2007 yz 450f losing coolant

So im losing coolant, twice now topped of ive lost about 1/4 of the coolant. The oil both times wasnt grey or lighter at all really. My son said he saw smoke for a second but i had just went thru a puddle. Riding at the track yesterday i lost the same amount again and oil was fine. Do I check for bubbles while running with the rad cap off? Starting seems ok still not to bad. Runs fine no smoke what so ever. I am running water wetter with regular not distilled water. I meant to drain it i know itll corrode.

You could just be loosing it through overheating. You should be running 50/50 or a coolant mix that can stand heat not to mention corrosion protection.

You could have a minor leak in the head gasket that is sending exhaust or pressure if you like into the water jacket. Pressurizing the coolant system and pissing it past the radiator pressure cap.

Or the radiator cap could be defective or have s bad seal

Ok ill flush it. Is engine ice a good brand to use? Ive heard bubbling coolant means exhaust gases leaking thru the head gasket. I just hope thats not it. Maybe it is overheating and spewing it out.

There is a difference between bubbling coolant and the normal foamy nature of the stuff.  It's also normal, if you fill to the top, to push out coolant until the tops of the tubes in the radiator are just covered.


  • Have the cap tested for correct pressure
  • Check for leaks, including around the weep hole under the water pump (might need to dust up the area with foot or baby powder to spot the leak, and water pump seals may not leak under every condition)
  • There is a test that can be done for the presence of combustion gasses in the cooling system. 

So i flushed the radiators and put green 50/50 premixed coolant in amd riding today i lost alot of coolant again. Totally forget to check for bubbles. Autozone rents a kit to check for rad exhaust gases. Ill prob checkl that.. And my oil again. Idk how it not changing the oil color...??.. The cap seems fine but maybe a new one wpuld solve this. Who wants to put in head gaskets and the like..... It has a new top end less than 6 months ago

Just found the leak!!!!... Weep hole!!! Whats the fix? Just rhe two gaskets? Ones oil side ones punp side??? Thank gosh its not the head gasket man im so relieved thanks again for tt guys an help...couldnt do it with this help an knowledge...i was straight up thinking about going back to 2 stroke..

The fix is to remove the right side engine cover (drain the oil and the coolant) and replace the water pump shaft seals and bearing.  You may also find that the coolant seal has worn a detectable groove in the shaft, in which case you'll need to replace the impeller shaft as well.  


Read: http://www.thumpertalk.com/topic/841710-04-450-coolant-leak/


While you have it apart, you'll want to check that the balancer shaft, which both drives the impeller and supports the inboard end, is OK.  More than 2-4 thousandths of an inch up/down play (perpendicular to the shaft axis) is a sign of a worn bearing, which will cause the impeller shaft to run off center in the seals so much that they will leak.  



Ok, ill ride it again before i do the work probably. Can you actually feel that 2-4 thousandths? When i take the cover off what am i doing to determine the up and down play?

The best bet is to set up a dial gauge on the shaft, then attempt to move it vertically, up/down, and see the clearance the bearing has. 

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