Can anyone tell me what the fan is for on the back side of the radiator, because i have never heard it come on. And even more important does this bike need it at all.( the 300r doesn't have one) Reason: fitting the IMS tank also drop some more weight. I have been trying to figure it out and i have had no luck. Between all the mechanically incline people on this forum I know someone has the answer. Thanks for your help guy's I value all your information more than talking to any of the know it all service guy's at the local shops.

 

Protection! A KLX300 doesn't sit on a hot freeway@5mph in the summer, my 250 will.

 

tony so your saying as long as im not in stop and go traffic I dont need it?

 

I was out today on the KLX 250S brush whacking through some particularly tenacious terrain - old clear cut with brambles and small logs, getting tangled up and having maneuver every hard earned foot of progress. I noticed the fan kicked on several times navigating this tough terrain. I wasn't anywhere close to traffic nor even a road for that matter.

 

but you ride the same terain on the klx 300r and it doesn't have one so weather your doing full out motocross style riding or single track inch earned riding do you really need the fan? And better yet do you think the bike will over heat? These may sound like stupid questions but it comes douwn to dropping wieght and fitting that IMS tank without messing with the integrity of the tank.

 

I can't answer that. My feeling is that it is probably required, presumably designed into the cooling system by Kawasaki engineers to solve a specific problem that they saw, otherwise, why would they add it since it adds cost to the bike and makes manufacturing and part sourcing a bit more complex? If the fan is in the way of the larger tank, perhaps it (the fan) can be moved rather than removed completely? Or perhaps a smaller, higher RPM fan with the same CFM flow, can be installed instead? BTW, it was pretty cool out when my fan was turning on this afternoon - down in the 40's here.

 

I rode HARD today on some very knarly single track (big a$$ rocks and SLOW going. Not one fan run the entire day. Of course, it was 55 degrees.

I will be in stop/go traffic in 110F heat this summer so keeping some kind of fan is likely going to be required.

I have a theory on the fan: The 250S includes an air injection system (air valve in Kawi speak). This is designed to inject air into the exhaust port as the exhaust pulse is moving out toward the header. The purpose is to allow a bit more left over fuel to burn. However, this significantly increases exhaust gas temp (notice your head pipe blued in the first 5 miles?). This is a common EPA measure on carb bikes but it also increases head temp. This is one of the reasons I removed it.

Another factor is the 250S is set from the factory to run leaner than the 300R. That too means more heat.

With the air valve gone and the jetting I have, I'm betting the bike's running cooler than stock.

When I fit the IMS tank, I'm going fit a low profile fan just to be safe but I bet it's hardly ever required.

 

Good post todd! Before I had read it I just spent four hours researching parts diagrams from 96' klx 250 06' klx 250 and 06' klx 300. Mainly looking at cooling systems, carb difference's, water pumps, air intakes, and shrouds. I printed out every single diagram and compaired everything. The only rock solid thing I could come up with was something close to what you said. The EPA requirments force the lean jetting on all kawa road bikes including dual sports. All of kawa's dual sports going back into the 90's have fans due to pleasing the EPA. But on the other hand none of there enduro or motocross bikes have fans due to weight and they normally run much richer. So like you said todd if you re-jet the carb you should be fine with out the fan, so as long as your not in 100 degree weather going 2 MPH up a hill for an hour or same goes sitting in stop and go traffic. But hey if your in stop and go, grow some ***** and split the lanes, dont be paranoid highway patrol usually doesn't even see you and if they do they usually dont even bother( If your in a state that lane splitting is illigal). Sorry got of track so in conclusion Im taking of the fan to fit the IMS tank. If I burn up Oh well! thats what they made JBweld for.

 

After all my psyco babble more proof of a fan that doesn't need to be there. At least this is good enough for me. the 2003 klx 400sr(dual sport)
has a fan behind the rad. The 2003 klx 400r( offroad edition) does not. So what does this info tell me the fan is useless if your running rich wich most of the people on this forum are. Also the 400sr ran a mikuni bsr 36 carb, And the 400r ran the keihin fcr 39 wich looks to be a racing carb. I don't know enough about carbs to really get into the difference between the two. Im just trying to put the info out there. I tried to do my homework on this one. But I still could be wrong. If anyone else has anymore information on the subject please post. I am not a pro I just like to take things apart.

 

My KLR250 has a temp guage, riding in deep sand was the only time my fan ever came on (several times) and it bought the temp down from the top of the guage to the middle where it normally is.