'03 yz450 seems to be running hot, smells like coolant.

This is a new to me bike. I've got 4 days of track use in on it. I didn't notice it smelling like coolant until yesterday. While riding at the local MX track, as soon as I would stop for a couple of runs I could smell coolant. I should've been getting plenty of airflow, I was moving fast the whole time.

I also noticed that yesterday before I loaded up the bike to head to the track that there was a coolant drip on the garage floor from the middle of the bike, it looks like there is a coolant overflow hose that dumps out right under the skid plate?

I pulled the cap off the radiator this morning and I don't see any coolant in there. I should be able to see coolant up above the tubes in the radiator, right? I've done some searching on here and I here some people talking about a weep hole, could someone post a picture of this is for me so I know where it is and where to watch for coolant leaking out?

I haven't changed the oil yet but I plan on doing that tonight so I'll see if I have a head gasket problem or not by seeing what the oil looks like. Assuming my oil looks good my first plan of action was going to be just topping off the radiator and seeing if it happens again, watching more carefully this time for where it's coming from. When I top it off, should I use something like Water Wetter?

A couple other things I know about the bike...

according to the guy I bought it from it had a full top end rebuild recently, within the past year and hasn't had much use since then (although he didn't have any receipts).

the bike has a 46 tooth rear sproket. could this be over loading the engine and making it run hotter than normal? I don't think it's this because I didn't seem to have any problems the first couple of days I took it out but I figure it's worth mentioning.

everything else seems good on the bike. It doesn't seem to be down on power compared to my buddies newer kx450 and I'm keeping up with or passing people at the track.

thanks ahead of time for any help,


My 450 runs pretty hot when you get things going, it's normal.

Your coolant missing is not though, under regular riding conditions you should not be losing coolant due to overheating. This means that your running the bike through the gears. If you were giving it all out in 1st and second not going very fast at all (insane hill climb, or mud hole) then you may have an issue.

Muddy tracks are a great example, where you can only get the bike going in 2nd/3rd if that, mud is clogging the rad and you need all the power of the engine to get going.

Regular track conditions should not be a problem.

The coolant expands enough that you should have coolant about 1/4" above the inner core of the rad when you look inside. This is just below the base of the filler neck, it should stay at this level and not drop any further. If you fill it up all the way, it will go back down to the level I specified after the bike gets to a good operating temp, this is normal. At this level the coolant has enough room to expand and not overflow to about 90 degrees celcius, at least from what I've tested.

The drip on your garage floor, did you have it ideling at any point on the stand or in that position before? The bikes will overheat if ideled too long.

Like I mentioned if you top the coolant right up there will be some leakage due to expansion when you get the engine to operating temp, which is completely normal.

Just use regular 50/50 coolant, works great. Do what you mentioned and fill the rad to the point specified and change the oil.

Start the bike and just take it for a quick 15 minute run, let the bike cool and check your coolant level and see what it's at. This should be where it stays, it should not drop any lower than this point. Riding the track for an hour let the bike completely cool off and check your coolant level again and see if it dropped or stayed the same.

That rear sprocket seems low, I don't know how the other years 450's compare with stock teeth but mine came with a 48 on the rear and a 13 in the front.

You might want to increase your rear a couple teeth to get that extra torque to keep up with your buddies on the track.

The drip on your garage floor, did you have it ideling at any point on the stand or in that position before? The bikes will overheat if ideled too long.

No, I rolled it out of the back of my truck and onto the stand, it hadn't been running for over 24 hours before I rolled it into the garage.

If that's the case then it sounds like there is either a leak on one of the hoses, clamps OR the weep seals on the case or water pump.

Find out where it's coming from.

When the coolant is under pressure it will come out quite a bit quicker out of one of these holes, you should start the bike up, get it hot and investigate.

Hopefully it's just a cracked or knicked hose or water pump seal, which is easy enough to replace.

Sounds good. Any chance you could snap a pic of where this weep hole is so I know where to look for leaks?

Right underneath the water pump, very small hole about 1/16 of an inch in diameter.

Usually there is one on the engine case somewhere but I'm having trouble finding it. Maybe someone else will chime in here with more info.

Follow your radiator hose down to the water pump. The weep hole is on the bottom. I've got an '03 YZ 450 also and mine started leaking back this past spring. Went ahead and changed both of the seals and gaskets for the water pump. Look at the pump shaft good to make sure it's not roughed up. No problems since the repair. Your manual breaks it down to make it easy.

Also check your header pipe, and make sure its not touching the water pump case, I had a worn out exhaust washer causing the pipe to touch the water pump, which led to over heating.:smirk::banghead::p all that troubleshooting for an easy fix.

Damn, I was hoping it's something simple. It's the head gasket. I got home and topped it off with coolant and it took about half a gallon. I cleaned everything off and let it run and I could watch it leak out at the front of the engine where the head meets the crank case.

I changed the oil and that looked good. I'm taking it into the shop tomorrow to see what they say. Hopefully I didn't do any damage while riding it with the leak.

One odd thing, after I changed the oil, I let the bike idle for 3 mins like the manual says. Then when I went to check the oil at the dipstick it started pouring out. I didn't change the filter and I put in exactly 1000cc into the crank case. Is this normal or could it be that one of the oil passages is blocked by the bad HG?

edit: I didn't drain the one on the frame because a guy at work told me not to bother with it. Could this be the issue, I didn't get all of the oil out?

Edited by dfinn

Could be positive pressure from the cooling system leaking into the oil system pushing the oil out?

Just a thought, I may be wrong.

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