Merc 15 2st Impeller Fitting

[HighlandR]

Since the temp of the stat is 120, it should'nt be open when starting from cold should it ! ??

[HighlandR]

There is quite a strong water pressure at the outlet ( without the stat fitted ) I wonder if the water pressure is actually opening the valve and causing it to constantly flow ?

[paddlers]

The 135 & my new Tohatsu pump water constantly but my Merc 15 2 stroke is intermittent. As long as you're getting good flow through the engine I wouldn't worry!

[dave3235]

Originally Posted by paddlers

The 135 & my new Tohatsu pump water constantly but my Merc 15 2 stroke is intermittent. As long as you're getting good flow through the engine I wouldn't worry!

Hi all

On my mariner there is a little hole on the side of the leg.Is the stat in the right way

[HighlandR]

Hi Dave, yes the thermostat on this engine only fits one way, if it were put in the other way the housing wouldn't close.

I'm puzzled !

[paddlers]

Type into Google 'water pressure relief on an outboard' and all should become clear! Logically there has to be a bypass on the thermostat as the impeller pumps constantly when the engines's running.

[HighlandR]

Hi Paddlers, googled water pressure relief, good info it explains alot, however i'm still confused about the thermostat, if water is constantly flowing from the tell tail I'm thinking there isn't much point in having a stat on it at all, unless the by-pass is accounting for some of the water? - I have no idea, but I suppose having the constant flow will make it easier to keep an eye on cooling.

[paddlers]

It's obviously part of the design of the engine to direct water flow and optimise the heat generated by combustion to make the thing operate more efficiently!
I'm certainly no expert on these things but manufacturers don't spend/design things that cost money unless they have to. Personally if it's got one I'd want it fitted & working.

If you've got a good flow from the tell tale with it fitted that'd do for me.

[beerbelly]

I have just had fitted a new impellor and stat in my mercury 15 and it doesn't pump any water out of the tell tale for at least a minute then pumps strongly . the stat is only there to help the engine to get to optimum operating temp quickly then to maintain that temp .even without a stat fitted it would be up to that temp within 5 minutes .once the engine is up to temp unless just ticking over the stat will remain open most of the time I wouldn't worry you have a strong spout of water out of the tell tale that's the important thing

[HighlandR]

Yes I have to agree it does make me feel better about having one fitted if it's been designed to have one!
Just one last question on the impellor subject, if out on the water happily speeding along and for some reason the water system got blocked by debris etc and if by chance you weren't to notice the tell tail had stopped, are there any signs that signal overheating ? so that you would know to cut the engine.

Once had a car that over heated often ( having 3 holes in the radiator didn't help ) I remember the engine began to make a sort of humming noise as it got hotter which signalled for me to stop and give it another drink.
Do these 2 stroke outboards have any similar signals before causing damage ?

[A1an]

Engine revs start to drop as the engine tightens up on its way to seizing solid.

[paddlers]

A1an is spot on. Any change in engine note would be your first indication of anything overheating.
Happened to me one time ! No tell tale and engine spluttered, turned out to be the rubber pipe to the tell tale exit came off spraying water onto the plugs/electrics ..... Cue huge relief, a cable tie sorted it!

I tend to look at the tell tail on start up then pretty much forget about it once it starts. To me it indicates the impeller is working & that's good enough, it's impossible to watch that and where you're going!

[HighlandR]

I'll add a few cable ties to the kit list just incase!! nice one

Almost ready now for the big first day !

Had to make a wooden keel as the original one had been lost years ago, took a bit of time to get it just the right fit but all is good now, just a few finishing touches with the plane to smooth things up, few coats of varnish and she'll be ready.

Been looking a while for a trailer, rather than having to setup and pack away each time, and was lucky enough to pick up an old motorbike trailer that looks like it will be suitable. Just replaced the wheel bearings.

From other trailers I've seen on the forum, don't think it should be too hard to add some planks/bunks to sit the boat on. Trailer is only 3 feet wide, but the tubes are 4ft on centres underside, will try figure something to make it fit !