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Jonbikes

Coolant leak with start up

26 posts in this topic

Just picked up an 07 yz450 used from a dealership so she's just had her pre flight check. I've only been out on it 3 times (so three cold starts) and the last two of the three the bike has leaked about a tablespoon of coolant onto the ground and then thats it. It only did it with the first start of the day, and the temperature between day one and two dropped quite a bit (first leak was on day two) and then came back up again between days two and three, leaked again on day three. I checked the fluid level today and it is where it should be, perhaps a touch high if anything. It is hard to tell where exactly the leak is coming from due to the skid plate /plastics/little bit of mud but its seemingly coming from the bottom right side of the engine, rite at the front. However, it could be trickling down from god knows where and only visible when it hits the bottom of the bike.

Anyone run into something like this before? I have a feeling its just something to do with the overflow and its being caused by temperature changes (10c above freezing to 5c below freezing) and am expecting it to stop shortly, but I figured I'd ask anyway.

I've let the bike run over dry ground for a while and the drip is only in the first 20 seconds or less of running and ONLY on the first start of the day.

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Sounds like your water pump seal is leaking and it is dripping out of the weep hole in the bottom of the water pump. They always start by losing a few drips on cold start up, and gradually get worse if you ignore it. This is pretty common on bikes once they get a couple years old, but it is easy to fix.

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Is this a gasket or similar on the water pump housing or a rubber seal around a shaft that would likely cause a problem such as this. I have just dug out the old manual and about to tackle some reading as well now that I have somewhere to start.

Thanks!

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It's the rubber seal on the shaft itself. The shaft has 2 seals, one holds the oil in the engine, the other holds the water in the water pump. There is a little space between them with a weep hole in the bottom of the water pump housing. This is so that when one seal leaks the fluid will drip out of that hole and you can tell which seal is failing (and this prevents water and oil from mixing at this part of the engine). The water seal almost always fails first since oil is a better lubricant than antifreeze.

You will have to pull the water pump cover and the outer clutch housing off (which the water pump cover bolts into). The water pump shaft will stay with the outer clutch housing. On the backside of the water pump the shaft will have flat spots to hold it with a wrench, then you can use another wrench to take the nut off on top of the impeller. Once that nut is off the impeller comes off the shaft and you can slide the shaft out. Pop the seal out with a screw driver and push the new seal in. Look over the water pump shaft for any sort of wear, sometimes they get a groove where the seal rubs and this will cause it to start leaking again shortly after you put in the new seal. If there is any wear on the shaft then you should replace that as well. When I did mine I put in a new bearing as well since it is cheap.

Then just put it together like you took it apart, put the shaft back in place, put the impeller on, tighten the nut, and put the clutch housing back on. Make sure when you are putting the clutch housing on that you line the flat of the water pump shaft up to fit in correctly (you'll see what I mean when you look at it).

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Before you get too carried away, your drain hose runs down that side as well (at least mine does).

If you overfill your coolant it will displace itself when it reaches operating temp, in which it will run out the hose and drip a little when you warm your bike up on the stand.

Make sure that you know where it's coming from, if you can't pinpoint the weep hole while the bike is warming up on the stand, then make sure that you are loosing enough coolant in which this is really a problem. You said that your level is good even after the leaks, go for a ride again and check after the bike is cooled down. The level should never drop below the inner core of the rad, if it does then you have an issue.

just my .02 cents.

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Thank's for the replies guys, great info. I'm going to wash the bike next time I have a chance and then get a better look at things. It's such a small amount that it would have to do it 100 times to be a danger to my coolant level, but its kind of annoying.

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It's true that the pressure will push out water through the overflow if the radiator is overfilled, but it will only do it the first time you start it after filling the radiator (andit typically takes a minute to build up enough pressure to push fluid out). If it is leaking right when you start it, and it is leaking on every cold start and you aren't adding fluid then it is almost always the water pump seal. Just look for where it is coming out next time to know for sure, it will be easy to tell which it is if you look right at the bottom of the water pump and then look at the overflow hose.

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Before you get too carried away, your drain hose runs down that side as well (at least mine does).

Make sure that you know where it's coming from

appears brentn has a tad more sense than alot of folks :thumbsup:. blindly tearing stuff apart is very foolish

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It's true that the pressure will push out water through the overflow if the radiator is overfilled, but it will only do it the first time you start it after filling the radiator (andit typically takes a minute to build up enough pressure to push fluid out). If it is leaking right when you start it, and it is leaking on every cold start and you aren't adding fluid then it is almost always the water pump seal. Just look for where it is coming out next time to know for sure, it will be easy to tell which it is if you look right at the bottom of the water pump and then look at the overflow hose.

Yes forgot to clarify this!!! :thumbsup:

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Sadly I checked on the drain hose and it runs no where near the leak so that's out of the picture, and I thought I was quite clear on it only leaking with a cold start (perhaps that was meant for the guy that replied to the thread??). I've got the bike all washed up now, will be taking a more comprehensive look at the situation after work today.

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Just picked up an 07 yz450 used from a dealership so she's just had her pre flight check. I've only been out on it 3 times (so three cold starts) and the last two of the three the bike has leaked about a tablespoon of coolant onto the ground and then thats it. It only did it with the first start of the day, and the temperature between day one and two dropped quite a bit (first leak was on day two) and then came back up again between days two and three, leaked again on day three. I checked the fluid level today and it is where it should be, perhaps a touch high if anything. It is hard to tell where exactly the leak is coming from due to the skid plate /plastics/little bit of mud but its seemingly coming from the bottom right side of the engine, rite at the front. However, it could be trickling down from god knows where and only visible when it hits the bottom of the bike.

Anyone run into something like this before? I have a feeling its just something to do with the overflow and its being caused by temperature changes (10c above freezing to 5c below freezing) and am expecting it to stop shortly, but I figured I'd ask anyway.

I've let the bike run over dry ground for a while and the drip is only in the first 20 seconds or less of running and ONLY on the first start of the day.

I had the same issue when my '07 was brand new. My bike would only drip a little antifreeze out the weep hole when the temps were very cold outside and the engine was cold. Once the engine was warm, I had no leakage. I eventually changed the w/p shaft seals, and that was the end of the issue. My bike's been fine ever since.

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I've cleaned the bike and removed the plastic guard from the pump area. The coolant does indeed seem to be coming from the weep hole on the pump but the amount has remained consistant. I wouldn't worry about it if I had a way to monitor the temperature or coolant level, but I have no way to tell if it decides to dump 3/4 of the coolant mid lap or something at the track. I'd hate to cook my new bike because of something stupid like this. Going to see if the dealer has at least the seals in stock, and if they have bearings and or shaft I will just change everything all in one go.

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Best bet is to change the lot if you can. My last bike was a Honda , of similar age to yours. It weeped a bit on startup, and like you, any water loss that wasnt out of the overflow worried me because you don't know how much you have lost/are losing.

I first changed the seal, and it came back after a couple of rides, so I changed the lot and it was fine afterwards. The old shaft looked fairly good, but was obviously causing the issue.

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I have a sneaking suspicion that I may be able to track down the seal but nothing else so I might be stuck with a temp fix while the rest of the parts are on order. See what happens today when I go to the dealership.

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My thoughts are the rubber content of the seals might have been a bit too hard, thus allowing some "cold" leakage until the seal warmed up and created a positive seal around the perimeter of the shaft ?

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Called the dealer, sure enough they had everything in stock so I picked up both seals, the bearing, o ring gasket for the cover, and the shaft. Tore into it tonight and sure enough the shaft was completely worn out where the water seal rides and was just starting to show signs of wear where the oil seal sits. The bearing was in perfect working condition so I will save the new bearing for next time. Hopefully this problem is solved and will stay that way for a long time.

Put it all back together and dropped some oil and coolant into er but didnt have time/to late to start the bike in town so I'll top it up tomorrow and then hopefully get out friday sometime.

Thanks for all the help!

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I've got a '98 yz400f converted to a 426 that had a leak out of the weep hole and it was obvious once the back was started and warming up you could see it pushing water out of the hole. I replaced the impeller shaft and seals and haven't had a problem since. I do get coolant coming from the overflow hose onto the ground, like a drip that drives me crazy. I just got back from baja where on the first day after logging over 200 miles I was down about a half a quart of coolant. The bike doesn't have a reservoir and I'm not sure why it would be pushing coolant out the overflow. Since we're on the subject does anyone have any feedback why I'm getting a drip out of the overflow? I'm filling it to the top of the radiator so I'm probably overfilling it but that still seems like to much coolant to be dropping.

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I believe I mentioned it earlier, but if you overfill coolant you'll get some drippage, but only usually just a bit at first. It will stop once enough has come out.

Do you have any kind of instrumentation to show the temps of the bike while you are riding it? If it's going over 100C then that could be your problem, you'll need to get yourself a catch can. A trailtech is awesome for this cause it will log maximum speed, temp and rpm so you can look back and see how hot the engine did get when you were too busy to look at the gauge.

If not, and the temps are below boiling, it might be worth while to get a new rad cap, and inspect the flange where the cap sits and make sure its clean and relatively straight and flush.

If that does not cure the issue, then you may have a slightly blown head gasket, just small enough of a breech in which your not overheating right away, but your losing all your coolant.

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No I don't have anything to check the temp. but I replaced the cap with a new High Pressure cap. I'm thinking about going with the reservoir idea and see if that works. I can't say I'm too familiar with the temperature affect on the coolant, from what I'm deciphering from your comments is that once the coolant reaches a certain temp. it will look to replace pressure and exit the overflow tube and the traitech would measure and confirm this.

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