Yamaha Malta outboard cooling water flow

[Sandro]

Hi all,
Last Sunday I bought an Yamaha Malta outboard from 1988. The seller (a private) said that the motor, from new, had been used one season in Greece on a RIB, then washed running in the lake and then no more used. At his premises we (my son and I) tested it in a bin. Everything worked correctly. The appearence of the engine is almost as new. We forgot (we stupid both of us! More so as Seagull owners!) to check the cooling water flow from the tell tale.

At home I remembered, and ran the motor again in the bin. No water.
I thought that, after so long time the impeller rubber could have degraded and checked it: it is good and supple. It came to my mind that, just after a cold starting, the thermostat could have been yet closed. I removed it and ran again the motor, in gear, at about 1/3 throttle (maximum possible in the bin) for about 1 hour. The temperature of cylinder and headstock, continuously checked by finger, was always cool. Very little water was sprinkled from the back-pressure relieving holes half-way down the leg.
There is also a small hole under the cylinder, in the casting conveying the exhaust to the leg. No water was outcoming from this hole.
In the meanwhile I tested the thermostat by heating it in a small pot of water. It opens OK.

I do not know this motor.
Is the above behaviour OK?
Where is supposed to be the cooling water tell tale?
What should be seen when water is circulating correctly?
Can I trust the motor as it is?
Or shall I clean the waterways?

After all it is not overheating.

I refitted the thermostat and shall test soon the motor on the boat for a long spell at cruising RPM and report here the outcome.

Thanks to all who will either remove my fears or warn me.

Best regards and fair winds.

Sandro

 

[MarcJ]

I take it you tried poking a bit of wire up the tell tale hole? On my yamaha it's on the back left side when looking at the throttle...

 

[Ric]

I have the same outboard. Very little water comes out at one third throttle - it just spits a bit. There is no continuous stream like on bigger outboards.

When I rinse mine at the end of the season, I take off the prop so that I can run it at full throttle to properly check the flow.

 

[CreakyDecks]

I don't know that engine but I do know that my Suzuki had me chasing non-existent faults when I ran it in a big bucket and saw only a drip from the tell tale. When it is on the boat, only submerged a few cm deeper, it shoots out like a four year old boy.

 

[VicS]

I echo what has been said above.

I am never quite sure what constitutes a "Malta"

If it does have a telltale then check it's not blocked.
Refer to the owners manual to confirm then existence of a tell tale and what you should see in the way of flow.

ITYWF 2hp models have no tell but should eject some cooling water from the exhaust back pressure relief port on the back of the leg below the clamp. Maybe just a spray or mist but not a steady water flow

3,4,and 5 hp models have a telltale on the under side of the power head assembly above the clamp. They should produce a steady flow of water at all times while the engine is running.

It is essential that the water pump is properly immersed and with fixed drive engines in small tanks or bins advisable to remove the prop so that turbulence does not affect the water pick up

 

[steve66]

Hi, It hasnt got a tell tale, it just emits a fine spray from exhausrt relief holes in the leg. I personally remove the thermostat entirely. A good indication if its pumping properly is remove the thermostat cover, start it up and you you will see if your getting sufficient water to the stat.
Hope this helps

I echo what has been said above.

I am never quite sure what constitutes a "Malta"

If it does have a telltale then check it's not blocked.
Refer to the owners manual to confirm then existence of a tell tale and what you should see in the way of flow.

ITYWF 2hp models have no tell but should eject some cooling water from the exhaust back pressure relief port on the back of the leg below the clamp. Maybe just a spray or mist but not a steady water flow

3,4,and 5 hp models have a telltale on the under side of the power head assembly above the clamp. They should produce a steady flow of water at all times while the engine is running.

It is essential that the water pump is properly immersed and with fixed drive engines in small tanks or bins advisable to remove the prop so that turbulence does not affect the water pick up

 

[Banyon]

I used to have one of these engines. I'm sure mine had a tell tale and emitted a reasonable flow of water.

 

[Eeyore]

Page 35 of the manual implies there is no tell tale, but there most definitely is! Mine was spitting water from the two pilot holes half way down the leg when it went in for a service. On completion of that service, the impeller had been replaced along with the impeller housing and the exhaust pipe. On start up, there was now a continuous jet of water from the tell tale hole on the underside of the power head assembly.

 

[sparkie]

In an attempt to clear up the confusion, the earlier Maltas did NOT have a tell-tale. I drilled one in the housing of mine when I first bought it as I didn't trust the "spray holes" in the leg. This confirmed that water was not flowing so I investigated further and found the impeller had disintegrated. If the motor is only used for short trips then it's easy to be unaware of this problem without a proper tell-tale, and this of course is then potentially disastrous if a long run becomes necessary. Good little engine, very well made.

 

[Sandro]

As usual in the forum, many useful answers!
Thanks!

In the manual I have, no mention of cooling telltale nor of flow checking while running.

I understand that my Malta is of the older model, without a large flow telltale, only back-pressure relief holes.

The pump does work: in the bin, when I removed the thermostat, with the old damaged gasket, before I made a new one, water was strongly sprinkling under the thermostat cover.

I ran the motor on the boat: about 5 NMiles, a little more than 1 hour and back, without the top cowling, continuously checking the cylinder temperature by finger. Always cool, except on the first half minute or so after starting - probably thermostat still closed. At the far end of the voyage an Yamaha dealer/boat-yard reassured me about the good working of the cooling system. He showed me on a 3hp Yam the telltale rubber tubing that mine have not.

So everything is OK.

Nonetheless I would like very much to actually see the water flow. Please Sparkie, where did you make the hole exactly? Did you also add a tube conveying water outside of the lower cowling?

I wonder if I'll do it because the motor looks as new, never disassembled, and I feel shy to disturb it.

One more worry: neither in the manual nor in the parts exploded view can be seen any safety shear-pin or else to protect from propeller hitting shocks.
Surely Yamaha envisaged something and I would like to know. Perhaps shifting in neutral?

Next projects on this engine:
- As I often sail single handed, replace the stop switch with one fitted with a kill cord as I already did on a Johnson 4 that did not even have a stop switch. Here it is easier.
- The motor in my Drascombe Dabber is in a well. It can be tilted out of the water just short of one of the steps provided. I shall make a new tilt support brace 10 mm shorter than the original so that the motor can be hitched in the step just before hitting the transom.

It amazes me that this motor (3 hp) with just a little throttle appears to push the boat much more than the Johnson (4 hp).

It almost reaches hull speed with less than half throttle and, if further opened, it does not increase RPM, as though it was overloaded.

As the Dabber is not a speedy boat and is rather hard to push, I think that a shorter pitch propeller than the original (7 1/4 x 6) would allow better exploiting of the higher RPM and give a better bollard pull against wind and waves at low speed.
Unfortunately Yamaha does not supply a choice of different propellers for these small motors.

Thanks again to everyone, fair winds.

Sandro

 

[Eeyore]

One more worry: neither in the manual nor in the parts exploded view can be seen any safety shear-pin or else to protect from propeller hitting shocks.
Surely Yamaha envisaged something and I would like to know. Perhaps shifting in neutral?

There is no shear-pin! The prop is bonded to a rubber bush on the splined drive sleeve - if you hit something hard, the bonding shears and a new prop is required. Not really a good design!

 

[Sandro]

Thank you Eeyore,

If it ever happens I'll tray and gluing again the rubber bush. One should succed in getting the wanted torque.
the problem is that you can't do it at sea and bringing a spare propeller is costly and not practical.
Perhaps on a broken propeller one can make a solid bush with a shear-pin and some shock absorbing rubber, or a spring, Seagull style.

Beware of submerged rocks or logs!

Sandro