water pump problems

[dcsavitzky]

Hello All,

I'm looking for some confirmation before I pull my rebuilt water pump out. I have an early A-4, raw water cooled, with an Indigo Thermostat plumbed into the manifold output. My water pump output has been anemic for a few years and when there was water coming out of the weep holes in the pump body I got the MM rebuild kit. The rebuild went relatively smoothly and the reinstall looked good. The block was full from the 5 gallon bucket on the cabin top and then I switched back to the through-hull input. I was able to get some water out the exhaust but it pooped out.

I have blown out the pump inlet hose, through the strainer and out the through-hull. With the back plate off, and the through-hull open, water flows freely out of the pump. I disconnected the bypass (from the pump output to the thermostat) and put a hose on it, then clamped the output to the block. Cranking over the engine, nothing emerges. I rechecked the impeller, again, and it is fine. I am ready to pull the pump and send it to MM to confirm that it actually works (hoping they do that). Before I do that, I am soliciting advice - what have I missed? Is there something else I should do before blaming the pump rebuild and finding a way to test it out of the boat?

Thanks in advance,

David
Providence, RI
T-27 "Sleekit"

[JOHN COOKSON]

Did the rebuild include a new impeller? If not I would try a new impeller before going any further. There have been problems with impellers in the past. As I recall there was a batch that were a few thousandths thinner and didn't work so grand. Maybe you have one of these impellers. When I get some more time I'll try to do a bit of research.

TRUE GRIT

[dcsavitzky]

Thanks. The impeller was the new one that came with the rebuild kit.

[indigo]

David, I suspect your problem may be as simple as clamping off the re-circulation loop on your Indigo thermostat. It is the hose that comes off the bottom of the thermostat housing. If your cooling system is not completely full of water, the recirculation loop causes any air in the system to just go round and round and the pump will not pull in any new raw water. By clamping it off for a short time you will purge the air out of the system. Once you get some water coming out of the exhaust, slowly un-clamp the re-circ hose and you should be all set. Remember that there will not be a lot of flow out the exhaust until the thermostat opens.

Tom

[zellerj]

There has been an issue with impellers being too thin to create the suction needed for the pump to work. This was attributed to a bad batch of impellers. The impeller has to have a tight fit with the backing plate. If there is too much of a gap the pump will not work.

http://www.moyermarineforum.com/forums/showthread.php?t=7118&highlight=impeller+thin

[ndutton]

After you follow the advice provided (Indigo should know their system best), if the symptom persists I suspect pump cavity wear. For the pump to function to spec the faces of the impeller must seal against the cavity and back plate. Once the cavity wears to a certain point that seal is lost and water bleeds internally from chamber to chamber. At this point it's not rebuildable, the pump casting is done.

With a dial caliper measure the depth of the cavity to the flange the back plate mounts to and compare to the width of a new impeller. You want the impeller to be a couple of thousandths greater.

We can talk about reduced flow to the exhaust during warm up another time.

[dcsavitzky]

Thanks to Neil, Jim, and Tom for your thoughtful replies. When I get back to the boat next week, I'll try refilling the system and clamping the recirculation off and running it again. If that doesn't work I'll measure the depth of that cavity against the thickness of the impeller. When fully inserted the impeller extends a smidge out of the cavity and looks to be compressed by the back plate.

David

[zellerj]

I found an easy way to put the pump plate on without having the flimsy gasket get all messed up. Place a couple small binder clips on to the pump plate with the gasket. The binder clips hold the gasket in place and allow you to get a couple of screws started. Once a couple of screws are in a few turns, remove the binder clips and the gasket will now be held by the screws. Easy peasy.

I always dreaded changing impellers because the gasket would get messed up while I stood on my head getting screws started.

If you don't know what I mean by binder clips, just google it.

[ndutton]

When fully inserted the impeller extends a smidge out of the cavity and looks to be compressed by the back plate.

Exactly what you want.

[Al Schober]

Keep in mind that those Oberdorfer pumps DO wear out - takes a while, but they do. If new seals, shaft, impeller don't fix the pump - recommend you consider it dead. The Moyer ball bearing pumps are a thing of beauty.