Newbie Question

7 replies to this topic
  • steverox

Posted August 16, 2002 - 06:27 AM


O.K. here I go again with a newbie question...I'm sure this will get me some more smart ass
I just raced my first MX this week and while I was on the line I looked down and noticed my '00 426 blowing coolant out the overflow like crazy. I use a 50/50 mix with water wetter (1 oz.) and my radiator cap is the stock 1.1. I always fill the radiator to the neck when it's cold. My friend has a '98 400 and he has no problems with this at all. Just wondering what I'm doing wrong. Would a higher pressure cap help? If so, where can you purchase one? Are there any disadvantages to having a higher pressure cap? Any other suggestions would be appreciated. Thanks!

  • beezer

Posted August 16, 2002 - 06:38 AM


Sorry Steverox we are way to busy name calling to answer any question about YZ's :)

The cold coolant expands when heated and blows out the overflow. Thats why many bikes have a puke tank, when the bike cools it pulls coolant back in.

Don't fill it all the way up when it's cold.

  • sirthumpalot

Posted August 16, 2002 - 07:06 AM


If you fill it to the top then you will loose some no matter what. However it should not be blowing out non-stop. If this is happening then you've probably overheated (boiling coolant). In this case maybe wait a little longer before starting the bike on the line so it doesn't run in one place quite so long. Also keep the revving to a minimum, just let it idle and it won't heat up quite so fast.

  • Hick

Posted August 16, 2002 - 07:07 AM


I wouldn't worry about it for MX. For woods riding you may consider a higher pressure cap, 1.4 is the only other kind I've found, they come on every KX I've ever seen. I've tried to find a 1.2 or 1.3 w/ zero luck...

A number of people here use them I'm sure, but I would be a little worried about increasing the pressure in the entire system. To a certain extent I'd rather lose some coolant out the overflow than risk blowing a seal or o-ring somewhere.

Also, ditto what Beezer said. Not about flame wars, but about overfilling. In my experience anything above about the halfway point of the top tank just ends up on the ground.

FYI 1.1 Atms equals about 16 psi, 1.4 is almost 21 psi. According to Microsoft Excel, anyway…

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  • Shawn_Mc

Posted August 16, 2002 - 07:22 AM


Ya, dont bother filling it up clear to the neck, it just blows out.

  • BigDesto

Posted August 16, 2002 - 11:03 AM


Make sure that it circulating? water pump?????

  • yznvegas

Posted August 16, 2002 - 12:10 PM


Just like the earlier posters stated, don't fill it up to the top when cold. If you want to make sure it's full you can run it with the cap off just idling and get and get all the air bubbles out and then top it off.

How fast were you going when it started puking?

If you aren't going at least 20-25 mph on a hot day I think it will overheat.

The water-wetter is good stuff and I have used it on 115 degree days out here.

  • bbeakley

Posted August 18, 2002 - 11:05 AM


4 strokes seem to run hotter than the 2 strokes so if you were up there for a few minutes idling and rapping the engine up to get their attention, that probably caused it to overheat (at nighttime the header pipe glows when you idle for a while, it's pretty cool to see). If I'm not mistaken the book says to only fill until all the fins are submersed when cold, no more. I could be wrong though, been drunk and slept since I read that...

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