BillR

I just had both impellors on my 496HO's replaced. I can't get the darn things to circulate water correctly on the hose without revving it up to 2000 rpm.

When I put them in the water for the first time, I had to rev the motors for them to pull water. Once they primed, it flowed water very well all day long. Pulled the boat out after about 2 hours of running to clean and flush. Hook up to hose, they won't flow water unless revved to 2K. Of 2 motors, port one pulls water off the hose a little bit better.

There are two of us down her that have this problem, me and Vyper340. We both had impellers just changed. We both have this exact same problem.

Old impellers looked good, but we felt better replacing.

Water pump housing has grooves on each end where impeller rotates. Our tech says the impellers need some time to seat themselves, but should be fine.

I know for sure we have NOT burned up an impeller.

alter ego

I just went through a similar situation with my 502. I ended up replacing the pump housing along with the impeller. It pumps perfect now. We almost replaced the impeller only but I was told that it probably wouldn't solve the problem. How long have you had the boat? I hope this helps...

BillR

I bought it new in Nov. 01.

alter ego

I just went and found my old housing and it had some fine grooves in it where the impeller sits. Thats probably why I had to replace it. I read through the other thread with the same problem...There are a lot of people going through this.

Kentz

Bill we've discussed this before. I'd have to look for my old post, but my 01's do the same thing. I will NOT attempt to run them on the hose.

You're right if you dont keep the revs above 1500+ you'll loose the impellers. I had my entire pumps replaced @50hrs. Sure looked like bad machining to me.

Wouldn't you think you need considerably more water psi through the xchanger and t-stat to get good gpm flow(versus t-sat only)?

Reckless32

Try placing some duct tape over the "lower" pickup holes as recommended by Merc and see if that helps during flush. Just don't forget to remove when done.

Bill I had helped troubleshoot our friend Mark's 22 Scarab with the 454 a couple of years ago. After replacing the impeller and still not getting adequate cooling while idling or running on plane, I convinced him to just change the housing due to a "slight" grooving inside. Viola! Problem solved cooled great thereafter. Unfortunately it simply doesn't take much wear for these pumps to break suction and cause problems. I would try the duct tape, and if the results are the same, cut your losses/efforts/doubts by replacing the housing and moving on with a worry free summer season...Vype340 too...

BillR

I used tape to cover holes for more water.
I was prepared to replace whole pump. Dave L said not to. Said groove was not that bad to require replacing. He is a Merc Tech, I am not, so I went with his opinion.

I wonder if the impellors need to seat in??????