Overheat or what?

Today I went riding here in SoCal in a place called Moreno Valley. It was about 80F or so and we were on some tight, technical trails and all of the sudden I am blowing A LOT of coolant out of the little weep hole under the impeller cover of the water pump. In fact it drained every last drop out. Luckily I had a fanny pack and enough water to refill.

Now, 2 weeks ago, i blew on of the seals in my water pump and replaced both and they have had 2 rides on them with no problems. Why would all the coolant blow out of that hole and then when I refill the radiator and let the bike cool a bit, it runs fine and no coolant loss? Wierd...

Any help is appreciated!

Anybody? Bueler? :)

I may not be able to answer your question completely, but I can say that I've gotten my bike hot enough a few times to boil out some coolant whilst doing a day of trial riding on my "made for movement" '01 yzf426 and never had any worry of all the coolant coming out. That sounds more like a leak to me than just over-heating? JMO...

[ April 01, 2002: Message edited by: kozmic ]

What's wierd is that after I refilled the radiator, it didn't lose fluid again! You would think if I blew that seal, it would start coming out again. I just don't want to tear into it after I just put i back together...


I already replced both seals 3 weeks ago, so I can't imagine they blew up already??

They were installed as per the shop manual!

It's not your bike over heating, but a leak in your water pump seal. There should be two seals. When the first one leaks the coolant will flow from that weephole. If the second seal fails the coolant will enter the motor(no good). Save your self the trouble and replace both seals(there cheap) and change your oil. Better safe than sorry.


Ther ya go you let that guy Manual at the shop work on it.

My Buck 25

Coolant system has pressure points meaning at specific heat ranges the system will allow coolant out (Better then blowing a radiator), Since there is no collection tank it is va the seep hole.

Seals are made to blow but only under extreame conditions, (I.E. Challager) Ok Bad Example

But they are made to give way in extreame heat. I rode this week end in NoCal Hollister it was hot but not to bad. I noticed when I got home some seeping of coolant and oil from the appropriate places. Also the coolant has a life span of two years period it should be replaced regardless, or if you are really a hard player.....The coolant just maybe getting old and not able to handle the work out any more

I know you said it Leaked all out, but how old was the stuff prior to this ?

[ April 02, 2002: Message edited by: EgoAhole ]


Thanks for the reply. The coolant had maybe 3 hard desert rides. Wide open, sustained speeds at average temps. SoCal high desert is still chilly in the mornings. So, the coolant was in good shape. It was a 70/30 mix of water and rad fluid. I have been great cooling with that mix.

So, basically, you are saying I got the engine damn hot withmy slow-speed hill-climb and the fluid went out the weep hole instead of the radiator overflow?

Maybe it was all the sand I put in the radiator for ballast? :)

Hey Salad,

I have to disagree with the Ahole :D

The weep hole is not going to let water out under heat before the overflow...unless

A. The overflow is blocked.

B. There is a bad seal on the water pump.

A two-smoke buddy of mine has a leaky weep hole (actually I think I might just start calling him that "leaky weep hole" but I digress). He replaced the outer seal on the water pump housing and still, leaky weeper...Then I learned that there are seals on the shaft of the impeller itself and if that is bad it can cause weep seepage.

Anyway, I still say it's probably a bad seal on the water pump and I've heard some say that it's easy to mess one up reassembling...

Anyone else out there with experience to share...

If there's one thing I hate it's a leaky weep hole :)

Good Luck and let us know what the fix is...


Hey EbayThumpbutt


and becouse I am wrong dont make you right :)

So if the seep hole is there for what then ?

A: Looks

B: Yamaha Engineers needed another Hole Somewhere

C: Over Flow

D: Becouse EbayThumButt has no clue

The weep hole is for cry babies like EgoAhole :D

Honesty I was just jabbing at ya for fun and all.

Like I said I had a buddy with this problem and it seemed like a seal issue. And, if you're wrong, and I'm wrong...then what's the problem?

I'll bet that unless there's a problem that hole is supposed to stay dry...

Could be wrong but then...well, 'nuff said.

Don't get your ego confused with your ahole :)



:) Ahh Better

No I have no problem getting ego and ahole confused, Its just so dang hard not having an EGO when I am "RIGHT" all the time :D

No worries all is far in love and war

Haha, maybe my weephole is just really another (ego)ahole. So much talk about holes. :)

Well, I am going to tear it apart tonight and see what's up with it. Maybe my new seal has a tear I didn't see when I installed it. Maybe I need to tear me a new EgoAhole? :D

Thanks guys!

Hey thumpsalad,

I had the same problem after replacing my piston. Some dumb jerk didn't torque my head bolts correctly... :):D So my head-gasket blew and did exactly what you have described. If you can't find the problem anywhere else first, you might give it a look. P.S. Replace the gasket (if that is the problem) with stock Yammaha. You'll be much happier in the long run.

Hope this helps.


Hey Thumpsalad...

Don't forget to let us know what the fix is/was.

Otherwise I will assume I was right and then I don't learn anything...and if I was right then I get to lean into Ego a bit :)

Also, the head gasket sounds like a possibility...that may explain it too.



its been my experience with my truck that that weep hole only weeps when the seals or bearings inside the pump go south. I have overheated my yz400 plenty and never seen that hole leak. Thats why we have radiator caps with a presure rating. to blow instead of the radiator.

Ok, you guys are going to flip...I bring the bike out after washing it and check the rad...still has fluid from the refill I did after the fluid blew out the weep hole.

I decide to fire her up and see if any fluid will come out of the hole again under pressure. I made sure I was ready to kill the motor, just in case.

So, she fires right up and I let it idle since we all know how hot these things get when they just sit there. No leaking. Then go up and down the street a couple times. No leaking.

What the hell?????


The weep hole is also called a "Tell-Tale" hole. Fluid should only leak out of that hole when something with those seals is wrong. It's purpose is to let you know something is wrong. Now in this case, it is more odd than normal (leaks, than doesn't leak). I'm wondering if your crank has a slight vibration that is prematurely wearing your seals out? Also check your pump bearings for abnormal play. Hope this helps

Well, here's what I am going to do about this. I have ordered a new impeller shaft, all seals and a new bearing. I have a wierd feeling about the impeller shaft, but it looked good last time I had it out. Whatever.

These parts aren't expensive, so I might as well replace them to just be sure!

I'll let you all know how it goes!

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