Might as well, that`s the only thing that`s not new.
They are not reversed.

I had 2 days boating last weekend and flushed it on the hose in the driveway when I got home. No issues.
It sat for the week and Saturday morning I start it on the hose and zero water flow.

To be clear, when it screws up, it is from no water flow, it seems like it loses prime and won`t pick up water from the drive to the pump.
When I start it on the hose, I go to the stern on look over to the exhaust pipes to check for water flow, if there is none I shut down right away.
It does not pick up water flow and lose it, it either is some or none.
It doesn`t run long enough to over heat.

Is the belt tight running the pump..........

yipper, double checked that to. Tensioner bearing ok as well.

I was boating yesterday and got home late so I didn`t flush it.
I will after tonight and see what happens, I will double check everything and see if I can observe any hose collapsing.

How do the impellers look when you've replaced them?

Do you know the issue is at the sea water pump or could there be blockage down the line?

An easy thing to check is to pull the lower hose from the oil cooler and check for old impeller pieces or other crap. Grab a pick/hook set from Harbor Freight - http://www.harborfreight.com/Pick-an...-Pc-69592.html (or equivalent) as that makes it a lot easier to loosen the hose - use care and some common sense.

If you are going to replace this hose, go ahead and install a Fresh Water Flush point with a "Tee" in this hose, so you can hook your garden hose directly in front of the SWP. This way you can throw your muffs in the garbage.

This is a rudimentary picture I grabbed off of Google, but you get the idea.

Also, have you replaced the plastic housing and impeller in sets? I've heard the housing can get scored/beat up and impact the water flow....

The way I see it, this can only be (3) things causing this:

* No water from the drive to the pump (backflush the inlet hose from the sea water pump thru the drive as a quick check)

* Seawater pump not functioning (not sure this is a good idea but remove the hose at the first cooler, point it somewhere safe, hook up the hose and run it at low rpm or maybe even just feel for water at the first hose)

* Blockage (remove hoses and backflush from the thermostat housing back to the sea water pump - again, pay close attention to the inlet side of the oil cooler)

There is lots of good information if you search for overheating, backflush, sea water pump, etc....

Hope you get to the bottom of it, I would have been fed up a long time ago.

Next time you are at the launch and it won't pump water, try purging the air out of the intake hose before calling it a day.

Loosen the intake hose at the water pump, let the air purge out then re-tighten the hose clamp. The way your hose is routed from the pump to the transom assembly may be allowing it to siphon out on your way home on the trailer, then you have an air pocket.

The impellers are trashed when I pull it apart, most if not all the vanes broken.

I could be wrong but I think if there was a blockage on the outlet hose or cooler, I would have the temps go up and maybe only a little of bit water out of the exhaust tips, but you would not expect to see complete blockage and no water out the tips.

I have pulled both hoses off and checked for debris and checked the inlet on the cooler as well.

And, as soon as I change the impeller, as is well.

That is a good idea and I will likely do that.
But that is not going to help when the boat is in the water and still won`t pick up water flow

That is another good suggestion, but by the time you know there is no water flow, the impeller is toast.

I could undo the hose and burp it before starting it though. That might help.