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bigmack91

Radiator over pressure ?

14 posts in this topic

I have a '99 yz400f. I just recently replaced the top-end , and put 426 rads on it. Rads will not hold coolant. Filled them, jumped on as soon as I started it and took off after 30 seconds coolant was blowing out of the pressure relief hose when on the throttle. Also have a slow drip coming from a small hole in the right right side of the casing, it's a perfect circle and looks as if it's supposed to be there. Could it be a tadle-tale like what u see on a vehicle for a bad water pump seal?

Bike is running a tad lean. Shouldn't effect the coolant that much, Right ?

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Hey why did you leave he chat room? But anyways sound like you have clogged rads and they are over heating

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i know its a no brainer, but make sure u torque the bolts correctly when ya throw another gasket in there... that seemed to be my issue a few years ago when i ran into the same problem on my 250f.

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Just, put a new head gasket on 3 weeks ago, and I torqued them to specs ? How certain are y'all on that ? And does anybody know why there would be a 1mm hole in the bottom of the gear case on the right side... Weep hole ?

2nd that bad head gasket.

had the same problem, head gasket.

Sounds like a head gasket leaking compression into coolant passage.

Coolant slowly drips out until the rads are empty !

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Did u measure head bolts? Possibility they have stretched, and if they're in a blind hole, can bottom and not clamp head tight. Not sure on this model as I havent had pleasure of working one, but if it has studs ignore the above. Could be faulty gasket. If it didn't do it before, has to be something that changed.

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Did not measure head bolts, was not doing it before, how accurate do the torque specs have to be my TQ wrench is a bit old. Will it mess anything up if i plug this hole ?-RTV

That is weep hole. Over pressure could've damaged seal.

Did u measure head bolts? Possibility they have stretched, and if they're in a blind hole, can bottom and not clamp head tight. Not sure on this model as I havent had pleasure of working one, but if it has studs ignore the above. Could be faulty gasket. If it didn't do it before, has to be something that changed.

Weep hole leak... Easy fix ??

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Do not plug hole, there Is a write up on here somewhere about changing that seal. Not really that hard, just have to take water pump cover andlarge clutch cover to do it correctly. I have cheated by removing water pump cover, then the impeller, then placed air nozle in weep hole and blowing the seal out. The risk is turning the impeller and breaking the shaft as sometimes they van be stuck. I think u should buy a compression tester, turn to tdc, charge cylinder with air and look for bubbles in radiator. If bubbles, looks like head gasket or cracked head or cylinder.

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Do not plug hole, there Is a write up on here somewhere about changing that seal. Not really that hard, just have to take water pump cover andlarge clutch cover to do it correctly. I have cheated by removing water pump cover, then the impeller, then placed air nozle in weep hole and blowing the seal out. The risk is turning the impeller and breaking the shaft as sometimes they van be stuck. I think u should buy a compression tester, turn to tdc, charge cylinder with air and look for bubbles in radiator. If bubbles, looks like head gasket or cracked head or cylinder.

Thanx

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