Raw water pump issues

[henry.blanchette]

Hi all,

A month ago I ran my A4 with the raw water intake closed and overheated the engine and fried the impeller. I replaced the impeller and still overheated. I assumed it was a piece (only two small ones unaccounted for) of the old impeller clogging up the heat exchanger. However after more thorough investigation, it seems I haven't had an opportunity to have that problem yet. I am not getting water to the heat exchanger. I am getting water in through the thru hull fine. when I take off the inline strainer and open the thru hull water comes in. there is no blockage in the hose from the strainer to the water pump.

I disconnected the out flow hose to see if water was coming out of the pump itself.
I filled the intake hose with water (holding the disconnected end in the air) from the end i disconnected from the strainer and ran the engine. water at first dribbled out but then stopped with water still remaining in the intake hose. The impeller looks fine when I take the back plate off and take a look. the brass fitting on the outflow side is clear. The belt is in good shape and the drive seems to be turning.

I don't know what else to check. any thoughts on what could be going wrong would be greatly appreciated. Thank you!

[ndutton]

The first thing I would do is measure the thickness of the new impeller and the depth of the impeller cavity in the pump. Make sure the impeller is slightly larger than the cavity depth. A tape measure isn't accurate enough, must use a caliper.

[Wrsteinesq]

Is it possible that a piece of the fried impeller did in fact make it to the heat exchanger? Clogging it, such that now, you have an airlock between the heat exchanger and the pump?

[Wrsteinesq]

Sorry; I missed the part about disconnecting the discharge/outlet hose from the pump. So, what I’m hearing is: No impediment between the seacock, i.e. the seawater intake, and the strainer. Water’s getting thru the strainer unimpeded. But it’s not flowing thru the pump, which appears to be turning as it should. Now, I’m assuming that all this is below the waterline, i.e. if you removed the intake hose from the pump, but held it at the same elevation, water would naturally flow, and eventually sink you. So if it’s not coming out the pump outlet, then either there’s a problem with the pump, OR there’s some impediment, maybe an airlock, between the strainer and the pump. What am I missing?

[henry.blanchette]

no worries, I appreciate the follow up. A picture is worth a thousand words, but oh well. water flows in when I disconnect the strainer which is just about the seacock. I think the water pump must be a tad higher. if I disconnect the intake hose from the pump water does not start to pour out of the hose. However to test if it was a water intake issue I disconnected the intake hose from the strainer side, still connected to the pump, flipped it up so i could fill it with water from the sink and know i was running water with the help of gravity to the pump, then ran the engine. at first some water drippled a bit, then stopped, leaving water in the hose.

all tests were done with the outflow hose disconnected, ruling out any issue with downstream occlusions.

[henry.blanchette]

also, thank you neil, I will double check the dimensions. I cross referenced things when I bought it, but I could have gotten it wrong i suppose. to the eye it looks right