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nitro201

YZ400 & 426 spits out coolant (overheating)

11 posts in this topic

I have a YZ400 bottom end which has a YZ426 Crank, piston, clyinder and head. I've had nothing but problems with this motor overheating from day one. I've replaced the waterpump seals, shaft, bearing, radiator cap and added Engine Ice , filled my coolant one inch below neck. I've blown 2 base gasket and 1 head gasket. I have also tried two different radiator's added a overflow bottle and still overheating. My cylinder on the backside is wearing pretty back so could this motor be getting hot b/c of the oil pump and cause me to blow base, head gasket and then spit out antifreeze. Something is wrong!

PLEASE HELP IF ANYONE HAS ANY INFO......THANKS

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ohh man that kidna scares me. ive just had to replace my water pump seals and shaft and now my radiator cap has gone bad. these 426's build up rediculious pressure in the radiators, i always fill mine up while its running at about 4000-5000 rpms to go ahead and spit the extra pressure out, but it still manages to leak out some.

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You can do a search here on how to make your own overflow tank. That will solve your problem for good. :thumbsup:

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This may sound too simple, but have you tried a different heat range on your radiator cap. If you recall some of the early Kawa and Suz. 250 4 strokes MXers had heating problem that were partially fixed by a different radiator cap. I know you said you replaced yours early on, but was it the same cap or a different one? Try borrowing a cap from a friend a see if a difference is noted..

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This may sound too simple, but have you tried a different heat range on your radiator cap. If you recall some of the early Kawa and Suz. 250 4 strokes MXers had heating problem that were partially fixed by a different radiator cap. I know you said you replaced yours early on, but was it the same cap or a different one? Try borrowing a cap from a friend a see if a difference is noted..

Concur . Use a higher PRESSURE radiator cap . I would find a way to measure the temp too . You may be having pressure (as in too much) and NOT temp issues .

Does any one out there know if the head bolts are "torque to yield" type and/or single use ? ...dont have my manual handy .

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Go out and buy the 1.6 radiator cap(YZFs come stock with 1.1 caps).You can get it at a Kawasaki dealer,they offer this as a stock part.Spend $15 and buy the temperature strips to monitor your temp.I put one on the cylinder,and one on the LH and RH radiators.Did you ever touch the water pump?Try a different cover and impeller.

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Thanks for all the replies but my cylinder is wearing pretty bad and looks like the oil pump might be bad.

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You guys aren't over analyzing this are you?

YZ's do spit and piss a lot if your not moving forward (keeping air going thru the rads).

On a somewhat easy ride (with the wife) I'll have to stop from time to time as she clears an obstacle, and while I'm sitting there waiting (in just a couple of minutes) the bike will leave a nice green spot in the trail...this is normal! Just top her off before you ride with some pre-mixed coolant/water and yer good to go.

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I race quads and this motor never idles except on the line. The antifreeze spits out fluid when I get on it half to 3/4 throttle.

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The antifreeze spits out fluid when I get on it half to 3/4 throttle.

Wow...you got a problem! Sounds like your coolant system is over-pressurizing from compression leaking in. A head gasket or a warped cylinder/head? I see you've gone thru head gaskets, has anyone faced your head or top of the cylinder to make sure there is agood sound flat fit?

Is there oil in your water or water in your oil? Or water coming out the tailpipe (steam)?

You got a 426 crank in a 400 motor....is it bored too, or just stroked? What does that make it, like a 415cc?

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Wow...you got a problem! Sounds like your coolant system is over-pressurizing from compression leaking in. A head gasket or a warped cylinder/head? I see you've gone thru head gaskets, has anyone faced your head or top of the cylinder to make sure there is agood sound flat fit?

Is there oil in your water or water in your oil? Or water coming out the tailpipe (steam)?

You got a 426 crank in a 400 motor....is it bored too, or just stroked? What does that make it, like a 415cc?

Yes last time I took my head and cylinder off, the cylinder was warped a bit and the machine shop had to mill the surface like 5 or 10 thousands because of the motor getting hot. But since I had a bad head gasket I think this is reason why my cylinder was scored. I just want to make sure I get all of bugs figured out this time. No water so far in my oil or oil in my water but it was burning antifreeze and coming out of my tailpipe. So I checked my motor while it was running and found I had a leaking head gasket so I shut the motor down.

I have YZ400 lower bottom end but a YZ426 crank, piston and cylinder so this makes it a 426 but just using the lower half like gears, clutch, cases and etc... from a yz400 thanks

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