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Air Temp Effects?

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Hey Tim,


I raced my Moriwaki yesterday (CRF250X motor). It was COLD out, about 30 degrees F in the morning and around 45 or so by race time. My bike normally warms up to 80C or higher, and it got up to 67 or so in the pits, but once I started riding the temp reading dropped to around 48 degrees C from the cold air.


I've seen people tape up part of the radiator (on go-karts, anyway) on cold days to keep the engine temp higher - is that something I should be doing on my bike when it is cold? It seemed to run fine, maybe a bit down on power at low RPM, but otherwise OK. Does the radiator temp matter for engine performance?


Anything else I should be aware of on particularly hot or cold days, should I be adjusting anything?

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Brrrr Laura...that sounds pretty cold. :/


Running your bike on the colder side will definitely have some side effects. Below are two of the major ones that pop in my head...


1. Colder temperatures will make all of the lubricating fluids "thicker", which will steal some horsepower. The engine has to use more power to push the thicker oil around. I have seen this A LOT when dynoing bikes up here in Montana. When I'm making dynoruns on our cold Harley Road King, I've seen the power increase as much as 10 horsepower as the bike is warming up.


2. One of the other side effects of running an engine on the colder side is the effect it has on fuel vaporization. When the fuel and air are making their way toward the combustion chamber, the fuel vaporizes on all the hot engine parts that it is passing by. This vaporization is a good thing because the smaller fuel vapor particles are easier to ignite when the spark plug fires. If the engine parts are cold, the fuel doesn't vaporize as much making it slightly harder to ignite.


Covering up your radiator will definitely help keep your bike warmer. You will probably want to experiment with how much needs to be covered to hold the temperature you want. I agree with ktk_ace on the temperature range. Shoot for running with a radiator temperature in the range of 80-100 degrees C(176-212 degrees F).


Hope that helps :)

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That helps a whole lot, thanks! So... Is there a certain part of the radiator that is better to tape, like the top or bottom? Or just whatever is easiest to reach?


It was cold enough that I had to run the bike about every 30 minutes to keep it warmed up enough that it would START reliably! I may invest in some sort of cover for it so it doesn't cool down so fast. Or stay home when it is this darn cold. ;)


BTW, the BMW S1000rr fired right up first thing in the morning, and once it was warmed up it stayed warm, I guess those are designed for a bit broader range of riding conditions! :)

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Laura, your last post actually illustrates a good point.


The CRF250X motor you are using in your Moriwaki probably DOESN'T have a thermostat. The S1000RR's DO have a thermostat.


You may already know this but...

The thermostat is basically a valve that allows the fluid from the radiator to flow to and from the engine. When the motor is cold, the thermostat stays closed which blocks the cooler coolant fluid of the radiator from getting to the engine. At some point the coolant in the engine will heat up and thermostat will open. Once this happens, the colder coolant fluid from the radiator will make its way to the engine to cool it down. So basically the thermostat makes it possible to hold the coolant in the engine at a minimum temperature.


Make sense?


I haven't seen your Moriwaki, so I'm not real sure what to tell you as far as how to block off the radiator. You'll just have to do some experimenting to see what works best. ;)

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