WR 400 Boiling Over

I have a 98 WR 400. I am overheating on slower rides where I am boiling out half of my coolant. On faster rides it is okay but it still gets really hot and boils out more than I would like it to. When it is cool and I take the cap off and start it the coolant is flowing but I don't know if it's flowing rapidly enough. Can anyone tell me how fast the flow should be. I know that it is hard to describe! I am wondering if my water pump is working correctly

My 99 WR has been boiling at low speed since new, even at -30. I hear some riders install small computer fans to help cool the rads in the slow stuff.

My tank has been removed? As far as the engine ice it boils out also. At $16 a bottle that makes me mad. I read the other post on this but no real answers except for the fan. i know a few guys who have DRZ 400's and they put fans on them and they are awsome. They really hold up also but DRZ's dont run as hot as the WR's. I might try to configure a mounting system for it.

too lean....too hot ??

My tank has been removed?

There is your problem. That tank is there for a reason. To catch the coolant as it overheats. When the bike cools down it will take it back in from the catch tank. Put the catch tank back on. Problem solved.

My yz400 overheats on slow trails. My buddies wr400 doesn't. Differance?? catch tank. Wr has one my yz dosn't. That and the wr has bigger radiators. :thumbsup:

Does the cooling down cause a vacuum that sucks the coolant back into the radiator? If so how can it cool down when racing in an Enduro where you don't stop long enough. The main problem is the overheating not where the coolant is going. If I am missing something then please explain?? :thumbsup::awww::lol:

I have my overflow tank still onboard. It fills fast when the bike gets hot and then dumps the coolant. It may buy you an extra minute over a bike with no overflow. If you're stuck in a hole for a few minutes you're gonna boil over. My bike blows her wad every time without airflow over the rads, no matter how cold out it is. I pack the rads with snow to keep 'em cool till I get unstuck.


I removed my overflow bottle on my 98 WR and replaced the stock rad cap with one from a KX500 (1.6 vs 1.1) and have NEVER lost coolant, and have NEVER had a problem with too much pressure. I've even got a banged up left rad and still no leaks or boil overs. I acquired a YZ400 (98 as well) last year and I'm not sure who says the WR rads are bigger. I can swap the rads from bike to bike and they look exactly the same to me. My big question would be....HOW LONG HAS IT BEEN SINCE YOU REPLACED YOUR CAP?? If it's got a weak spring, you'll lose coolant LONG before it's designed temperature.

Good point :awww: now why didn't I think of that :thumbsup:. Less pressure boils sooner and leaks out. I'm ordering a new cap today. Mine is original. Thanks Butta.

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