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Old 12-11-2010, 02:41 PM
Smokinjoe35's Avatar
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Default 06 YZ 450 losing radiator fluid after 1 ride


I have a 2006 yz 450 that runs and rides great. My bikes camshaft siezed back in May and I rebuilt the engine. I did have some shards of metal in my oil filter but there wasnt any broken pieces inside the engine.

Im now figuring my radiator had something to do with the sieze. Ill fill the radiator fluid full at the beginning of my ride and then upon return, about 3 hrs later, the fluid will be low enough that i cant see any under the cap. My left radiator has a nice dent in the lower pan and is pretty bent and was like this when i bought it. The radiator itself is bent about one inch out of place in a twist bend. I ride on power lines and trails and occaisionally up hills. For the most part my bike wont blow out any steam but the bike will blow steam out of the radiator overflow tube after about 10 climbs. My bike also gets very hot very fast when first started.

Could it be running out of fluid from overheating due to a non functional radiator? or is there possibly a small chip or crack somewhere inside the engine where the fluids leaking into and getting burnt up?
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Old 12-11-2010, 05:02 PM
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There should be a weep hole on the right side of the bike, when a bike starts to over heat or the pressure in the system gets too much it will weep out that hole. It will also weep out that hole when the water pump has issues.

are you getting milky oil in the transmission? if not there is not a leak into the transmission.

Have you done a pressure test on the cooling system?

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Old 12-12-2010, 01:38 AM
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My brother-in-laws 2006 yz450f was doing the exact same thing. We looked for any visible leaks and found nothing. I was pretty sure his head gasket was leaking. I was right.

We discovered that the reason his fluid would disappear was due to having a high spot on the cylinder which allowed the engine to leak compressed fuel/air into his cooling system. That leak pressurize the cooling system which then caused the fluid to leak past the radiator cap.

He took the cylinder and head to a machine shop and had them smooth it out (the cylinder was the problem, not the head), put it all back together with new gaskets and he's now good to go. Not sure if the 2006 just had a bad batch of cylinders or what, but that was why he was losing fluid.

One way to tell is to fill up your radiator, then start the bike with the rad cap off. Watch for air bubbles flowing through the system (his was pretty visible, and I knew it was the problem, but it took him a while to come to that same conclusion).

I'm not talking about a bubble here and a bubble there, I'm talking about a lot of bubbles flowing with the anti-freeze as it circulates through the system. His was very noticeable. You should be able to see them, but you will need a flashlight to make sure (since the light just doesn't quite penetrate past the neck of the radiator opening).

Of course you could be just leaking due to needing a new water pump, so check that first (you will see fluid at the weep hole if that is the problem). I would however, based off you already having a cooling problem, lean toward the cylinder not being as flat as it's supposed to be.

Hope that helps.
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Old 12-12-2010, 05:29 PM
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I sincerely doubt that the radiator, if it is dinged enough to stop some flow would cause a seizure. Unless you really boiled the bike you would not approach enough temperature increase to seize a cam in its journal.

A seized camshaft usually would be from over torque on the cam cap on one or both sides, generally one side, so the journal is galling the camshaft as it rotates. The 400/426/450 YZ's are somewhat prone to a small amount of overheating if the sit or are ridden slowly for extended periods. My 02 426 has steamed only once. At the GMB I +40 race, second moto we had a long period at the gate before the start and she puked some coolant at the pad/gate. I installed a Boyesen impeller and cover when we got home and have since had no problems in MX racing. I don't attempt trails and NW Florida/SE Alabama is flat.

I'd believe what Woody said about the 06 450F since there were several posts about them for a while on Thumper Talk when they were new and pretty plentiful. Check the head by decking it on a good straight edge and the cylinder with a straight edge you can move around easily, if you do not remove it, look at the piston top for scorched areas. When the head doesn't seat properly to the top of the cylinder or the head gasket is not properly seated the water and coolant will leave tell tale scorch marks where it sprays into the cylinder as the piston comes to TDC.

You may want to also use a non Ethylene or Polypropylene coolant and try Water Wetter or one of the other super coolants. As long as you don't race any AMA Pro events they are legal Best of luck on finding what the cause was and on curing the overheating problem.

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