How do I test to see if my water pump is bad?

So I pulled my boat out of the garage today to dewinterize it. I also changed the impeller. Problem is its not sucking up water. I pulled the pump cover and checked the impeller and everying looked good. So I worked my way back to the pump itself and noticed its not sucking water up. I tried priming but still no suction.

Any ideas of other testing I should do before I buy a new pump?

Your using a fake-a-lake to suck the water? I had a tough time getting mine to prime too. Ended up just loosening up the intake hose & cramming the garden hose in it with the water one. Primed fine. Since then I made an adapter out of Home Depot parts so the garden hose is hooked up directly to the intake hose. Works perfectly.

When you say intake hose are you talking about the hose that goes into the pump where the impeller is? If so I did take that hose off and took several gallons of water down the hose but it still didn't prime. Weird thing is I didn't see any water come out the exhaust when I poured the water in???I didn't try the water hose trick I'm sure that would probably be better.

And by the way I thought the pump was the actual transmission cooler. I just looked online and realized this. I was pouring water down the cooler which the hose on the bottom ran to the water pump. Not sure if that mattered or not.

The intake hose goes from the water inlet in the bottom of the hull into the v-drive or trans. What boat are you dealing with?

I usually just loosen the hose from the v-drive on my Vride, pull the hose & then mount the garden on the side of the v-drive so it's pumping water in the same way as if it were coming from the lake.

Pulled the intake hose today and stuck a garden hose down it. Water went through engine fine. Put hose back on Transmission cooler and hooked back up to fake a lake and no go. I'm lost to what it could be. Boat ran fine when I winterized it so its hard for me to imagine my pump all of a sudden just went bad? I looked in the tranny cooler and didn't see any blockage. Any ideas?

Put the fake a lake on the scupper so the water from the hose is shooting straight into the grate/intake.

raw water pumps don't to be primed. did you put the pump on backwards?

what year and model boat? it is possible like above said you put the pump back in backwards. the problem with running on the hose is that you are pushing the water though the motor instead of the pump sucking.

if it was backwards, it wouldn't let water pass through. It's not like an aerator ballast pump where you can force water past the impeller....

I've used the fake-a-lake for years and its always worked great. That said, I always make sure to set the height so that there is a good amount of pressure on the plunger portion to the hull of the boat. Also, I place the port where the water comes out of the fake-a-lake so that it is directly pointing into the intake scupper grate.

Also, I think sometimes if you turn the water on full force before you startup, the water pressure buildup will keep the plunger from sealing well to the bottom of the hull. So I just crack the water open a little, startup, then open the garden hose valve all the way after its running.

I had a fairly recent impeller seem to go bad on me at the lake and ended up hot swapping it on the beach. The impeller looked fine when I pulled it out, all blades intact. Put in the new one and backflushed the trans cooler and we were off again. Don't know quite what the problem was, but it seems good now. Maybe the impeller was spinning on the metal hub or something weird.

To troubleshoot, this is what I would do.

Hook up the fake-a-lake, disconnect the water line to the raw water pump. Make sure water goes through there. Hook the line back up, disconnect from the trans cooler, make sure water comes out there. You should have seen a bit more pressure coming from the output of the raw water pump.

Hook the line back up, disconnect the next line to (probably the thermostat) and see if water comes out there. If you have water pressure to this point, then it might be worthwhile to replace the thermostat/gasket if they have any age to them at all. I'm not sure how you can really diagnose the engine driven water pump, but if you've checked all the lines for leaks, the impeller gasket/housing for leaks, and water is getting to the thermostat...that might be the next place to concentrate your efforts.

Originally Posted by denverd1

if it was backwards, it wouldn't let water pass through. It's not like an aerator ballast pump where you can force water past the impeller....

wrong. have made this mistake myself once before.

well it will pull water out of the engine if thats what you mean. but the water hose will not push water past it. It's a positive displacement pump

How was the boat winterized? Could the hoses have been hooked up backwards? I ask because mine will suck antifreeze out of a bucket when I winterize. No pressure is needed.

Its a Indmar 351 direct drive. All hoses were put on correctly, I never removed the pump so couldn't be installed wrong. The only thing I changed was put a new impeller in. Pulled cover to see if it looked fine and if all fins were going the right direction. One thing I did notice and I'm not sure if this is normal since I never watched for it but the when I stuck the garden hose in the transmission cooler the water would suck down and then come back up like it would take some water then wait a few seconds and fill black up then take it all again. No leaks in motor when running, and water ran through motor great when I stuck the garden hose down the intake hose. With the fake a lake I can't imagine its not positioned right, I've used mine for 7 years numerious times and never had that problem before.

Is it something ridiculously simple like the scupper/intake is clogged?

You don't have a ball valve to shutoff the water coming through the Scupper do you?

I guess the other question to ask is, is the belt turning the pulley, or could the belt have gotten loose? I only ask this because on my old boat, the impeller would flip on occasion, and then the belt wouldn't turn the pulley that the waterpump is on. I would get a horrid squeal when this happened, though.

no the pulley is fine, impeller is truning the right direction. I gave up and made a appointment to have the shop look at it. They thought it was the impeller also but I would be shocked it it was.

If there is a leak at all in the system you will have suction problems. I nearly cratered my engine because of this. If there is anywhere in the system that air can leak in, the impellar will not get a positive suction. So it sounds like you may want check out your connections at the transmission cooler, pumps and scupper to make sure you have a tight seal. If it works fine with the garden hose stuffed in to the pump intake hose, after trans cooler, then you need to check the system from there back.

Also, check your trans fluid for water and make sure the trans cooler didn't fail over the winter and crack. I believe this would also cause an issue with your intake.

Its at the shop now so I'm curious to what the issue is. I didn't remove any of the hoses for th tranny cooler for winter so couldn't be leak there.

Impeller cover was getting a air leak causing the system to have suction issues.