Glen-L.com

Hi, a quick question regarding the cooling system of a merc 4.5 hp.
I replaced the impeller. The motor starts, and runs fine. The thing is that at the tell tale hole, when running, the pee stream is weak at best, and today the water that was coming out was steaming hot. I stopped the engine immediately and took it home. When I manually blew through the tell tale, while covering the other end, it was not a sealed system. I mean it would not hold air. I would think that any water cooling system should be a sealed system. When it operates no air should be in the system? Am I correct? I am NOT an engine expert. I do have the manual. Maybe it's missing a seal or something? Thanks for any input.
RJ Lemay

Your wear plate maybe worn along with the housing. I would also look at the pickup and make sure that the screen in the foot has not corroded shut. I am not sure if that engine has a thermostat. But if it does, the thermostat can also be weak and worn which also causes it to sit sideways in the seat which blocks flow. Is this engine a four stroke too? Check the hose running from the block to the pee tube too. If its aged, it could have collapsed inside. Sand or crust can form if the engine has been sitting around too. Check with your dealer for a chemical call Saltway which goes in the water for flushing. Age of engine? The only problem with using this in an aged engine is that it can do more damage from releasing crusty corrosion thats formed in the dead areas from sitting.

http://www.saltawayproducts.com/

http://www.saltawayproducts.com/Page14.htm

It's always best to replace the gaskets and seals on the waterpump at 4 year intervals.

No, it is not a "sealed" system. This is considered a "raw water" system or "open" cooling.

Water is sucked into the waterpump through a pick-up tube just under the cavitation plate. The impeller forces the water up a tube (by displacement at low rpms and centrifigal force at higher rpsm) to the base of the powerhead (just behind the carb).

From there it travels through channels to the water jacket which surrond the cylinders. Some exits the tell-tale to let you know water is flowing with the rest going into the exhaust and down the leg (helping to cool the exhaust and acting as a muffler by creating a wall of water that absorbs the sound).

This model did not ship from factory with a thermostat and there are no check valves etc anywhere in the system - so air would flow freely in either direction if you were testing.

Your symptoms are (normally) indicative of a bad seal (cover seal where the water tube enters is the leading contender) or as noted a clogged pick-up or even build-up in the water channels (particularly if the motor has ever seen salt).

But, "IF" all was fine before you replaced the impeller the odds are high that the waterpump cover did not seat properly or the impeller slipped it's key when you reassembled...

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Graham

Yes, Plywood is "real" wood

A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it

Thanks Graham, I have a 6 and a 4 hp Merc that I need to replace the impellers.

The 6 supposedly had the impeller replaced by the previous owner,but wasn't pumping water to his surprise when I bought it.I'll look at the housing and key when I replace the impeller myself.

The 4 ran good,but I just want to replace as it's been a few years

_________________
Boat building can best be defined as an endless series of
tragedies obscured by the occasional miracle, followed by a good bottle of beer.

Don't Dream Your Life, Live Your Dream

Guys,
I think he is talking about the 1977 Merc 45 that he was given.

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A secret to a good marriage is to have a quick mind and a slow mouth!!!

I think you are right....and it still sounds like it has a problem

_________________
Boat building can best be defined as an endless series of
tragedies obscured by the occasional miracle, followed by a good bottle of beer.

Don't Dream Your Life, Live Your Dream

Alright smart ---. Just because you cut a little plywood the other day doesn't give you the right to start picking on people. BTW, how much saw dust did you make. Maybe a tablespoon. I'm going back to the garage where I belong.

_________________
A secret to a good marriage is to have a quick mind and a slow mouth!!!

Wasn't trying to be smart....just following his thread and noted what Graham was saying!!!

_________________
Boat building can best be defined as an endless series of
tragedies obscured by the occasional miracle, followed by a good bottle of beer.

Don't Dream Your Life, Live Your Dream

My bad. I thought you were picking on me. Saw where Oyster asked him if it was a 4 stroke. That is why I posted the year.

_________________
A secret to a good marriage is to have a quick mind and a slow mouth!!!

Mercury has made many engines over the years and other manufacturers has made engines for Merc too. I really cannot keep up with the numerous buyouts and pitfalls that Mercury has been through over the years, hince my many areas in which I replied. I remember the time that Mercs were the absolute worse in the industry for saltwater use too.

That's why I don't want to use my antique Mercs in saltwater....although i may the 6HP as it has been used there,and I'm not that picky about it for the money I have in it.

_________________
Boat building can best be defined as an endless series of
tragedies obscured by the occasional miracle, followed by a good bottle of beer.

Don't Dream Your Life, Live Your Dream

Naw....you'd know it if I was picking on ya!!!

_________________
Boat building can best be defined as an endless series of
tragedies obscured by the occasional miracle, followed by a good bottle of beer.

Don't Dream Your Life, Live Your Dream

It may seem overly obvious, but be sure the new impeller was installed with the blades bending the right way. As silly as that sounds, getting them in there backwards seems to be pretty common.

Other 2 really likely culprits will be the O rings on the cheesy-crumbly-old nylon riser tube that connects the pump to the shaft housing, or that tube itself. There are a couple of kits for that vintage, Merc was running some sort of "part-O'the-week" club during the mid 70's, and getting the right parts can be a problem. May want to get a whole new kit (inc housing, connector tube, and wear plate) from a merc dealer-be sure they check for superseded part numbers, and lookup by S/N, not just model.


It shouldn't be sealed to air only plugging one end. The water will also exit the idle ports. (be sure no critters made a home in the port.) At idle the exhaust, and water are diverted above the waterline to overcome water pressure. If the ports are plugged, the exhaust pressure will blow the system down at low speed, sometimes you will see a little exhaust in the water coming out the bleed-tube, sometimes not.


My bet is impeller backwards, or tube not seated right.

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Some plan to stroll through Saint Peter's Gates, I plan to go through them at 150mph... backwards... in a screaming ball of flame, with a glimmer belt wrapped around my head, and a NOx button in my hand.

thanks guys,
yes it was the 1977 merc, given to me. The key might have slipped? Maybe the pick up tube or seal. I'll yank it apart tonight again and pull out my magnifying glass to check everything close up. Thanks for the help!
RJ Lemay

Yes, figured it was a 1970's model 45 (4.5 horse).

There waterpump is considerably different than (portable) Merc's built after 1985.

This waterpump has no seal between the cover and the plate so you do need to really snug it down without "reefing" but first make sure that the mating surfaces are good and clean so that the "plate" gets sandwiched snugly between the cover and the base.

It does have a "cover seal" (sometimes referred to as an oil seal in parts manuals) where the water tube enters the cover and a seal where the driveshaft enters the cover - either could be shot.

But again, if it was working fine before the impeller was swapped, a slipped key is pretty high on the list of things to check.

Agree that if an old impeller was re-installed backwards can cause an issue (because the vanes, at this point, will not correct themselves), but with a new impeller, even if you twist the driveshaft the wrong way to get the cover on, it will right itself on first use without issue...

_________________
Graham

Yes, Plywood is "real" wood

A "professional" is someone who gets paid for their work - it doesn't necessarily mean they are good at it