I'm pulling my hair out: WR boils over even on the highway...

Ok, so it's now clear that my bike is boiling over ALL the time. Today it boiled over even after 15-20 mins of riding at speed (between 30-105km/h). No stop and go, slow first or second gear technical riding and I wasn't riding the clutch... 


Two-three weeks ago, I assumed I had a faulty radiator cap because the bike was overheating a lot and coolant wasn't being sucked back in (or it was, but took like 40 mins). The bike used to only boil over in technical stuff when I was riding the clutch, and after waiting 5-10 mins the coolant would get sucked back in. That's why I assumed the radiator cap was busted. After looking at other rad caps and comparing them to mine (with rubber "lips" overextending vs ones that are flush), I was sure this was the culprit. 




However, that still doesn't explain why the bike would boil over under such riding circumstances. Plenty of guys ride in the desert and from I can tell, this isn't normal. So anyways, today I pulled the coolant lines and lo and behold, there was a leak. So I then assumed the air leak is what made the bike heat up so quickly and prevented the coolant from coming back. It would certainly prevent coolant from going back, but would it affect how fast the bike boils over? ANYWAYS, right after changing the lines I went riding for another 40km and even with the new lines, the bike boiled over after 15km of quick-paced riding (50-80km/h). What the hell? 



What should be my next move? So far this is what I'm thinking:

1-Head gasket? I changed my head gasket around 2 months ago after a big failure (blown near the pipe header). Perhaps I messed it up and the new one isn't seated properly? No obvious signs of a faulty gasket or leak, but could this be the culprit of the overheating? I think this is my main target at the moment... 


2-Jetting? Maybe a clogged jet or bike is too lean? To be honest, I have NO idea what my jets are. I'm at sea level with ~40C ambient temperature (105F). However, the bike runs beautifully both at idle and full throttle so I don't want to fix something that isn't broken. All I need is a bit of choke when cold and then perfect idling, and strong power throughout. 


3- I recently changed my ignition coil because the bike wouldn't start (started by cleaning the starter, but still had problems. Now it starts fine). I think it's from a 250F. Would that affect anything? However, the constant boiling over started being a problem BEFORE I changed the ignition coil, so I doubt that's the cause. I'm just putting it out there. 


4-I changed the waterpump bearing and gasket recently. No signs of a new leak. I'll check the oil, but I don't think it's an issue anymore. Impeller maybe isn't working properly? Take off the hose from the waterpump and check if it's circulating? 



Other leads? Busted rads? No leaks that I can see... Timing chain? I'm really at a loss and this is starting to frustrate me and making me loose faith in the bike. I've heard on some Aussie forums about putting heat tape on the rad near the header to reduce boiling over. Still, there must be some deeper issue here, as I'm boiling over no matter how I ride. Not normal (or is it?). 

Edited by Bitteeinbit

Mine runs too cool at speed, so I suspect that your problems aren't normal (even if the weather is 40F warmer there than here - I can comfortably put my hand on the head after riding for a while). 


You can get kits to test coolant for exhaust gasses. That kinda sounds like your problem to me, and it will keep the coolant from being sucked back in. 


If it's running well, I wouldn't expect jetting or timing to do that... but I haven't done enough with mine to say that for sure. 


Not a bad idea to verify that the water pump is pumping but I highly doubt that's the problem if you can ride it 15km. 


Depending on what you use as coolant it's possible that the radiators are all clogged up with gunk/mineral deposits, that can make them less effective.

A boil over from a bad cap is not from a, "Boil Over" it is lost of fluid from the pressure due to expansion of the coolant heat.  That may sound like semantics but there is a difference.


This is what I would do:


1.  Replace the cap.  They are cheap.

2. Check all your radiator overflow hoses all the way back to the reserve bottle making sure there is no kinks.

3. Run your bike with the cap off and see if you got good flow when revving the bike to make sure your water pump I working.

4.  You can rent a radiator pressure test kit from the local Auto parts store.  This will check to see if you have a leak in the system, including the gaskets.

5. If these things are all good, then pull your radiators off and checked them for flow.  However, unless you have dumped crap in them, they shouldn't be clogged up.


All the other stuff is not going to cause an over heating issue.  WR's are not know to overheat like other bikes.

Hopefully your not running straight water. You need at least 50-50 in there and remember the radiator fluid will expand and push some out when heated.

Your old radiator cap looks like crap.  The cap looks like it has rust on it.  Rust in the system??  Doubt it but just flush the system completely, put in some new coolant or engine ice, make sure you don't have any air pockets and ride it like you stole it.

Flush the system and inspect

Your radiators are probably corroded and done, due to someone using tap water in the radiators...

Not a overheat problem but my 2007 wr450, if I put a little coolant in the recovery tank and go ride it comes back empty. The radiators stay full. If I do not put coolant in the tank and ride the radiators still stay full. Any ideas why it drains the recovery tank?

Thanks guys

You got a leak in your recovery tank or a bad line leading to it.

I had an Aprilia that had a bad cap.  I only picked it up when I fixed the head gasket it caused to blow from overheating.

Sorry for the late reply. First off, thanks for taking the time to answer and giving me all the great advice. Turns out it was a busted head gasket. I also changed the radiator cap just in case and so far no boil overs. I'm taking the bike for a proper 1-2 hour off-road spin tomorrow to make sure it's all good. I also managed to find some distilled water (hard to find here) and flushed my system and replaced it with 50-50. I did notice that now the bike seems to have trouble starting again and the power was inconsistent (on and off), so I suspect the guys fiddled with the jetting a bit. I'll have a look at that tomorrow as well. Maybe they accidentally leaned me out a bit, which might account for the harder hot starting and "off/bumpy" acceleration. I do think my idle is a bit low as my headlight fades a bit unless I rev whereas this was never the case before (plus the sound of course). 


So as usual, fix one problem, add another... *sigh* Hopefully I get this one sorted out cheaply/easily. At least I'm not boiling over I guess!

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