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450 cooling, radiator and boil bottle

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I was preping my bike properly for a change for a fun ride when i noticed the boil bottle completely empty on my 450x. I have been riding like this for 2 months no problem. is it suppose to be empty or should it have at least some water in? Secondly how does the coolant flow through the radiators when it leaves the motor? does it flow into one radiator then the other or is it split into both radiators? I would like to fit a small rad fan and want to know which side is best. it gets to around 36 deg celcius here in summer and would like to keep the bike cooled down even tho im yet to experience an overheating issue. any other tips to keep the temp down on some tight slow wobbly stuff? the bike has 13/51 gearing

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There should be some coolant in the overflow bottle. There should be markings on it showing the high and low level. Most are markings are about 1/3 to 1/2 full.


The coolant on my KLX450R leaves the head and splits at a "Y" going to the top of each radiator and then out the bottom to a "Y" which goes to the water pump. The water pump then circulates the coolant into the water jacket and back out of the head.


If you install a fan, just put it wherever it will fit. I am really not sure I would go to the trouble though if you have yet to over heat.


But I also question if you have really over heated or not since your overflow tank is dry. I would think the capacity of your overflow tank would be enough that even if you did boil over to the point it was spilling out of your overflow tank, it would have more than enough to fill the radiators back up as it is drawn back in during the cool down still leaving a visible amount in the overflow tank.

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The flow is out of the water pipe at the front left of the cylinder head, up to the top coolant pipe on the left side radiator, from here the coolant stream splits, some of the coolant cascades down to the coolant pipe at the bottom right of the left radiator and into the water pump and the rest of the coolant stream flows through the top hose connecting the two radiators and into the right radiator which cascades down to the coolant exit pipe on the bottom of the right radiator and into the water pump.


The OEM Honda fan attaches to the three mount points at the top of the right radiator, or if you have removed your smog equipment, one can also be mounted on the bottom of the right radiator. You can also remove the plug at the bottom of the right radiator and install the CRF250X thermo fan switch and wire that in to the fan circuit so the fan will come on automatically. You can also run a manual fan switch by itself, or run it in series with the OEM switch. Based upon the price, it appears that Honda is awfully proud of their fan kit....I suggest that you look at the SPAL fans, as they are about one third the cost of the OEM fan.


Last thing to consider is where to tap into the harness to obtain power for the fan. I believe there is an open connector on the stock harness that can be utilized to power the fan, but you will have to fabricate a subharness to complete the wiring. If you have a Vancouver Supermoto wiring harness, the harness comes with a provision for powering a fan.


A more complete description of the OEM fan kit installation can be located here:




This might also help you with wiring a SPAL fan.


The SPAL fan and associated accessories can be located here:



Edited by Norcalboy561

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