Outboard cooling water (15hp)

[Sybaris]

Mariner 15hp, 2 stroke circa 2000

After not being used for the winter our outboard started fine on the first try so all seemed well and fine, but then I noticed that there was no cooling water coming out the back.

I removed the leg and checked the impeller which looked like new. Still no water. I then removed the thermostat cover and found that the hose exiting the thermostat (the tell tale hose) was totally blocked. Fixed that and assembled everything. Now water it coming out through the tell tale hose fine.

Question: I can't really remember if it also should come out through the exhaust pipe?

Question: There was no thermostat in the thermostat housing (I bought the outboard second hand 2 years ago) or is that only an optional thing on some models?

 

[VicS]

Properly identify the year from the serial number and THIS WEBSITE

Check the parts list at Crowley marine ( BUT I think it will will only be there if it is an American or Belgium made model) for the thermostat and gasket details

Get the thermostat and gasket and fit them.

Most of the cooling water exits underwater with the exhaust where you wont see it but I'd expect to see a little blown from an exhaust pressure relief port.

 

[Sybaris]

Update.

I bought a service manual on line. The thermostat seems to be optional, it is refered to as "if fitted". It also seems as if the cooling water should come out only through the "tell tale" hose, so I think all is fine.

Cheers

 

[VicS]

I think you fill find that the telltale is just that.
The bulk of the cooling water exits I am sure, like other similar water cooled outboards, below the water where you won't see it.

I am very surprised that the thermostat is optional.
I'd have said it was more likely it had been removed because the engine was overheating however if the manual says its optional....!?
Are you reading a manufacturers manual specifically for that engine or a copy of some third party manual that covers umpteen models including small ones that don't have thermostats. If the latter chuck it and get an OEM manual

What controls the engine at its correct working temp if there is no thermostat?

 

[Sybaris]

I bought a proper service manual on-line. It is the Mercury service manual 6/8/9.9/10/15 starting model 1986 (300 pages). Mine is a Mariner (identical) 15hp 2 stroke from 2000.

The manual mentions in various places "thermostat (if equipped)".

I have enclosed a drawing of the thermostat housing and tell tale hose.

I am a little confused here because my memory tells me that quite a lot of water normally came out of the tell tale hose whereas now it is only a trickle (but it is quite warm). Now if there is no thermostat installed or it had been removed sometime in the past because it was overheating that implies that without the thermostat most water would always go through the engine and not out the tell tale. Is that correct.

I will check with the previous owner, but it seems to me as if you don't have a thermostat it should at least not overheat, so why is it really then needed to begin with?

 

[VicS]

but it seems to me as if you don't have a thermostat it should at least not overheat, so why is it really then needed to begin with?

Not having a thermostat is no guarantee that it wont overheat but it is needed to ensure that the engine operates at its correct temperature.
If the pump is good and the water ways clear without a thermostat there will be no control of the water flow and it will run cold!

Having said that it is normal for the very small engines not to have a thermostat though. I would expect that to apply to perhaps 4 or 5hp and below only.

I have checked the various parts diagrams and lists for year 2000 15 hp models all show a 120 degree(F) thermostat part number 14586.


"thermostat (if equipped)" seems a very vague statement. Is this really a genuine manufacturers service manual ?

My advice to you would be to obtain the above numbered thermostat and the "gasket", part number 62386, and fit them.

 

[rudolph_hart]

I bought a proper service manual on-line. It is the Mercury service manual 6/8/9.9/10/15 starting model 1986 (300 pages). Mine is a Mariner (identical) 15hp 2 stroke from 2000.

The manual mentions in various places "thermostat (if equipped)".

I have enclosed a drawing of the thermostat housing and tell tale hose.

I am a little confused here because my memory tells me that quite a lot of water normally came out of the tell tale hose whereas now it is only a trickle (but it is quite warm). Now if there is no thermostat installed or it had been removed sometime in the past because it was overheating that implies that without the thermostat most water would always go through the engine and not out the tell tale. Is that correct.

I will check with the previous owner, but it seems to me as if you don't have a thermostat it should at least not overheat, so why is it really then needed to begin with?

I'm not certain that this will help but here goes:

I have a Mercury 15hp of the same year, which I'm told is identical to the Mariner - so much so that I was given a Mariner handbook with it.

When I bought it (9 years ago) the dealer told me that the water telltale won't always squirt, and that has proved to be the case - notably on tickover, when it will squirt for a few seconds then stop completely for a few seconds.

Hope this helps.

 

[VicS]

When I bought it (9 years ago) the dealer told me that the water telltale won't always squirt, and that has proved to be the case - notably on tickover, when it will squirt for a few seconds then stop completely for a few seconds.

You won't get a full flow from the tell tale until the engine warms up and the thermostat opens.

 

[Sybaris]

Rudolph,
Thanks you have the same engine so that was great and useful information. Do you only get water through the tell tale or does it also come out with the exhaust in the hole just it bit lower down?

VicS,
I checked with the previous owner and you are right, there was originally a thermostat which a mechanic removed somewhere in the Red Sea where no spares were available. He then decided it was ok without as he only cruised in warmer climates, which is the case with me as well.
I will however most likely get a thermostat when I have a chance, but for now I think it is fine.
Since I am without a thermostat should I have more or less water through the tell tale? I would have thought that with an open thermostat (or none) most of the water would go through the engine to cool it and out by the prop somewhere instead of out the tell tale, or does full force at the tell tale actually mean that the thermostat is open. Confusing!

Sorry about dragging this out but it is interesting.
Cheers

 

[VicS]

Confusing!

Sorry about dragging this out but it is interesting

.You actually have the advantage over me in that you have had the thermostat cover off and should know what's what and where in there.

It appears that the telltale is on the cover and therefore will only get water to it when the thermostat opens but perhaps I'm wrong.

The owners manual, at least the one I found on line but I think refers to your engine, said something along the lines of not getting much, or any, flow until the engine warms up.

I'd assume therefore that without a thermostat you'll get a good flow from the telltale all the time.

I know OMC engines better and they have the telltale taken from quite early in the cooling circuit, well before the thermostat, so it pees at full pressure as soon as the engine is started. They mostly also have pressurised cooling systems so you get a strong jet from a relatively small hole! I did not notice any pressure control when looking at the diagrams of yours.

 

[rudolph_hart]

Rudolph,
Do you only get water through the tell tale or does it also come out with the exhaust in the hole just it bit lower down?

Sorry, I haven't looked. However, the dealer did say that the 'peeing' will be intermittent and if it stops for a while, it's quite normal. This tends to confirm VicS' statement that a thermostat is opening & closing the flow of 'pee'

At the risk of jinxing the damn thing, I have to say that - peeing or not - the only item to fail has been the recoil starter cord. This in spite of my 'servicing' it (new plugs, clean fuel filter, change gearbox oil) myself last winter for the first time in 9 years.