Yamaha Thermostat Removal

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Yamaha Thermostat Removal

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Yamaha Thermostat Removal

Posted by Roger Ford on June 12, 2002 at 12:14:00:

Has anyone actually experimented with removing the thermostat from their 9.9?

Follow Ups:

Re: Yamaha Thermostat Removal Colin Swithenbank 14:48:01 06/13/02 (2)
Re: Yamaha Thermostat Removal Colin Swithenbank 14:47:02 06/18/02 (0)
Re: Yamaha Thermostat Removal Roger Ford 04:30:28 06/14/02 (1)

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Re: Yamaha Thermostat Removal

Posted by Colin Swithenbank on June 13, 2002 at 14:48:00:
In Reply to: Yamaha Thermostat Removal posted by Roger Ford on June 12, 2002 at
12:14:00:


Roger:[/i]

We've had problems with the thermostat sticking in both the open and closed
positions. Stuck open causes low engine temperature and carbonisation. Stuck
closed causes engine overheating to the extent that the oil pressure detector
registers low oil pressure and shuts the engine down to idle

I carry an infrared thermometer which registers cooling water temperature
non-invasively by pointing it at the outside of the thermostat housing

Removing the thermostat is achieved by removing the two 10mm bolts holding down
the thermostat housing. Lift out the old thermostat and replace it with a new
one. Its one of the easiest jobs on the engine
Colin

Follow Ups:

Re: Yamaha Thermostat Removal Colin Swithenbank 14:47:02 06/18/02 (0)
Re: Yamaha Thermostat Removal Roger Ford 04:30:28 06/14/02 (1)

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Re: Yamaha Thermostat Removal

Posted by Colin Swithenbank on June 18, 2002 at 14:47:00:
In Reply to: Re: Yamaha Thermostat Removal posted by Roger Ford on June 14, 2002
at 04:30:00:


Roger:[/i]

I had to dismantle an old engine and trace the cooling water routing to respond
to your query. I apologize if the following is far more than you wanted

The cooling water goes from the water pump at the base of the lower unit through
a metal tube into the base of the engine where it goes first into a water jacket
around three sides of the exhaust manifold. From here it splits into three
streams. Two come directly out of the aft port side of the engine as two nipples
(from which you can remove the rubber hose externally) without cooling the
engine. The third stream goes up into the center of the engine and cools the
cylinder walls then to the thermostat. A rubber tube from the thermostat housing
then sends the water to join that from the two nipples in an external manifold
of rubber tubes. There are three exits from this manifold. One goes to the
“indicator stream” out the side of the engine to show that the water pump is
working. The other two are attached to two short pieces of tubing under the
engine which direct the water as a spray to cool the oil tank

Meanwhile, the exhaust goes through the oil tank (warming the oil and cooling
the exhaust) into the lower unit where it mixes with the cooling water. The
mixture then exits through the prop. The external temperature of the lower unit
is quite a good measure of cooling efficiency

When a cold engine is started the cooling water fills the engine but little
water finds its way past the thermostat (to allow fast warm up), and virtually
all the cooling water by-passes the engine, coming out of the two nipples (see
above). When the engine reaches operating temperature the thermostat opens and
allows water up through the engine

The consequence of this water flow is that the temperature of the water coming
out in the water indicator stream is not necessarily that of the engine,
however, the water coming out the thermostat housing represents accurately the
temperature of the water cooling the cylinder walls. A second surprising
consequence is that a good flow of water from the indicator tube does not
necessarily mean that the water is cooling the engine! Water must flow from the
thermostat housing outlet

I have not measured the temperature of the water from the indicator tube. I have
measured the temperature of the outside of the thermostat housing with an
infrared thermometer as the engine warmed up and graphed the results. To my
surprise the engine takes a full ten minutes to warm up to about 140 degrees
Fahrenheit with an almost linear rate of rise of temperature, and the oil
probably takes even longer than this to warm up. We try to run our engines at
low throttle settings for at least fifteen minutes after starting to allow good
warm-up, and idle for at least three minutes before shutting down

I have found thermostats to be prone to failure. If they fail to open the engine
and oil overheat and the low-oil-pressure safety system starts cutting the
engine down to idle

The engine I dismantled I had replaced due to cooling failure. It turned out
that the rubber water pump impeller had broken up and I found the pieces of
rubber blocking the cooling tube at the point where it entered the engine. If I
had removed the lower unit and applied compressed air to one the two nipples
(see above) I would probably have been able to clear the blockage without
disturbing the powerhead to lower unit gasket. Also, salt buildup on the side of
the oil tank where the cooling water impinged was over half an inch thick,
probably comprised of aluminum and magnesium oxides with sodium chloride

Charles Kanter (see article in POA site) recommends cleaning with vinegar. I
have used oxalic acid. I’m not sure either of these is the answer and solicit
other suggestions

Colin

Follow Ups:

Re: Yamaha Thermostat Removal

Posted by Roger Ford on June 14, 2002 at 04:30:00:
In Reply to: Re: Yamaha Thermostat Removal posted by Colin Swithenbank on June
13, 2002 at 14:48:00:


Colin: Did you find that the temperture was consistent in your readings? Have
you ever taken the temp of the cooling stream to see if a higher than normal
reading gave an indication of problems?
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