I replaced the impeller on SBC Volvo Penta and it seems like the crank mounted raw water pump is having issues priming off the garden hose with the new impeller. If I squeeze the ear muffs really tightly to the drive it primes and pumps water thru the motor and then is OK. Or if I attach hose to the "T" I have in the inlet side so I can flush boat while in the water . But if I shut motor off, remove muffs to allow the drive to drain and try to flush again it has hard time priming unless I squeeze the muffs by hand to the drive. I triple checked the hoses (inlet and outlet) are right orientation and they are. Any thoughts?
The pump has some scoring to the housing at the thrust surfaces and I am waiting to hear fro Jamie at Lakeside for the price of a complete pump. I don't think that is it though because I replaced impeller simply as maintenance deal and was fine prior to that.

I had that same problem before. Under no condition could I get the water to go through the drive by way of the muffs.. Thought it was an obstruction in the drive or hoses, so pulled the drive off. No blockage anywhere. For chits and grins, I hooked the muffs to the drive with it sitting on the stand. Water would still not flow throught the drive at full water pressure, and that's just a 1- 1/2' verticle path Tried a spare set of muffs, no problem. Craziest thing I ever ran across. Wouldn't have believed it if it didn't happen to me.

My thoughts are......I think over time the muffs get hard, less pliable, and don't make a perfect seal against the drive housing, so it's just sucking air. That would explain why it works when you force teh muffs tight against the drive.

The muffs leak some, always have and that is less than ideal for sure. I have a second set around somewhere and when the rain quits I will try that. I thought about dumping boat in water to see what it does. The second set of muffs is easier.

All muffs will leak...that is the excess water will blow past them. What you may have is water leaking past the areas where the muffs are leaving a small air gap. Post your results from the 2nd set. Be curious to see if that is the problem.

It is the correct impeller , isn't it? Did you compare diameter and width?
I changed to Volvo style crank pumps on mine 4 years ago for ease of service compared to Mercs and have never had a problem.

I tried second set of muffs, same issue. I will pull it back apart tonight and compare the impeller to old one. I am 99.999% sure same part number as in the past though so unless it was boxed incorrectly it is right one. Just suks the new pump is 300 bills. :-( I wish they used stainless wear plates

Sure you didn't reverse the hoses on re-installation? Had a friend do this before ... easy to do.

Why use the earmuffs if you have a T-inline fitting? I HATE earmuffs for flushing.

Yea, i though about the reversed hoses too. I have checked them couple times. And I am 100% sure they are right. VP uses a slightly larger hose on one side too so that helps. Don,
I thought of that too. (the flush "T" leak.) I double checked it all and I think it is air tight.

I will call my local VP dealer to see what they want for the pump, Jaime at Lakeside gave me cost of $240. I would prefer to support OSO people (and I think that is good price) , but I really want to use boat Friday (have day off) so shipping might be a thing . Since the pump has scoring on both thrust surfaces I suppose it is not going to last forever anyhow. I just hate throwing parts at something when not 100% sure. The fact the issue arrived when I replaced impeller bugs me. (I am a "need to know root cause" kinda guy) .

As far as using "T" to flush , I agree, it is easier in some ways. I guess I didn't say all the info, the last time boat was in the water if I ran it really hard the temperature would creep up. Since it was over due for impeller I figured that was reason. Now that I have the priming issue, I am not sure.

Do you run in a lot of shallow water? Perhaps you need to flush the entire motor and all oil/fuel coolers & heat exchangers (if equipped) manually.

You could have sediment in the bottom of your cooling system which is affecting flow and/or the thermostat.

This probably isn't your priming problem, but could be your creeping temp issue.