06 Yz 250f Lossing Coolant

I just put a new piston in and the bike runs great, the only problem is every time I go out for a moto I have to top my coolant off. It doesn't loose that much in between moto's but it is enough to where you cant see any coolant. The bike does not seem like it is running hot and the bike will run a 10+ lap moto perfectly. Any ideas?

Blown head gasket. I know you dont want to hear that but I am willing to bet money on it. It happens when you dont get quite all of the gasket material off from the old head gasket. What is happening is when you are on the gas the cylinder pressure is leaking into the cooling system and the pressure over comes the radiator cap and blows coolant out the overflow tube. To check for this route your overflow tube to the outside of the frame on the left side. Do a couple of starts with someone watching from the left side of the bike. Accelerate hard and they will see a steady stream of coolant come shooting out of the tube. If that is what you find then you will know 100% that it is a blown head gasket. Not a big deal. I have rebuilt a lot of engines and have had this happen once or twice. When you remove the head to replace the gasket make sure you check the head and make sure its not warped. If you dont know how to do that take it to a friend or shop that does. :p

Could also be the lower end of the front Radiator hose. I had a pin hole there. But I noticed the leak. Head Gaskets suck

How much coolant is being lost? I have noticed if i try to keep the radiator full it always blows out coolant to the top of the core (as looking in through the cap). So i stopped refilling now coolant never changes always at top of core. wont say it is common i have noticed the same on other bikes with no issues on any of them.

other way to see if its coming out of the overflow is to stick the tube into a small plastic bottle, just make a hole in the lid and poke the overflow pipe in. cable tie the bottle to the frame so as not to fall off. any coolant leaking will be collected in the bottle..

haha check this out.

Get my motor completely rebuilt. (Yes the WilliamsMotoWerx Mod bike) 1st rider after break in ride. I blow head gasket.

totally not cool. I will not goto cosmetic again. Im back to OEM. It wasn't a blown through it was like a crack around the cyclinder. Garbage.

I feel your pain! ripping the motor apart gets old, especially when you think it's time to be riding! :p

it could also be coming out of the little hole under the water pump, if it is that means the seals on the impeller shaft are gone

will the head gasket always blow soon after rebuilds? or will it take some time? I bought my 2006 yz450f in 07... and havent redone the motor since.. and today it started shooting a bunch of steam out of the overflow hose... does that sound like a head gasket?

I just put a new piston in and the bike runs great, the only problem is every time I go out for a moto I have to top my coolant off. It doesn't loose that much in between moto's but it is enough to where you cant see any coolant. The bike does not seem like it is running hot and the bike will run a 10+ lap moto perfectly. Any ideas?

If you just changed the piston... did you torque down the head bolts to spec? If not then the head gasket is your problem. The first gasket I put in, I did not tighten the inner head bolts enough and had exactly the same problem as you. I put another gasket in and the bike is fine now.

will the head gasket always blow soon after rebuilds? or will it take some time? I bought my 2006 yz450f in 07... and havent redone the motor since.. and today it started shooting a bunch of steam out of the overflow hose... does that sound like a head gasket?

Nope, you just overheated the bike. What were you doing just before you noticed that happening?

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