Running hot, SMOKED NEW IMPELLER blockage in outdrive?

88 Four Winns , 4.3 Chevy , Cobra outdrive , low hours.
Sorry, this will be long read but didn't want to miss anything that might be important.
Thanks in advance!
Bought boat without upper half of outdrive. Previous owner changed fluid, filled from top, locked it up.
Bought used upper half and had strange problem. There was a rubber expansion plug I had to remove from the upper half that blocked water flow. Removed freeze style plug from side of outdrive (behind cobra logo) then replaced freeze (expansion) plug.

Boat ran cool on hose with muffs. First time on lake it got hot under power. Shut it down to idle in neutral figuring would cool off faster if I kept the water flowing. Stayed hot. Bumped idle up from 800 or so (what ever low idle was) to around 1300 and it cooled down.
There was a hairline crack in the plastic impeller housing so I ordered kit with housing, cage, impeller, gaskets. Winterized for season.

Installed new impeller kit last week and fired it up on the muffs. Great so far.
With a little more reading decided to check a few more possibilities for flow blockage. Also, new T-stat went in last fall. Pulled water into stat housing and started with muffs on, water flowing. Pulled impeller housing and stuck garden hose in inlet house that connects to stat and water flowed out the outdrive at the impeller housing area. Re-installed the impeller, put muffs back on and fired it up. Exhaust risers got too hot to touch so I knew something was wrong. My boy said "that supposed to be smoking?"
Shut it down and found new plastic impeller housing melted.

No water coming up to the impeller from the muffs (?)
Pulled impeller housing (with glove on). Put garden hose down the opening that water comes up from the intake openings in the lower and water flowed out. Put muffs back on and water did Not flow up to impeller area. Goes one direction but not the other. Well, doesn't go the way I need it to go.

What is in there that could be blocking the flow? Why was it fine a few days ago? I was going to put it in the lake today to see if it got hot again under power. Was thinking all kinds of things like blockage in ps cooler, blocked exhaust manifolds/risers, etc.
Maybe my only problem (looks like possibly intermittent) is a blockage in my lower unit. Possibly had nothing to do with being under power but just happened that time last fall and not on the muffs last fall just like it was fine a week ago but not today.

Didn't want to drain lower and pull yet. Hoped for some ideas on what to look for. Common?

Re: Running hot, SMOKED NEW IMPELLER blockage in outdrive?

Not sure that was clear at the end.

With impeller housing off there is two holes for water, one goes up to engine the other comes up from water pick up screens near bottom of lower unit. If I put water in (down) the hole where it would come in (from lake or muffs) it freely pours out the bottom.

Trying to push water up to impeller area from water inlets with muffs on does not produce any flow.

Something not hooked up in lower unit? Disconnected? Broke?

Hope it is clear as mud now. Thanks again.

Re: Running hot, SMOKED NEW IMPELLER blockage in outdrive?

There are 2 small holes on the starboard side right near where the suction cups will be, water should be peeing from both those little holes without engine even running, if it's not then you have blockage before the pump. If water is present there then I'm going to just guess that when you assembled the lower to the upper the water tube did not make the connection.

Re: Running hot, SMOKED NEW IMPELLER blockage in outdrive?

I have no such holes. I think the lower half of the outdrive may be aftermarket, prior to my owning it so not sure. It is light grey not dark grey like the upper half and the gymbal housing.

I thought I'd wait for help but couldn't wait, naturally.

I pulled the outdrive and seperated the upper from the lower. Good water flow thru both parts. Pulled feed hose of t-stat housing again and fed water both ways thru it just fine. No blockage anywhere. Seems fine.

I'm also now thinking that , like you said, the water tube didn't make the connection when I installed the upper and lower together last fall.
One big thing bugs me however... I ran it last week on the muffs and it didn't get hot then.

Should I check for water flow (water tube connected right) before hanging the outdrive back on the boat after I mate the upper to the lower? Will be easy enough with the muffs on and the impeller housing still off.

Strange. I should stick to working on cars.

Re: Running hot, SMOKED NEW IMPELLER blockage in outdrive?

House water hose pressure can be misleading. Might have been forcing the flow and disguising the problem.

Re: Running hot, SMOKED NEW IMPELLER blockage in outdrive?

Seems intermittent like something blocks flow only sometimes. I got good water flow thru both halves while they were apart. Put them back together and checked again and had good flow.
Put outdrive back on boat and hooked up muffs and left impeller and housing off to witness water flow.
Blocked again!
Put hose up to hole where impeller pulls it up/in and water freely flowed out the bottom at the intake grates.
Put muffs back on bottom and now water flows nicely
out the top...
Then it stopped flowing again then after shooting it backwards from the top it worked fine again from the bottom with the muffs on.

I removed the plastic intake grates just in case they were trapping any debris.
Left the muffs on with water flowing to try to flush out anything. I'll give it a while like that.

I don't think it is related to house water pressure in the hose because the blockage comes and goes. Last week on the hose it never got hot today it melted impeller.

Still stumped

Re: Running hot, SMOKED NEW IMPELLER blockage in outdrive?

Do the muffs fit real tight?

Re: Running hot, SMOKED NEW IMPELLER blockage in outdrive?

Idlespeedonly said:

Do the muffs fit real tight?

Click to expand...

They are pretty tight, new pair. I made em even tighter by pounding on the metal bracket and closing the gap.
They still leak quite a bit because of the shape of the outdrive.

With the impeller and its housing still off to watch water flow.. It isn't a lot. Lots being forced around three muffs. If I hold them even tighter then more is forced out the top.

I can't imagine what kind of poltergeist I have in there. Going to fill with gear oil tomorrow and hope it runs cool in the driveway. Maybe even get the chance to drop it in the lake tomorrow night.

Still kind of apprehensive about that.