Overheating

[stoinkythepig]

My '01 ZX9R suddenly overheated after a ride a couple of weeks ago while I was letting it idle to burn up the gas in the carbs (a habit I've developed whenever the bike is stored for more than a couple of weeks) before putting it away. The temp soared to 239 F rather quickly and the fan never kicked on. The overflow tank puked on my driveway, so I know the temperature sender is working.

Step 1. I drained the coolant, replaced the fan switch which worked intermittently in testing, completely cleaned the radiator (it had a lot of crud stuck in it on the outside after 89,000 miles) and filled with new coolant. Still overheated.

Step 2. Drained the coolant and removed and tested the thermostat, it passed the test. Put coolant back in, and of course it still overheats.

Step 3. I put pressure tester on the radiator and pressurized it to 20 PSI. It dropped 3 PSI in an hour and a half with no signs of external leaking. I pulled the spark plugs and cranked it over. I am 99% sure I saw mist come out of the #3 hole. I re-pressurized it and I'm giving it another hour and a half too see if it does it again.

I assume it has a leak in the #3 hole that's letting combustion gases into the coolant causing the overheating; and I figure it needs a head gasket or a new head, but just in case, I thought I'd ask if anyone else has other ideas.

NOTE: I'm due for a new head (or engine depending on the condition of the cylinders). Some of my valves are on the smallest shims available and it's cheaper to throw a used head ($150) on there than it is to buy 16 new valves (at least $200). The timing could not be much better either since it's still Winter. If the engine is shot, I'll have a bigger decision to make...

[CBR929RE]

did you get the fan to turn on?

[cdseven95]

You can test for hydrocarbons at the filler neck with a rented kit from an autoparts store to see if its pushing coolant..

I had a similar issue with the zx11 blowing coolant out of the overflow but that was fixed by bleeding at the w/p housing...

Can see the coolant circulating..?

[dontpanic]

Fuse for radiator fan?

[stoinkythepig]

The radiator does not get hot enough to start the fan, but the fan switch can be by-passed and the fan will run, so the fan and the fuse are fine.

The overheat condition happens really quickly. It'll go from stone cold to 230 F in about 8 minutes at idle. The problem is not in the radiator side of the equation. Coolant seems to be flowing quite well. If I rev it with the cap off, the flow is quite obvious.

[Degsy]

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Head gasket leak pressurizing the coolant system.

[stoinkythepig]

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Head gasket leak pressurizing the coolant system.

I can't think of anything else either.

[Danz19899]

did you check if the rad cap is holding pressure? fan should turn on any time over 220 on the temp gauge no?

[stoinkythepig]

did you check if the rad cap is holding pressure? fan should turn on any time over 220 on the temp gauge no?

The tester I'm using does not fit my cap. I suppose I should change it, just in case, but I don't think it's the problem.

It'll turn on when the coolant in the radiator hits 212. The coolant in my radiator is not getting very hot, just the engine gets hot.

[Danz19899]

that's really weird shouldn't the coolant be flowing? maybe water pump worn out?

[BluGixxer]

that's really weird shouldn't the coolant be flowing? maybe water pump worn out?

Sounds like a good thing to check, water pump and airpocket of some sort,. Air pocket in water pump equal cavatation, no coolant movement, radiator wouldn't get hot, but motor would overheat, when coolant did hit hot motor , expand quikly and spill out overflow,
Air pockets don't always work themselves out ,
Another thing to look out for , when running carbs/motor out of fuel , it leans out and runs hot , as for how long , that depends on setup , could be quick or could start as soon as you shut off the fuel.

[stoinkythepig]

Sounds like a good thing to check, water pump and airpocket of some sort,. Air pocket in water pump equal cavatation, no coolant movement, radiator wouldn't get hot, but motor would overheat, when coolant did hit hot motor , expand quikly and spill out overflow,
Air pockets don't always work themselves out ,
Another thing to look out for , when running carbs/motor out of fuel , it leans out and runs hot , as for how long , that depends on setup , could be quick or could start as soon as you shut off the fuel.

The bike has been run out of fuel, just prior to storage, this way for years. This is the first time it's done this. It overheats with the petcock on too, at idle and while being ridden. It's not a lean condition that's causing the overheat.

I have drained the coolant on this bike and re-filled it in the past without any issues. I use the method described in the factory service manual. I am not introducing air into the system and the pump is moving plenty of coolant

Coolant can flow very well and there can be no air pockets causing cavitation at the pump, but if combustion gases get into the coolant at the head, the bubbles prevent the coolant from adequately removing heat from the metal. In this situation, the engine will get very hot and the coolant won't. I am very sure this is what's happening, I was just looking for other thoughts and I very much appreciate all the responses.

One other thing I forgot to mention, There is a steady stream of little bubbles that come out of the coolant when the engine is running. They continue until the point where the engine is hot enough that I have to put the radiator cap on or risk spilling large amounts of coolant.

[stoinkythepig]

Thought I'd post an update...

I replaced the head gasket, and the head since the original valves were nearly out of lash adjustment. I gos a 28,000 mile used head for 150 bucks and it works fine.

The bike ran perfectly when I was done, and for the next 500 miles.

On Thursday afternoon, the bike ran really hot (200 to 220, normal is 155 to 190), all the way home. I was like WTF? and freaking out thinking the original problem was back. When it cooled off I drained the coolant and checked everything over. It all looked good, so I tested the thermostat and this time it failed. I decided right then that I'll never re-use a thermostat again.

A quick trip to Advance Auto Parts, $4.99, and a little time drilling and trimming the Stant 13006 to make it work in my application, followed by 20 minutes of re-assembly and coolant filling and it's back to normal. I could not wait for an OEM thermostat to be shipped as I'm planning to take the bike on a 1000 mile ride/business trip next week.

I have to say that while I like working on bikes, a 2011 ZX10R with ABS would be a cool use of my annual bonus...

[Cerberus]

out of curiosity, how were the coolant passages through the head/deck plane? I've seen them obstructed with chunky hard corrosion crap build up, and that kind if thing is a guaranteed hot spot causer..

that was going to be my suggestion, had this not been a subject that had already been resolved

[stoinkythepig]

out of curiosity, how were the coolant passages through the head/deck plane? I've seen them obstructed with chunky hard corrosion crap build up, and that kind if thing is a guaranteed hot spot causer..

that was going to be my suggestion, had this not been a subject that had already been resolved

The coolant passages in the engine and radiator were practically spotless, thankfully. Right now, the radiator fan kicks on at exactly 212 and immediately cools the engine in a rapid fashion, exactly as it did when the bike was brand new. The fan switch must have been getting worse and worse because the temperature at which it would turn on was going up and up over the years. I assumed it was due to buildup in the cooling system after 90,000 miles of use. I am glad I was wrong.

Here's what I think happened:

The bad radaitor fan switch caused the first overheat.

The first overheat weakened the head gasket causing it to fail.

Subsequent testing to overheat condition, to make sure it really was the head gasket and not something easy to fix, weakened the thermostat causing it to fail 500 miles later.

I'm really glad this all happened in March/April when the riding sucks and the temps are cool. I rode 52 miles on Thursday with a closed thermostat. The only cooling the bike got, the entire ride home, was through two, roughly 2mm thermostat bypass holes. Had it been 75 degrees outside, I'm sure I would have been sitting on the side of the road. waiting for the bike to cool multiple times.