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Stemo

Coolant Loss Question

10 posts in this topic

I have a 2009 YZ450F with 38.3 hours on the current top end.  Runs like a raped ape and I really like the bike.  I recently have had an issue and I can't figure it out, so I'm coming here for some advice/help.

 

I'm losing coolant in the bike.  2 Trips ago to the track, I was checking my fluids prior to going and noticed I was low on coolant.  I was about 2 cups low - which I know is a lot.  I get to the track and notice a fluid leak in the bed of my truck.  I check the engine over and find I'm leaking coolant out of the coolant port right next to the exhaust.   Of note, the coolant looked "dirty" - not necessarily oily, but it looked darker than normal (blacker than normal).  I run engine ice in the bike so a darker blue as opposed to the normal color.  I take it apart and find a bad gasket.  I replace the gasket and the leak stops.  Topped off the coolant and go ride.  I put 1 hour of ride time on the bike.  I get home and notice I'm low again on coolant fluid.  I top it off.  I then run the bike up and down the street for 5 minutes (don't want to bother the neighbors too bad).  I check the coolant - no coolant loss.

 

Then yesterday I go to the track again.  Thinking I'm all good, but a little concerned I go for my warm up.  I ride and put 0.2 hours on the bike - a warm up and a few moderately hard laps.  I come in, let the bike a cool for 5-10 minutes and check the coolant.  I'm low again.  So I top it off once again.  Note that I did see blue coolant leaking from the bottom aftermarket skid plate (there is a sponge between the engine and the skid plate and I suspect I'm leaking from the weep hole and filling up the sponge which then shows a leak from the bottom of the bike).  I did not notice a leak from the weep hole.  Again, the coolant looks darker than what it was when I put it in.

 

I kind of suspect 2 things - bad seals in the water pump or a slightly blown head gasket.  So to test the head gasket theory, I make sure the coolant is filled to the top of the fins and start the bike.  I run it for 45 seconds and check to see if there is pressure building in the radiator.  No pressure build up that I can tell - cap came off easily without any sucking force.  I then start the bike with the radiator cap off.  Water seems to be circulating like normal - no bubbles.  When I hit the throttle, the water levels does rise in the radiator like one would expect as it gets more flow with higher RPMs.  But water doesn't shoot out of the radiator - it doesn't even overflow out of the radiator when I hit the throttle about 1/3-1/2 open on the blip.  So I'm kind of leaning toward it not being a blown head gasket.  Does this sound about right?  My question is what would be causing the coolant to get dirty/blacker?

 

So now I have water in the radiator because I don't want to keep wasting Engine ice at the tune of $24 a bottle to find the loss.  I've flushed the radiator now a few times and the water is clear with little black spots on it - can't tell if it is small rubber chunks or what.  I changed the oil and there is no coolant getting into the oil.

 

I'm kind of leaning toward a leaking weep hole of coolant when the bike is running really hard.  Would it leak coolant more when hot versus cold (I would think it would leak more cold, but I may be wrong).  This would mean the seals in the water pump may be bad or I need to replace the shaft, bearings, seals, etc.

 

Am I on the right track?  Thoughts on the tiny black chunks in the coolant fluid?

 

Thanks in advance for the advice/help.

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Dust the suspect areas with baby/foot/talcum powder.  The leaks will leave a trail.

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I dusted the area around the bottom of the water pump cover and there's water leaking like a sieve out the weephole.  Looks like a I need replace some seals, a bearing and possibly the shaft.  Thanks for the advice.  Anything else I should check?

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Ok, so I took the bike into the shop and replaced the shaft, bearing, and both seals.  It's no longer leaking from the weep hole.  I can't find any leaks now and neither could the shop. I took the bike out to the track last weekend and I'm still losing some coolant :banghead: .  In 1.2 hours of moderate run time, I lost 1.5 cups of coolant.  This seems still too much coolant being lost.  Granted, it is hot here in AZ in the summer with high humidity (monsoon season), so it is a worst case condition in riding for hot riding stress - but  I was riding fairly fast and not in tight single track going slowly.

 

So I'm now thinking I have either a bad radiator cap or blown head gasket - correct?  So based on reading some other posts on this, here is what I did.  I warmed up the bike then released any slight pressure on the radiator cap.  I then ran the bike down my street going through the gears 1-2-3, stopped and killed the engine quickly.  I slowly loosened the radiator cap to see if there was pressure built up.  Coolant puked out of the radiator as I loosened the cap.  I'm assuming this means I have a blown head gasket - correct?  I have changed my oil recently and there is no coolant getting into the oil - it's not milky and looks very normal for an oil change.  I check the coolant with the cap off and the bike running and there are some bubbles, but nothing extreme - I'm of the belief that just running the water pump with the coolant will cause some amount of bubbles regardless if there is exhaust going into the coolant (the water pump is a lot like a blender and I can't see how it wouldn't make a little bubbling in the coolant).  There is no oil or contaminants in the coolant that I can see.

 

Should I even try replacing the radiator cap?  It's cheap to do.  Or should I take the bike into the shop and have them do a leak down or test to see if the head gasket is blown (albeit not bad). 

 

Other than losing a little coolant - the bike runs perfectly.

 

Thoughts?  I can't believe I would have a blown head gasket and a bad water pump seal at the same time...The current head gasket has 38 hours on it.

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A leak down would give a more definitive answer, but it looks a bit like the head gasket to me.  The shop should be able to test your cap, too, BTW.

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A leak down would give a more definitive answer, but it looks a bit like the head gasket to me.  The shop should be able to test your cap, too, BTW.

Sorry to be a pain and I greatly appreciate your input. 

 

One more update from today.  I realized when I ran the other test and it puked out coolant, I had completely topped off the coolant to the rim in the radiator with no room for expansion when the fluid heats up.  After it puked it out, the coolant was down about~ 3/4" below the rim but still above the fins in the radiator.  So I reran the same procedure just now.  Warm up for 45 seconds, shut off, and relieve pressure.  Reinstall the cap,  then start it up and run down the street 1-2-3 gears "gettin on it", kill the engine and stop quickly.  Remove the cap (carefully).  This time, no pressure, no puking, nothing - seems completely normal.  I also dusted with baby powder and can't find any leaks. I'm going to get a new cap and try that this weekend while keeping a very close eye on the coolant and run it for very short time periods (5-10 minute intervals and not too hard).  If it's still having issues I'll drop it off at the local shop on Saturday afternoon (the shop is closed today and leave tomorrow for work until late Thursday night).  If I take it to the shop on Friday, they won't get it done before Saturday.  I'll try the radiator cap and if that doesn't get it done, I'll drop it off and do a leak down.

 

Thanks again.

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Yes, you do have to allow for expansion.  The normal height of the coolant after the radiator has been completely filled and has then been run long enough to reach the high end of normal temperatures is just above the tops of the tubes.

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Yes, you do have to allow for expansion.  The normal height of the coolant after the radiator has been completely filled and has then been run long enough to reach the high end of normal temperatures is just above the tops of the tubes.

Thanks Grey, you are a fantastic resource.  One final comment / bit of information.  When I got the bike home on Saturday after riding and cleaning it up, I went to check the coolant level.  When I removed the radiator cap there was a noticeable vacuum suction on the radiator cap.  I know when the coolant heats up it expands and when it cools down, it contracts - and the vacuum was from the lost coolant contracting.  I definitely lost about 25-30% of the coolant while riding it on Saturday - riding it pretty hard, it hot conditions.  Is this any further indication of a bad radiator cap or head gasket leak?  To me, if it was under a vacuum, then I would think coolant would be getting sucked into the cylinder then eventually into the oil (thus making it milky).  But maybe I'm off with my thinking.

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If there was a vacuum formed after cooling down, at least one function of the radiator cap is failing; the low pressure relief.  Looking at the bottom of the typical cap,  there is a small, spring loaded metal plate.  The spring under it holds it up against the rubber seal so it won't allow pressure out, but it should lift easily in response to outside air pressure being greater than the pressure in the radiator.   Either it's gone wonky, or something is restricting your overflow tube to the point that it's collapsing as things cool down.

 

radcap1.jpg

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