Mercruiser Alpha One Gen II not pumping water

[CaptnKingfisher]

First time working on this outdrive.. it's a friend's boat.. everything was working normal, then one day boat overheats. I come over and replace the impeller and replace gaskets and orings, had the service manual at my side and pretty sure I did most everything correctly, one thing I skimped on.. I didn't have gasket sealer to use on the top of the base gasket. Anyway I noticed the water pump guide tube which has a bend in it looked deformed, wish I'd taken a picture of it but it's shape definitely restricts the flow (inner diameter is significantly smaller almost looks like it was crimped rather than a typical bend like I'd have expected to see). Put everything back together without issue then disconnected the transom hose from the water pump at the thermostat. I poured some soapy water down the hose to lubricate the impeller then I started the engine on muffs. No water came out the transom hose with the engine running. I shut it off, took off the hose and cleaned it but there were no obstructions.

My game plan is to replace the water pump guide tube. I'm thinking I must've damaged it when I was removing the lower? Or somehow it got damaged during operation.. idk what else comes to mind that I should check?

The old impeller was pretty mishapen. I've got in my truck I can post a pic.. but it doesn't seem to be missing any pieces that would be obstructing flow. Any other things I should try or could have messed up? I've changed plenty of impellers on outboards so I felt comfortable with what I did, however when I take it apart to install the guide tube I will double check everything and post pics

 

[nola mike]

The guide tube only guides the water pipe. If that was damaged you might have missed the mark with the copper tube.

 

[Rick Stephens]

When I test an impeller I pull the line from the transom off the thermostat housing and fire up the boat on muffs. You should get a good flow within 20 seconds. If the bilge plug is out, just let it run into the bilge and out.

 

[CaptnKingfisher]

Thanks guys, I'm hopping I just missed the mark as Mike said, I'll go back there this weekend and try again with my new guide tube and double check my install

 

[CaptnKingfisher]

I just wanted to report back, I got a new water pump guide tube and when I dropped the lower to inspect the old one it was bent even worse than it was previously. I believe it wasn't lined up properly and I had positioned the lower unit close to the upper as I could and then tightened the bolts without having the tube aligned, thereby crimping the tube as I tightened the nuts. Installed the new tube and was careful to align everything properly and gently and now it's pumping water strong.

Pictured is the new tube compared to the old

 

[achris]

Yeah, that's what happens when someone forces the gear housing back onto the driveshaft housing, probably pulled it together with the nuts and bolt. These things will go back together with very little effort. If you have to force it, something is out of place, and you'll end up breaking/bending sh*t...

 

[poconojoe]

My guide tube was distorted by heat from a previous owner. Someone must have overheated the engine in the past and that tube got melted. It was all burnt and distorted.

Another thing you might want to check is the exhaust shutters (flappers). They are in to top portion of the exhaust right below the rubber coupling. Their purpose is to help prevent water from flowing back into the engine causing hydro-lock.
They are held in by rubber that can melt from an overheat. The metal flapper parts can fall down and cause a blockage. Sometimes they can even lodge themselves causing the exhaust to rot out.
I found half of one all the way down in my out drive.

 

[Drcoffee]

I just finished my impeller install. First thing I noticed was the plastic guide tube was melted at som point. I used a heat gun to soften the guide and reshape it. The lower unit went back together very easily. I can only assume it lined up with the pump outlet. I will have to wait until spring to test it. Boats been winterized already. Here are pics before and after.

 

[achris]

Looks good. As long as you WATCHED the water tube enter the guide, you'll be fine.

Chris.........