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99 hp thermostat

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rick_h_2

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"I have a 2001 9.9 mercury out

"I have a 2001 9.9 mercury outboard. It was pumping out water but it was extremely hot. I took out the thermostat and checked it on the stove.It was no good so I invested $32 on a replacement only to talk to a buddy who said his thermostat went, he took it out and it has never run better. And after cleaning the carb yesterday I ran mine without the thermostat for a short time and it ran perfect...Should I also leave mine out? And if so why did the engineers at Mercury put one in?"
 
"I have a 1996 9.9 Mariner &#4

"I have a 1996 9.9 Mariner (Yamaha) 4-stoke and the thermostat is extremely important. I fish lake Erie (trolling) in April and without the t-stat the condensation in the crankcase is so bad the oil becomes milky and overflows when the dip stick is removed. The t-stat opens and closes to allow the 40 degree water to warm in the engine.

Without knowing the conditions you fish, 2 or 4 stoke, it's difficult to say whether you need the t-stat in. I know I do."
 
"Merc never even installed the

"Merc never even installed thermostats on the 15 horse and under motors for a number of years (saved them a buck a motor I guess), but you should always run a thermostat.

Here's Joe Reeves (OMC master tech) explanation..

"(Thermostat Purpose)
(J. Reeves)

Many engines are considered high performance engines and demand a thermostat(s), and many smaller hp engines also require a thermostat for the following reason. The pistons actually distort/twist off round when running. The thermostat is required to keep the outer wall surrounding the steel cylinder, and the cylinder wall itself at a temperture to compensate for the distortion.

With the thermostat removed, the difference in temperture between the inside the cylinder and the water jacket quickly reaches a point whereas (in effect) you have a oblong piston running up and down a round cylinder, or vice versa. Bottom line is without the thermostat, the piston and cylinder wall could be damaged in a short period of time.

The thermostat in your car isn't there simply to have the heater function properly..... think about it. ""
 
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