" position?

 

[rock doc]

Usually one side runs hotter than the other. I would check the side runs hotter. There is a possibility you scorched the rise gasket too. If it leaks you will get water intrusion into the oil.

 

[JGJR]

Inspected port and starboard flappers, both sides in good shape. Compression test results:
#1 175 psi #2 182 psi
#3 180 psi. #4 180 psi
#5 178 psi #6 180 psi

I'm thinking I dodged a bullet here. If I end up with water in the oil I'll check the riser gasket, given everything else I'm willing to risk it. Going out tomorrow with the rest of the idiots to see how she does.

 

[Rick Stephens]

Good luck!