'06 450F whistling and steaming

First and foremost my bike runs excellently. In fact, even when I'm noticing the issues I'm reporting here, I've never had a loss of power while riding and it starts on first kick no matter what.

A few things I find very odd that have been happening recently:

1) I have to refill my coolant after every 90 minutes or so of riding. On a standard two day trip, I might put in 6 or 8 ounces of coolant (I suspect, but not measuring) each time I come back to camp to get food/water. During the entire trip, it feels like I've gone through a fairly large amount of the 50/50 I'm putting in. I originally used Yamaha's coolant, but noticed the same issue. And even though I'm filling up when we come back, I've probably seen and heard the steam/boiling for a good 30 minutes prior. So I would have been riding on what seems like empty coolant for a good period of time.

2) I can hear the coolant or lack of coolant boiling/sizzling as I ride, if I happen to slow down enough to notice it.

3) If I kill my bike after riding it really hard, or sometimes even idling down hills and waiting on others, it starts to whistle from the bottom of the engine for almost an exact 2 to 3 seconds (when it occurs, but isn't every single time) and a white steam comes out. The steam smells, so I'm assuming it's burning coolant or something else possibly, or maybe just the engine letting it out as it tries to cool off.

4) Sometimes even as I ride I'll notice the steam coming from the front and sides of the engine.

5) I have not noticed any coolant or steam coming from the weep hole on the right side of the engine. In fact, I haven't noticed any buildup of anything near there.

6) The rider that spent most of the time behind me this trip said he noticed oil burning when I took off, but after that he said it was gone.

Now that all that is out of the way, a bit about my riding style (maybe somebody can point out something I'm doing to cause this) and the bike:

1) The engine is completely stock except for the Z-Start Pro clutch I put in at the beginning of this year. The clutch seems to run great. I haven't had any issues with it.

2) I'm entirely trail riding 100% of the time. Tight turns, wide open trails at points, lots of slowing down going down/up steep hills with ruts, steep hill climbs, your standard trail obstacles.

3) A lot of the time I'm behind a rider on a 125 and prefers to go slower, which seriously disappoints me, but I'd prefer to stay in a group and have fun than veer off course alone.

Here's what I know about my maintenance:

1) I change the oil after every weekend trip and it's usually a tan/milky color.

2) I clean the air filter after every trip and the intake seems free of debris.

3) I have not checking my timing. I realize I need to, but up until this year it maybe had 25 hours on it total. This year along I've probably doubled it so far. I would like to do the maintenance myself, and I could use a few pointers on what I need to check and what the intervals are and possibly some URLs with information on doing so.

Thanks in advance!

Actually, no, that would not explain the milky color of the oil. The water pump seals cannot leak coolant into the engine (that's why the weep hole is there). What I'm suggesting is that the leak is there and he just isn't seeing it happen.

If the oil is in fact contaminated with coolant, a head gasket is more likely the cause.

I appreciate the great responses from you guys. Hopefully in the next couple of weeks I'll find some time to examine said locations and get everything fixed up.

If I was you, I would beg, borrow, or steal a cooling system pressure tester to figure out exactly where you are leaking. The previous comment may be exactly correct, but if so, you seem to have more than one problem. You will be money ahead, even if you have to rent a pressure tester, because you will know exactly what you are up agains, and will likley avoid unneccesary repairs.

I have an 07 yz450 and I believe the 06 and 07 use the same water pump set up. The design has some flaws in how the impeller shaft is held and quite often they wobble slightly as they turn, which wears out the shaft seal extremely quickly and doesn't do the shaft any good either. Mine started leaking with ~20 hours on the bike so I replaced the water and oil seals, the shaft, and both bearings. I've since put 40 hours or so on the bike and the problem has not re surfaced however I monitor the fluid level quite closely.

Some tell tail signs of a head gasket would be lack of compression and a white cloudy look to your exhaust (this could be mistaken for burning oil like your friend thinks your bike is doing).

I have an 07 yz450 and I believe the 06 and 07 use the same water pump set up. The design has some flaws in how the impeller shaft is held and quite often they wobble slightly as they turn, which wears out the shaft seal extremely quickly and doesn't do the shaft any good either.
You are likely basing your assessment of the design on the mistaken belief that the shaft is supported by a single ball bearing, which, if true, would allow the shaft to wobble off axis, since it takes a minimum of two such bearings to ensure axial alignment. What you missed is the point that the balancer shaft supports the inboard end, and thus the balancer shaft bearing becomes the second bearing on the impeller shaft. There's nothing wrong with the design, as long as both bearings are intact, but that was the source of my problems in the link I posted earlier.

Ah yes this sounds like what I had read when mine went. Perhaps there was something amiss with the tolerances on one of these bearings?

Perhaps there was something amiss with the tolerances on one of these bearings?
You could say that. The right side balancer shaft bearing had a spalled outer race about half way round, and the shaft had .017" of axial clearance, causing the impeller shaft to run out excessively, and the pump to leak.

Tan milky colored oil, riding on trails, hmm, any water crossings? Have you rerouted your vent tube? Maybe picking up some unfriendly moisture that way? Just saying.

Tan milky colored oil, riding on trails, hmm, any water crossings? Have you rerouted your vent tube? Maybe picking up some unfriendly moisture that way? Just saying.

My thoughts exactly. BTW, next time your bike is steaming out coolant be sure to pull over and let the bike cool down.

You also might check your radiator cap, it might be weak and letting your coolant out while riding ( I have had that happen myself, I thought it was engine problem when it was that ).

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