YZF overheating

bry

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#1
I have a 98 YZ 400 its the first bike I've ever owned, and I don't know anything about the stupid thing. Anyway i was riding last weekend and the coolant was boiling out of the overflow along with tons of steam. I wasnt riding the bike hard at all i was just crusing around in third gear. Anyone got a idea of what could be wrong? The only thing I could think of was that i was going too slow to get enough air though the radiator. Please help.:(
 
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#2
That happened to me this weekend on my 99 WR. I was riding with a slow group in 1st gear almost the whole time. I stopped to pick a quad off a girl who got stuck under it and noticed the green stuff dripping form the overflow tank. It took about 3 mins to let all the steam out of the tanks before I could add water. Once the coolant was mixed with water it did not over heat again. I dont think these bikes like %100 anti freeze in them, and that looks like what was in it. I am going to drain the whole thing bcause I used tap water out of my camel back (thank goodness for that thing!!!!) and tap water can have miniirals in it that will wipe out the seals and eat at the aluminum. I will be going 50 / 50 water and antifreeze, maybe peak brand and I will be using some water wetter in it. This is a heat exchange catalist that makes the coolant more efficiant. I belive the YZ have smaller rads than the WR and I dont think they have over flow tanks under the left side number plate either. If it still boils over with the above mentiond coolant mixture in the slow stuff, you may want to look into some 2001 speck WR radiators for it. I belive the 01s have added cores in the rads.
 
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#3
I also own a '98 YZF. I noticed a small amount of boil over so I picked up a higher pressure radiator cap (picked it up at a Kawi store, stock cap for a KX500).

Even with the higher pressure cap no negative effects on the rads or hoses. I also picked up the Boyesen Impeller and I run the Water Wetter product with some Honda premix coolant.

Each of the steps above is suppose to add 5-10 degrees to the boil point. Take your pick or try em all.

Mike
 

Thump

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#4
Bry, the 98' 400 had impeller problems if I remember correctly, they changed it in 99' to help cure the over heating. I live in Texas and ride in the middle of the day in August heat on a 99' 400 (now a 417) I sometimes had an occasional overheat but have not had any since I switched to Mobil 1 15w50. I run 60/40 distilled water/antifreeze. I think the oil made a big difference, I would try that first then consider an impeller change. I "think" Boysen makes the impeller.
 
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#5
My buddy has a 426 and I have a KX250. We do lots of tight woods riding. If the temperatures are above 50' F we usually will switch to distilled water and water wetter. This works great for us. Just make sure you switch back to 50/50 mix before winter. That is if you live near cold climates.
 

bry

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#6
Thanks for the input guys I'll let you know how it works out next week. thanks again!:)
 
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#7
Boyesen does make the Impeller, I think it is around $53. Availble via most catalogs. Easy to change, comes with gasket, etc.

Mike
 
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#8
the rad cap will go bad over time try that first and you also might check the water pump impeller if that doesn't work.
 
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#9
The yzf400s had small radiators for the bike. They upgraded the size of them with the 426s. You can get some IMS radiators that are oversized for the bike for less than OEM 426 units.

Inspect the water pump for any damage.

I also had a friend that has a 400 and the bike always overheated. When the motor blew, he took off all the external oil lines and found one of the hollow dowl pins (designed for oil to flow through) was crushed by incorrect installation at the factory. I would suggest that you inspect all of them! Lack of oil to any part of the engine would definately overheat the motor.

Myself in the 426 I run 1 bottle of waterwetter (redline) and fill the rest with dexcool (the red antifreeze). The dexcool because it has no silicates in it. Never had it come close to overheating.
 
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#11
I was curious if Royal Purple coolant additive would also work, I am getting a 98 YZ 400f in a few days. The owner also put one 426 rad on there after a crash.