Removing thermostat

[Triple R]

Anyone here remove their thermostat? I'm considering it if anyone has had positive results. It's for my 2010 race bike I'm currently building.

[cuong-nutz]

I'm pretty sure a few here have. Just remove the whole housing and find a long hose to replace it all. It'll just take a little bit longer for the engine to warm up in the cold. I'd be weary about removing the fan though but that's just me here in hot and humid Houston Texas.

[Triple R]

Originally Posted by cuong-nutz

I'm pretty sure a few here have. Just remove the whole housing and find a long hose to replace it all. It'll just take a little bit longer for the engine to warm up in the cold. I'd be weary about removing the fan though but that's just me here in hot and humid Houston Texas.

That's what I'm expecting too, not a big deal if it takes a bit longer to warm up. As for the fan, a lot of racers take it off around here in California. Thanks for the reply!

[quarterliter]

I wouldn't remove the thermostat. Are you running hot? What is your reasoning behind wanting to remove it?

[Racer x]

I would not do it. There is no good that can come from it. The engine is designed to operate at high temp. But without back pressure you are not sure if the engine has even temperature across the head. To much flow does not allow the water time to soak up heat from the head. And it does not spend enough time in the radiator cooling off.

[Motofool]

Originally Posted by Triple R

Anyone here remove their thermostat? I'm considering it if anyone has had positive results. It's for my 2010 race bike I'm currently building.

If you are racing a 250, you want all the energy that you can pack on those 250 cubic centimeters.

You want your engine to run as hot as parts and oil can stand.

That is the function of the t-stat: to keep an optimum temperature, not just to warm the engine quickly.

Combustion gases in a combustion chamber that reaches 3,500 F push that piston down with much more force than gases that only reach 3,000 F.

Please, read this:
http://faq.ninja250.org/wiki/Cooling_system

Our engines are pneumatic pumps: high temperature means high expansive pressure, which means high force on that connecting rod, which becomes high torque on your rear wheel.

Lower temperatures also mean bigger gap between pistons and cylinders, which mean higher leaks and less compression.

[mgentz]

[alex.s]

i tried it for weight. but its much better with it in. it weighs very little, but has great value

[Somchai]

When you're looking for real positive results you better think about replacing the water pump with an electrical one.

[InvisiBill]

Look into the Thermo-Bob.

With the stock setup, essentially all coolant flow is stopped when the thermostat is closed. Coolant sits in the engine and gets quite hot. Eventually (via conduction and the small bypass hole in the thermostat) the hot coolant gets to the thermostat and causes it to open. Then all the coolant that's been sitting in the radiator getting overly cooled surges into and through the engine, causing the thermostat to close again, and the cycle repeats.

Once it warms up enough this is less of an issue, but it can be brutal on cold starts. On his test KLR with a 160°F thermostat, the stock cooling system never got better than 35°F difference between the engine's coolant input and output on a cool morning; when the thermostat first opened, there was a difference of over 110°F. With the Thermo-Bob installed, the coolant input temp stayed within about 10°F of the output temp most of the time, around 20°F difference at its very worst. When the thermostat first opened, the stock system had output temp swings of over 20°F while the Thermo-Bob was swinging less than 5°F.

The Thermo-Bob adds a bypass, similar to a modern car's cooling system. When the thermostat is closed, the bypass allows coolant to keep flowing through the engine and water pump. When it heats up enough the thermostat opens and lets the hot coolant flow through the radiator to lose some heat. When the coolant cools down again, the thermostat closes and the radiator is blocked off again. This allows the coolant in the engine to stay a more consistent temperature, as it's always flowing, but only going through the radiator when it's too hot. I'm no fluid dynamics expert, but it also seems like the water pump would be happier pushing the coolant through a closed loop rather than churning away against the blockage of the closed thermostat.

The 500's thermostat housing has a separate input from each cylinder, so the add-on Thermo-Bob isn't really compatible with it. I'm working on modding the stock housing to add a bypass - you could try that to avoid adding the commercial Thermo-Bob's extra weight/complexity to a race bike.


Generally speaking, the radiator fan is for providing airflow when there's not enough due to slow road speeds. The fan can actually impede airflow at higher speeds. If your race bike is only stopped for a few minutes at the starting line as opposed to sitting in traffic all day, you might get better results without the fan. The tradeoff is that you'll lose low-speed/stopped cooling ability.

[mgentz]

What about just drilling a hole in the thermostats base plate for a bypass? 1/8" or so should do quite nice.