Replaced water pump impellor but no cigar

[Keebo]

First of all let me say thanks to everyone who takes the time to post useful info. I looked through the last few pages seeking an answer before I posted but cound find what I needed. I did find enough info on how to change the impellor out so thanks for that.<br /><br />I have a Mercury 650 four cylinder that was taking nearly a minute to start flowing water out of the p-hole and would not pump a strong enough of a stream as it should. It would flow at slow speeds but at higher speeds it would stop. Slowing it down would not yeild any flow but steam. Turning the engine off for a spell to cool and then crank it again would start the same cycle over again. I replaced the water pump impellor but it is still doing the same thing. The tube is not clogged up as I blew smoke through it while the lower unit was off. The smoke did come out of the driveshaft (?) opening and not the orifice going to the water pump housing like I suspected it would if that makes a difference. The parts guy told me it may be my thermostats. If anyone can help I sure would appreciate it. Thanks.

 

[wilde1j]

Re: Replaced water pump impellor but no cigar

If you didn't do a complete water pump rebuild (liner or housing, wear plate, impeller, gaskets) you should have. It doesn't take much scuffing or scoring to make the pump ineffective. If your motor has thermostats, they're easy to check. (Put in water on the stove and measure the water temp when they open). Most outboards want 140 to 150° F, but a shop manual will tell you exactly.

 

[Keebo]

Re: Replaced water pump impellor but no cigar

Thanks for the reply. The water pump unit was replaced a little over a year ago and still looked to be in good condition with the exception of the impeller, which was no longer flexible. I will check out your stove tip when and if I find the thermostat(s). I might as well buy a repair manual now that I plan on doing all of the repairs that I can on this engine. Which manuals seem to be the best?

 

[erniex]

Re: Replaced water pump impellor but no cigar

I just had a similar problem on my old Merc850. Turned out the the impeller was not spinning at high revs. The drive shaft had worn enough in that area opposite the flat and key over the years that it allowed enough play for the shaft to spin inside the impeller bushing at high rpms. Stuck me out in the middle of the lake! Lucky I had my trolling motor. Had to rework the shaft to take out the slack.

 

[Dartboy]

Re: Replaced water pump impellor but no cigar

It may be daft, but a polite suggestion, was the impeller fins fitted in the correct rotation. Meaning the fins trail behind the rotation direction (clockwise).

 

[dingbat]

Re: Replaced water pump impellor but no cigar

was the impeller fins fitted in the correct rotation. Meaning the fins trail behind the rotation direction (clockwise).

It does not matter which direction it's installed in. It will "right" itself the first time the shaft rotates

 

[Keebo]

Re: Replaced water pump impellor but no cigar

Thanks for the comments guys. I replaced the impeller the same direction as the one that came off. The key and shaft looked like what I would expect a good one to look like meaning it was flat enough to hold the key in place. Any suggestions on which brand of manual to purchase?

 

[emckelvy]

Re: Replaced water pump impellor but no cigar

#1, this motor ain't got no 'stat!<br /><br />#2, I had a similar problem to erniex with my old Merc 1000, it had an 800-4 lower unit on it and spun the impeller out on Jul 4, 1984 when I was slalom skiing. You never forget the sound of an Inline thermo-nucleating at full tilt!!!! Had it back up and running the next weekend, those were the days!!<br /><br /><br />On to the strange overheating problem, I doubt there's any issues at the impeller end. If everything down there looked normal, no unusual wear or slop, it's probabaly OK. These old Merc pumps aren't that picky, and it's got to be pretty bad before you don't have water pumping with a new impeller installed.<br /><br />I believe the issue lies in the water passages of the block. Either the block is silted up and is having circulation problems, or there are issues with the exhaust manifold gaskets or a leaking exhaust plate. <br /><br />If the exhaust side was blowing into the coolant passages, it could blow the water out of the block. Thus the very long time to 'spool' up and get water out of the telltale after you first start the motor. <br /><br />You may or may not be able to get at all the bolts well enough to be able to remove the rear cover on the block, or the exhaust side cover/plates for inspection. <br /><br />Likely you'll need to pull the powerhead. Mandatory if you're in a salt area; those bolts will not come out easily. If fresh water only, you'll probably have little trouble getting it apart. Heat does wonders for freeing up stuck bolts, BTW. Be advised if you break bolts and can't get the busted nubs out with head and Vise Grips, the only correct repair is to drill out the broken bolt completely and install a Heli-Coil or similar insert. You can't drill out stainless and tap to original size, the stainless has to be completely gone before you can thread holes with a Heli-Coil tap.<br /><br />Anyway, to quote Forrest Gump, "that's all I've got to say about that".<br /><br />BTW don't run the motor any more until it's sorted out, as you will fry the rings and pistons.<br /><br />HTH and let us know what you find.

 

[Keebo]

Re: Replaced water pump impellor but no cigar

A lot of good info there , Ed. Sounds like a lot more risk of me making matters worse if I need to yank out powerheads and break off bolts (which will no doubt happen) on my second venture into outboard repair. Last time the shop installed the water pump they said the exhaust system was no good but said it shouldn't be a problem other than being louder than normal. That might be where the problem lies. Thanks for letting me not waste all day looking for thermostats that don't exist. Perhaps I'll save this job for the shop if I can't see anything already mentioned. Thanks for all of the suggestions.

 

[rodbolt]

Re: Replaced water pump impellor but no cigar

ding bat is a dingbat. the impeller will not right itself in your application.<br /> take it someplace that has a good tech.<br />good luck and keep posting

 

[wilde1j]

Re: Replaced water pump impellor but no cigar

If you're interested (still) in a shop manual, the Merc OEM manual, available from Merc Parts Express is the only manual to get. The third party stuff if junk.

 

[Keebo]

Re: Replaced water pump impellor but no cigar

Thanks for the suggestion Jim. I still want to get a manual for the easier repairs.

 

[dingbat]

Re: Replaced water pump impellor but no cigar

the impeller will not right itself in your application

Rodbolt, <br />Has does this assembly differ from any of the Alpha drives?