engine

[johnyp]

Hello
Can someone help
I have recently started boating again and bought a 15 hp mariner 2 two stroke approx late eighties model as usual the seller promised me it was sound and like a fool i travelled 280 miles round trip for it anyhow i took it on the river to try it out and it started an ran great then it stopped pumping water after i had put it on full throttle for about five minutes so i turned it off and rowed back when i got home i checked the impeller and it looked ok but changed it anyway i also took the thermostat out and put it in boiling water and that opened up.
I have not tried it since but wondering if it could be anything else before i take it out again.
Any advice much appreciated.
John

[paddlers]

I have a 2005 Mercury 15hp 2 stroke and was warned to expect sporadic flow from the tell tail. Something to do with the design of the thermostat and not having a bypass like a poppet valve. I can't say for certain that your year model is the same but I've had no issues with mine!

[johnyp]

Cheers mike if i understand you right do you mean you keep going even if the water is not pumping out
John

[Landlockedpirate]

Try a search on here, some of the identical Mercury engines only have intermittent cooling when needed.

[Fenlander]

My experience of the Mariner 15 was that the intermittent flow was only at idle and the slowest trolling speed... once delivering power it was a constant jet.

[John Kennett]

Have you checked that the telltale outlet isn't blocked? That can sometimes give the illusion that there's a cooling water problem.

Did the block show any signs of overheating? If you've got a total cooling failure your engine will get very hot very quickly!

[uncle al]

If you have put the thermostat in boiling water it is now what we called buggered, you need to replace it.

[johnyp]

It stopped pumping water at full throttle i have checked and all the system is clear and the impeller was ok but i have still changed it i must ask the question as to why the thermostat will be buggered do to being put in boiling water cus i was told to do this by a boat dealer.
cheers
john

[paddlers]

Have you tried attatching a hosepipe to the pipe that runs from the impeller up to the powerhead without the thermostat fitted to see if the water circulates freely? Also that the impeller is rotating properly, some cheap models can spin on the brass centre. I've dipped mine into boiling water on a piece of string before with no apparent ill effects to check them.

[johnyp]

Hi thanks i will try it without the thermostat i have also pur an air line on it and it was all clear.
I have read that not all engines have a thermostat does this mean it does not need one and can be run without.
Cheers
John

[paddlers]

If it's got one it's there for a reason. Make sure it's working and fit it.

[9D280]

main reason is to warm it up quicker.

My old clamshell type ran from it;s inception to something like the last but one year of production with thermostat & poppet valve. The last year or so (I'm sire someone like Uncle Al can confirm exact dates!) the two were dropped, to the point the castings they sat in changed.

I was rebuilding & went for the "latest level" on the rebuld - Differences are now it dribbles at idle (used to squirt) and I had to up the idle mix by about 1/8 of a turn to offset the overkill cooling with the poppet valve essentially permanently open.

But I am mostly crusing, so low speed cooling efficiency is a lower priority for me.

[Fenlander]

My opinion... if they are fitted with a stat keep it.

There can only be so many reasons why you have no water at the tell tale.....

As others have said double check the impeller is actually being driven and not spinning on its bush or failing to be driven by the shaft.

I wonder what you are probing the tell tale with... I find a bit of Bowden cable inner ideal as its strong and flexy.

The intake isn't blocked in any way?

Is the powerhead to pump pipe in the leg joining OK after the lower unit was replaced?

I guess my next move would be to remove the gearcase again then flush down from the pump out through the inlet strainer... then remove the thermostat and flush through from the pipe in the leg to the powerhead and also from the stat housing back down the leg pipe.

[uncle al]

johnyp it will be buggered because you have cooked the wax in the thermostat bulb, the proper way to test them is, look to see what temprature is stamped on thermostat, with a thermometer and thermostat in container of water slowly bring up to temprature and watch it open /not open. I used to get some hot water from the coffee machine check the temprature and imerse the thermometer into the water.

[beerbelly]

my mercury 15 2006 year pumps water strongly and constantly when cruising or flat out but if I slow to 5mph it stops and flows intermittently I have been told its as it should be

[Fenlander]

I'm servicing my Mercury 15 today so have the workshop manual open.

Interestingly it gives the water pressure spec with and without thermostat. At 5000rpm the pressure is the same with/w.out at 5-7psi however at 750rpm idle the spec is 0.5 to 1.5psi with a stat and 0 to 1.0psi without. Seems if you take the stat out you are losing pressure to the tell tale??

[johnyp]

Hi all thanks for your comments/advice i have checked all of these and will give it a try this weekend let you all know how it goes.
thanks again
johnyp