nsformula

that may be doable.

sutphen 30

hose is pressure to the pump,,now try that in a big tub and see if it will suck the water up.

nsformula

I get that, but the issue is inconsistency.
Burned up the impeller Saturday morning parked in the same place. Boat had sat for 2 weeks.
Installed new impeller, changed nothing else, and it has worked perfect since.
The process of changing the impeller would release an air lock, I believe.

I think time to drain back is the issue, and or the movement and incline to allow it to drain.

I have been thru all the hose stuff numerous times and not found a fault.

A strainer or vent on the water pump inlet hose sounds like a fix to me.

dunnitagain

An Airlock in a Stock mercruiser setup is very unlikely. Do you have any friends that do Automotive Evap work ? If yes they have a Smoke Machine to check for leaks .
Hook it to the pump Inlet Hose , tape the water pickups closed on the drive , then see if smoke comes out any connections, Especially where the neck bolts to the back of the transom plate.
. You have an air leak , or kinked hose .
I would pull the drive , replace the bell housing ( or Helmet ) hose to transom plate , and the transom to pump hose in the bilge . Then I would split them with a razor blade .
You might get a surprise ! Or you could keep on with the Air Lock Theory and keep replacing Impellers on the water.

BUP

iTrader: (9)

Are you just throwing impellers in and NO NEW HOUSINGS and the other new parts that comes with the kit ? You need to do the whole kit. You should the black plastic housing impeller set up.

Also how hard are you cranking down the bolts at the black plastic housing ??? They require a 3 pass to 10 lbs ft only in a star pattern of tightness. Overtightening the bolts cracks the housing and will not pump water.

Next who's impeller and or kit are you using ???? How old are these - new off the shelf or been laying around for years ???

Next your inlet hose engine compartment side is too long and kinked ??? check that out as a water restriction to the impeller.

Bravo does it has have duel water pick up - if so when running on the hose you need to block off the water inlets of the front bullet.

If you are installing the whole kit for the impelling - housing - wear plate and one small o ring and one larger one, impeller are you using all the new parts in the kit ??? Also again who's kit is it ?? You need to do the whole kit its about 100 bucks.

Did you hook up your hoses back side of the impeller housing wrong ?

nsformula

I do have access to a smoke machine and am familiar with how they work. Good suggestion.

Again, I get that, and may end up pulling the drive.

But, no one has explained why it does not f-up every time.

And, more importantly, why a new impeller fixes it every time.
With the new drive or the old drive.

Remember, it only burns up on the first startup, not after it has been running.
If it starts and pumps water it keeps on pumping water.

nsformula

Sometimes I change the impellers only, if the housing has not been scored, sometimes I do the whole kit, always Merc parts.
Either way, it always picks up water and runs perfect until the next time the boat is laid up.
The inlet hose to the pump looks like oe parts, is wire reinforced and I have removed it more than once to push something thru and check for obstructions and found nothing.
The hoses are not reversed on the impeller housing.

I believe my new drive [ installed end of last season] is dual pick up, has holes in front of the bullet. My old drive did not.
I have had the same impeller issue with both drives.

My thought process still goes back to why does a new impeller or full kit fix it every time.
Why does it work fine for the weekend, once it picks up water.
Why does it only fail after towing or sitting on the trailer for awhile.
Why the same issue with 2 drives/transoms.

I sincerely appreciate all the help and feedback everyone has offered and I know it seems like I am refuting what people are suggesting.
But I have already done most of what has been suggested.

SB

iTrader: (1)

Other than not running it on the trailer between each replacement.

What have you got to lose ? Don't run it on the trailer and see how long it lasts.

Questofpower

Are you blocking off the nose cone pickups when on the hose with the new drive. I know you are saying that you are having the same same problem with the old drive as the new one. However, even though the result is the same in a burned up impeller, it could have been being caused by two differnt things. Air introduced at the transome assembly or at the nose cone will equal a burned up pump at some ponit in either case.

I would take SB's advice and stop running it on the hose until you install a t-flush kit. Your on water failures I think are just chance after the impeller has been damaged from running on the hose.

nsformula

I got into the habit of running on the trailer as I had a few incidents at the launch, dead batteries, hose leaks etc.

I put a battery charger-conditioner on this boat and it`s plugged into 110 while parked, so the batteries should not be an issue.

Maybe I don`t need to start it on the hose, pre-launch..
But again, it has taken a crap on first start up in the water too.
But worth a try, not much to lose at this point.