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Old 06 August 2014, 09:06   #1
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Merc 15 2st Impeller Fitting

Hi guys, got a used Merc 15hp 2 stroke here and need to replace the impeller.

It would not pump any water out the tell tail ( only for 2 seconds at start up and then stop ) the inlet / outlet and hoses have been back flushed with a hose.

I then removed the impeller housing as shown

I'm unsure as to wether any gaskets or washers are missing so have taken photos of the removal, so that you guys can see and advise if any parts are missing etc.

There were no washers on the shaft or impeller.

I'm also unsure of how the water intake pipe connects to the impeller housing, does it simply sit on top of the housing or should it be inside before the casing is bolted down.. or .. ?

When the gearbox was removed, the rubber part was left attached to the main intake pipe up inside the leg

The base plate has some ring marks on it from the impeller ( see photos ), is this still ok to use or should it be replaced ?

1 last thing, how is best to remove this hard glaze stuff like varnish off the parts?
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Old 06 August 2014, 09:08   #2
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2 more pics showing score rings
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Old 06 August 2014, 11:00   #3
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these engines don't pump any water out of the tell tale until the thermostat opens a couple of mins after starting then it will stop straight away when the cold water gets to the stat then a min later will start pumping again .I also noticed when going slow on tickover the stat will close again and interrupt flow
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Old 06 August 2014, 11:07   #4
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Hi Beerbelly, there is no thermostat fitted at the minute, the previous owner must have removed it. But still there is no water flow..
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Old 06 August 2014, 12:15   #5
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Merc 15 2st Impeller Fitting

If it were mine it put in a full water pump kit, usually the kits contain the pump base plate, impeller and all gaskets required then I'd chuck in a stat with gasket, waz it back together and see what happens.

Good clean up job by the way.
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Old 06 August 2014, 12:25   #6
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Alan how does the downpipe connect to the impeller housing ? Does that rubber piece come off the pipe ?
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Old 06 August 2014, 12:28   #7
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Merc 15 2st Impeller Fitting

The part in picture 3 looks like it should be on the top of the pump, can it fit through the raised triangular part.
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Old 07 August 2014, 02:04   #8
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That impeller, although probably needing replacement, is fully functional. Good idea to inspect and replace it either way though.

When you flushed the block thru the thermostat, was it pumping water out the tell tale? Did you push water into the tell tale fitting?

I am still gonna go with an intermittent blockage.
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Old 07 August 2014, 03:04   #9
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Yes Alan, the rubber part eventually came off the downpipe and looks like it should be inside the top of the housing - it wasn't when I removed the box.

Peter, yes water flowed strong from the pick up and also the tell tail, flushed it both ways for 15 mins each.
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Old 07 August 2014, 03:47   #10
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Enter your engine details into this site & you'll get to exploded diagrams of the engine. Might help with what should go where.
Evinrude Parts - OMC - Mercury Outboard Parts - Mercruiser Parts - Yamaha Marine
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Old 07 August 2014, 10:24   #11
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Thanks for that link Paintman, some good clear diagrams on here !

Still unable to identify the year or model but think I've eventually found a part number for the impeller kit : 47-42038 Q3 - from a company called Repower Marine.

This one looks identical to the one fitted so I will order that.

All I now need is a part number for the thermostat, but they don't stock them, any ideas guys ??

Where is best to buy parts here in UK ?
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Old 07 August 2014, 10:27   #12
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Should I fit a thermostat ( as the engine was designed to have ) OR should I fit a restrictor on the tell tail as mentioned, so that the engine still gets a good amount of cooling but also so it will have water flow from the tail as a visual aid ?
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Old 07 August 2014, 10:34   #13
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Merc 15 2st Impeller Fitting

Stat.

Engines and oils are designed to work at a certain temperature.

For parts try Blackdog Marine, he's a member on here, he goes by the name of Turbodiesel. If he hasn't got it he'll find it
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Old 07 August 2014, 11:43   #14
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Cheers Alan just emailed him
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Old 07 August 2014, 13:02   #15
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Thumbs up for Black Dog Marine ! Excellent to deal with. Did you sort the mystery of the piece on the end of the pipe?

Fit a thermostat ! It's designed for one.
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Old 07 August 2014, 14:21   #16
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Hi Paddlers, yes managed to get it off the downpipe, took my time so as not to damage it and finally came off - I'll be sure and grease it for ease of removal next time.
It should have been inside the top of the impeller housing, bit strange why it wasn't, but I'm guessing that would explain the lack of water flow since it wouldn't have been sealed properly.

I'll fit a thermostat, will make it harder to check if the impeller is still working, but as you say it should have one so that's what I'll do.
Just checking prices here, those little stats are pretty expensive are they not !?
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Old 13 August 2014, 11:14   #17
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Hi guys, managed to fit the new impeller kit and the engine now pumps a good strong constant flow of water from the thermostat hole.

I then fitted a new thermostat kit ( with new O-ring and gasket ) however, the water now constantly flows from the tell tail - it does NOT stop and start.

Engine started from cold, it pumps within 2 seconds and continually did so for 10 mins on fast idle ( with prop in gear ).

Does this mean the new thermostat is faulty ? I inspected it and the thing looks to operate fine, the spring holds the valve closed unless pressed hard to open it.

Help !!??
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Old 13 August 2014, 11:21   #18
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You can check the thermostat by dropping it in boiling water in a piece of string. They operate at different temperatures which may be stamped on it!
The only accurate test is to have a thermometer in with it but you'll soon see if it opens or not !
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Old 13 August 2014, 11:23   #19
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On my bigger engine there's a spring valve that I can't remember the name of that allows water to pass when the thermostat's shut.....!
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Old 13 August 2014, 11:37   #20
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Hi Paddlers, I dunked it in boiling water before fitting just to see if it opens and closes which it did. The temp stamped on it is ' 120F '

Does your bigger engine constantly pump water or is it intermittent like this engine is supposed to be ?
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