Overheat in 30 sec

4 replies to this topic
  • saca

Posted January 04, 2009 - 06:41 PM


Hi! My friend have a 99'yz400 I think same as 00'426. After it starts up 30-60 sec and a pipe red hot and stop running there is no idle. The radiator is clean,The water pump is working. We run water down the hose from the left side of the radiator top hose and water come thru the water pump. Sothe radiator and hose are not clogged. Radiator cap is good.
Any idea? Thanks! HAPPY NEW YEAR!:thinking: :smirk: :smirk:

  • gtxkid

Posted January 04, 2009 - 07:00 PM


Maybe someone else will chime in here but something doesn't sound good.
I do not know how the hose's hook up but maybe there criss crossed.
Something strange.

Pipe red hot, have you checked the spark plug (Jeting)
Do you have a manual for it.

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  • BC3

Posted January 05, 2009 - 11:27 AM


[COLOR="Blue"]There isn't enough info for me to give you the answer you want so lets start from the beginning...What changed from the time the bike ran normally to how it is now? Did it start doing this "Just all of a sudden"
Typically a water cooled engine won't over heat and stop unless the water is boiling hot and over flowing out the over flow hose...(Very hot)
So I'm thinking the water cooling system isn't your problem.
Ignition timing can cause an over heating problem also but usually the water again will be boiling (overflow tube) From what you have said I feel you have a tight exhaust valve.......Does it start easy and take throttle or does it try to die like it's starving for fuel? You need to answer some of these questions first .....Remember that the new Titanium head pipes will glow red normally so don't confuse that with over heating.... [/COLOR]

  • Yamahondaha

Posted August 28, 2009 - 12:42 PM


I have been searching for possible solutions to my 99 YZ400 overheating trouble and wondered why this tread went dead?

I will not try to pick up where saca left off, in my case I bought my bike in a basket and reassembled it reusing the original head gasket (I wonder if that could cause overheating).

It had a pair of hot cams in it that were sent back for evaluation and HC sent them back to me with a clean bill of health.

I have checked the ignition timing with a timing light and it was spot on and steady.

I replaced the radiator cap with a new one, checked the water pump impeller and radiators for any signs of abnormality but found none.

My question is this:

Could the Hot Cams cause a well behaved YZ400 to puke coolant after only a few minutes of power-band riding or would a bad head gasket be more suspect?

Thanx in advance to anyone that replies with helpfull advice :ride:

  • 642MX

Posted August 28, 2009 - 04:25 PM


What's 'power-band' riding?....

Here is the deal on YZF's over heating.... They like air flow and lots of it. Idling in the garage will heat them up fast..... they are meant to run. They only need a minute or two at the most to warm up. Glowing headers are normal.

YZF's also don't like their radiators filled to the top. Only put enough coolant in to cover the core. If you over fill it, they tend to spit it back out (which really doesn't hurt anything).

Hot Cams will make no noticeable difference in how hot they get.

And NEVER reuse a head gasket, your asking for trouble if you do.

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