Impeller

[JBBarry]

I absent mindedly I started my engine on the trailer without water running to the stern drive. It ran for 30 to 45 seconds. Have I ruined the impeller? I did have the engine running previously with the water running. I ran the engine for 20 minutes with water on. It was off for 30 minutes while I changed the oil and filter before I stared it w/o water. The impeller was replaced last summer. It is a 1994 Mercruiser 4.3 with an Alpha One outdrive. Thank you.

 

[Scott Danforth]

I absent mindedly I started my engine on the trailer without water running to the stern drive. It ran for 30 to 45 seconds. Have I ruined the impeller?

yes

 

[JBBarry]

Ugh....

 

[thumpar]

I did it once for less than that and changed the impeller because of it. The impeller looked OK but I would rather be sure than find out 25 miles from the dock.

 

[harringtondav]

Prudence says change it.

The Merc engine manual for impeller health check is to put the boat in the water, disconnect the supply hose from the thermo hsg. Start the engine and set the idle to 1000 rpm. Collect the outflow in a 1 gal min container for 15 seconds and quickly shut off the engine. Depending on your drive's ratio you should collect between 3 and 4 qts. Higher ratio (1.98:1) = less water, lower = more. Ave = 3.3.

We trailered for the first 15 yrs. I always cranked the engine in the parking lot until the engine belched, and shut it off. I didn't want to be one of those clowns clogging a ramp slot with a problem. The cumulative dry run time went way over yours, and I never had or found a bad impeller - generally at seal kit time.

 

[AlabamaNewbie]

I always cranked the engine in the parking lot until the engine belched,

Sorry to hijack the thread.... but I have seen this phrase "engine belch" used several times. What does it mean? We've only ran our engine for a few minutes to confirm it would actually run before starting our project, so I have no clue what an engine belch is.

Thank you

 

[tacx]

Slang for "started".

 

[AlabamaNewbie]

Slang for "started".

Oh. Somehow I was expecting something more. LOL!

 

[JBBarry]

Thank you, all. I think I will just take it to a shop and pay for my stupidity.

 

[Scott Danforth]

it may cost you $300 in labor depending on your shop. videos in the stickies on swapping an impeller.

 

[Oshkosh1]

Not necessarily.

I've run mine accidentally dry for a minute while it was on my lift and the water level had dropped below my intakes. I dropped it into the water further and ran it...I've been running it for two months since and runs cool as ever. Today I pulled the drive to fix my speedo so took a look at the pump and other than a little scorched rubber on the inside the vanes were still perfectly pliable and although I do have a new one...I cleaned up the housing and re-installed it. Like I said...so far as temps go, there was absolutely no difference before or after so don't hit the panic button until you run it and check the temps.

 

[JBBarry]

So the result is I had it replaced for $230.00. Hated to spend the money but now I have peace of mind. I tried to upload a picture of the impeller but it is just not happening. In any event, it is in decent condition and probably did not need to be changed. I think this is because of two factors. First, it was only a year old and a year of light use. Second, I had the motor running just previously with water going through the muffs before running it dry for 45 seconds. Interesting to read everyone opinions and experiences. Thank you for chiming in.

 

[thumpar]

Not necessarily.

I've run mine accidentally dry for a minute while it was on my lift and the water level had dropped below my intakes. I dropped it into the water further and ran it...I've been running it for two months since and runs cool as ever. Today I pulled the drive to fix my speedo so took a look at the pump and other than a little scorched rubber on the inside the vanes were still perfectly pliable and although I do have a new one...I cleaned up the housing and re-installed it. Like I said...so far as temps go, there was absolutely no difference before or after so don't hit the panic button until you run it and check the temps.

The pump will usually cool just fine until it doesn't. Most of the time they don't gradually stop cooling. It all goes at once and you are done. For the $30 I will change it every season before I will be dead on the water again.

 

[achris]

So the result is I had it replaced for $230.00. Hated to spend the money but now I have peace of mind. I tried to upload a picture of the impeller but it is just not happening. In any event, it is in decent condition and probably did not need to be changed. I think this is because of two factors. First, it was only a year old and a year of light use. Second, I had the motor running just previously with water going through the muffs before running it dry for 45 seconds. Interesting to read everyone opinions and experiences. Thank you for chiming in.

Been away and only just seen this...

I know hind-sight is a wonderful thing. That said, it's a Gen II drive, a minute without water after the impeller was wet anyway would not have done any harm.

Chris.......

 

[misery]

One thing you should consider checking out, is your exhaust flaps. With no water they were being cooked with hot exhaust gases for the duration of the run time. It may have burned off some of the rubber and cause them not to seal properly.

 

[Oshkosh1]

One thing you should consider checking out, is your exhaust flaps. With no water they were being cooked with hot exhaust gases for the duration of the run time. It may have burned off some of the rubber and cause them not to seal properly.

I just ran down and picked both of these out of the trash. This is a pic of the impeller and one of the exhaust shutters I pulled out of the boat while the drive is at the shop having a new upper driveshaft oil seal installed. I've run the boat a few times without water for a few seconds here and there and then as mentioned, about a minute or a bit more even having not realized the water level had dropped to below the intake while on my boat lift. The impeller "cup" had a little rubber on it but a few swipes with steel wool and it was new again.

As you can see...both the impeller and shutters look and feel new. The exhaust shutter while a bit brittle, probably has more to do with the fact that it's the original one and is now 26 years old. I pulled to look at them as one of them was rattling due to it losing the small rubber retainers so replaced them with the newer one piece versions.

This is an alpha one gen II drive and as anyone in the future can see...no need to hit the panic button if you've done the same thing. So long as you confirm the water temp is normal after you get water to it...relax. Pull and verify at your next annual maintenance check/winterization routine.

 

[achris]

Those gen II impellers are pretty bomb-proof. I have a friend who's a bit 'forgetful' when it comes to maintenance. I pulled his impeller and it looked pretty good. Then he tells me it's been there for 11 years!

 

[Oshkosh1]

Those gen II impellers are pretty bomb-proof. I have a friend who's a bit 'forgetful' when it comes to maintenance. I pulled his impeller and it looked pretty good. Then he tells me it's been there for 11 years!

The impeller pictured is the original from 1992...Only 300 hours on the boat when I bought it from a friends parents and the impeller has 492.

 

[achris]

The impeller pictured is the original from 1992...Only 300 hours on the boat when I bought it from a friends parents and the impeller has 492.

Ok. You win.