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angrybob

06 YZ450 Consuming Coolant

12 posts in this topic

I have been adding just under a pint of coolant after every ride lately and the morning weather here is a nice cool 60F so there is no real reason to be overheating. Even though I ride single track the most, we pretty much stay moving.

The bike overheated once. I discovered that the waterpump seal went south and coolant was coming out of the weep hole for a couple of hours. Needless to say, I replaced the seals and shaft and added the Boyesen cover and impeller. I ride throughout the AZ blazing summer and every little bit of cooling improvement helps I guess.

Anyway, my guess is that the head gasket is bad from overheating as this is when I (started paying attention to coolant levels much more closely) noticed the problem. I see no signs of coolant going out the overflow and the oil is clean. Cap seems fine and probably not the base gasket.

Question: Is checking the head torque a waste of time or a good first step?

Question: Is the 450 head prone to warping?

I have 45 hours on the hour meter since I bought the bike used in March of 08. I checked the manual and it stated that I should inspect the piston every 1000km. Using our ride averages, this puts me at about 50 hours or so of engine time, plus the unknown love (or likely lack of love) that the previous two owners gave it.

Question: Is a compression check (or any other check) valid or is it a maintenance item that simply gets replaced after 'X' amount of usage.

Question: Parts needed: piston ass'y/rings/wrist pin/bearing, head gasket, base gasket...anything else to order in advance?

Anything else I should look at while I'm in there?

Ideally, a head bolt is loose and my compression is fine. I'm of the school that if it's not broken that it shouldn't be messed with. I have no idea though if that's appropriate for this machine.

Any help would be appreciated.

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I had this problem, less the overheat. It started with unexplained coolant loss. That first turned out to be the water pump, so I replaced the shaft and both seals.

I overlooked the water pump leak for a time because it wasn't very big. There was a buildup of oily looking grime around the oil tank balance hose under the pump when the bike got dirty, but this I originally took to be oil residue from servicing the oil filter that my son hadn't cleaned up well (it was his bike). It finally became more obvious. Lesson learned: smell the residue. The nose knows.

Anyway, it started using coolant again, and my first thought was the same as yours; head gasket. After all, I just did the water pump. But right after I did the rings and head gasket, I smelled coolant again, and the level was low after a ride. Now, there are a limited number of places coolant can escape from externally on a YZF, and even fewer that won't leak unless the bike is running. Running a finger over the escape hole confirmed it was leaking.

On tear down, I found the new shaft had already developed a significant wear groove in less than 20 hours. It wasn't huge, but a fingernail would snag on it, and it was only on one side. Disappointingly soft, IMO.

Nevertheless, I wanted to find a reason for it wearing on one side only. I ended up replacing the bearing, which honestly did not seem that loose, and both seals again. I made a point to prelube the coolant seal with a bit of moly grease, and switched from the premixed green stuff my son was using back to Engine Ice on the theory that the coolant's lubricity had something to do with it. So far, the leak has stopped.

BTW, I did not replace the shaft. I figured if it was that soft, I could polish it, so I chucked the drive end in a half inch drill and spun it in a piece of wet 320 grit until I was happy with it.

Checking the head bolt torque after the engine's been together so long won't tell you much, and the head is not really prone to warpage, but you should check the flatness. You can't do a meaningful compression test with auto decompression, but you can have a leak down test done to check the seal in the top end.

There's no wrist pin bearing, but don't forget new circlips and a gasket for the chain tensioner if you do the top end. Add a cam chain, because they're cheap.

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Thanks a lot for the detailed response.

I did not replace the bearing as it seemed fine. I will have some time in the upcoming week to check the water pump shaft seals. From memory, I have the same residue under the pump...I'll check that too.

I'm using standard Peak brand green coolant (~30%) and Water Wetter water (~70%).

I'm going for an easy ride tomorrow morning and I'll keep an eye on the weep hole area for coolant.

What is a reasonable time interval for rings replacement? Is it based on hours (just do it) or leak check results (check it until...)? I noticed above that you did not replace (or mention at least) the piston. Is it necessary to replace the piston for normal maintenance or just rings? It's my first thumper that I ride a lot. Two-stroke maintenance and top ends are simple, but I'm not sure what is necessary on four-strokes for parts replacement.

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What is a reasonable time interval for rings replacement? Is it based on hours (just do it) or leak check results (check it until...)? I noticed above that you did not replace (or mention at least) the piston. Is it necessary to replace the piston for normal maintenance or just rings?

You can approach it either way. You could re-ring whenever it leaks more than a certain percentage, and you'll get a lot of discussion about what that should be, but for practical purposes, 5-8% is a target range to stay below. Serious big-power racing engines rebuild at much lower figures.

You can just go by time, and set whatever interval you want, whether it be one year, two years... Depends on your use of the bike. I had 4 years and roughly 400 hours on my '03 when I sold it, and never did any of that to it.

As far as the piston goes, mine was in such good condition that I left it in, but replacing as a maintenance item is not a bad idea. Make your decision based on its condition.

In my case, I would not have gone into the engine had I not suspected the head gasket, and wouldn't have replaced the rings until sometime later.

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You can just go by time, and set whatever interval you want, whether it be one year, two years... Depends on your use of the bike. I had 4 years and roughly 400 hours on my '03 when I sold it, and never did any of that to it.

...

In my case, I would not have gone into the engine had I not suspected the head gasket, and wouldn't have replaced the rings until sometime later.

Wow. Its rare these days that I get the answer I wanted to hear :banana:. I typically don't take things apart that are perfectly functional.

grayracer513 - thank you very much. I'll have some time this week to have a look at the water pump parts this week. I'm now curious to see if there is wear on the shaft since I have about 10 hours since the seals were replaced.

This is why I love this forum!

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Rode 30+ miles to day of mixed terrain, but the weather was mild and not a lot of stop and go. I added water from my Camelbak 3 times during the ride at breaks. Twice was probably 6-8 oz. and the third was just a splash.

The coolant is not coming out of the weep hole. Its coming out of the overflow tube while I riding and when I come to a stop. I've never bee able to actually see it drip out of the overflow tube before this ride. There was coolant leaking from the skid plate with a wet trail up to the overflow hose.

My next step is to replace the cap. Why? Its easy, cheap, and 'could' save a lot of headaches. I'm curious though - the manual says that the cap opening psi is 15.6.

Question: Is there a reason to go with a different than stock pressure radiator cap?

I think this means that I don't have to check the shaft/seals since no coolant is coming out of the weep hole.

If so, the next step is head gasket. Thinking about it a little bit, I was only considering coolant leaking into the cylinder and going out the exhaust. But why not the other way? If there is a small leak, couldn't the coolant system get pressurized from the cylinder and push fluid out the overflow tube?

I've had no power degradation whatsoever. The bike runs awesome so I would think that anything that would create an obvious performance problem can be ruled out...at least for now.

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The coolant is not coming out of the weep hole. Its coming out of the overflow tube while I riding and when I come to a stop. ...

My next step is to replace the cap. Why? Its easy, cheap, and 'could' save a lot of headaches. I'm curious though - the manual says that the cap opening psi is 15.6.

Question: Is there a reason to go with a different than stock pressure radiator cap?....

..., the next step is head gasket. Thinking about it a little bit, I was only considering coolant leaking into the cylinder and going out the exhaust. But why not the other way? If there is a small leak, couldn't the coolant system get pressurized from the cylinder and push fluid out the overflow tube?

Have the cap tested at a dealer. All they need is the cap.

As far as the head gasket goes, yes, it's possible, and even more normal for combustion gas to leak into the cooling system than the other way around. There are tests for that, too, but they are trickier to perform. One is simply to take the cooling system pressure tester that the tech used on the cap, and screw it onto the radiator. Start and run the engine, crack the throttle hard a couple of times, and see if that causes the pressure to rise in response.

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Borrowed a radiator pressure checking kit from a buddy tonight. Cap failed the test spec'd in the manual, but the tool seems imprecise. Its a snap-on kit, but the whole manual process for checking is a little difficult to make a judgement if its close.

The manual states that it needs to hold the max pressure for 10 seconds. Using English units, the spec is 15.6 lbs - it could reach 14.5 lbs and would hold that pressure for very little time. After 10 seconds the pressure was 12 lbs.

Went to my local Checker Auto with tester in hand to compare. They stocked a 16 lb cap. It would hold about 15 lbs, but the leak was much slower. For $8, its worth a shot. I'm hoping for a ride this weekend and I'll check the system performance with the new cap. I can't imagine that the extra 0.4 lbs will exceed some critical pressure.

A little too late to do the pressure check on the system by cracking the throttle with the engine running. Will do that tomorrow...

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What is the drawback to going with a higher rated radiator cap?

I was also curious as to the 'normal' level of the coolant during/after a ride. If I top off, I am guessing that it will be lower to some degree without worry. My YZ250 seemed happy with coolant right at the top of the cooling element (bottom of the visible area in the radiator). Same for the 450's?

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You are correct as to the normal coolant level. Just above the tubes/core is where it should end up at the end of the day.

The higher pressure is its own hazard. Higher pressure increases the possibility of bursting a hose or radiator seam, or blowing a hose off. Apart from the danger that presents to the engine, 260+ degree coolant is nothing you want to be exposed to directly. However, if things are in good condition, a 1.5 bar cap should be OK to use.

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Well...I think I may have been chasing a problem that did not exist. My coolant level after riding only take a couple of ounces of coolant to be visible above the radiator tubes. Two rides in a row this has been the case.

I did have to replace the water pump seals as coolant was coming out of the weep hole and causing an overheat. After my overheating episode, I was paranoid about the coolant and topped it off before every ride :worthy: completely forgetting he fact that my 426 was happy at the radiator tube level.

Bottom line is that the head gasket does not need to be replaced.:lol: I threw a Boyesen impeller and cover at it and time will tell whether or not this was worthwhile - summer riding in the AZ desert. The bike is running great and the engine does not have to come apart.

grayracer513 - on one hand, my big thanks for your time spent with this as you did help me a lot with the step by step trouble shooting. That's what makes this a great forum! On the other hand, my apologies for chasing a problem that didn't exist at the end. Hopefully others will find this thread by the search and learn from it. I certainly did.

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