My girlfriends 2002 Ninja 250 is overheating, and I was wondering where I should start troubleshooting?  It's water cooled, so I don't know a whole lot about it.  It sat for a while (3-4 months).  After it runs for a while, the reservoir overflows, and when she shuts the bike off, you can hear it boiling over.  What do y'all think?

I think you'd have better luck at www.ninja250.net

Does the fan (radiator) ever come on once it warms up?

I'd ask on that site Jeff provided too.

Thats what its supposed to do, unless by overflowing and boiling over you mean it is overflowing the plastic reservoir. Then I would say you had a problem.

The boiling noise is normal and the resivior/overflow/expansion tank is for when the coolant heats up it expands and the overflow goes into the resevior/overflow/expansion tank. I would check to make sure the radiator is full before you start it again.

I asked the woman, and she doesn't remember the fan coming on at all recently.  I'll definitely check to make sure the radiator is full before I do anything else.  It is overflowing via the plastic overflow container, and all over her left exhaust pipe.  If I don't find anything obvious, does anyone know how to test a thermostat?  Maybe that's not it.  She has a temp guage, and it runs into the red.  Is that controlled by the thermostat??  Anyway, thanks for your help.  I found a little information on the ninja site, but I feel out of my element there...  Intimidated by the 250.  How sad.

Just because its small doesn't mean its simple. The EX250 is as complicated as any full up sportbike, only in miniature.

Does it run hot while driving around or just while not moving or after you shut the engine off and it starts to boil?
Could be the thermostat.  If it were faulty and not openning completely that could cause the bike to run hot. Could also be the fan circuit is bad and not kicking the fan on.  The tests for these are fairly simple. But requires the manual (you have to take stuff apart to get at the parts in question) and some mechanical skill.

If you don't have those I'd recommend taking it to a shop.

We got back from a 20-mile ride yesterday, and it was overflowing as she was pulling into the garage.  Did the same thing when we arrived at our original destination.  We were sustaining 75+ mph speeds the whole way until we got into the parking lot(s).  I hope it's not the actual fan.  That little bastard is $270!  I'll hopefully be taking it apart sometime today.

I agree with JamesG that it might be the thermostat.

Hmmm... Might sound stupid but there is radiator fluid and water in there right?  because the radiator fluid will raise the boiling point of the water/mixture.

If it was the fan then it would only do it in slow/standstill traffic because when youre riding the fan doesn't do much good (ambient wind does a better job).

where are you riding at? if its somewhere southern then just take apart the thermostat and lock it/ break it whatever so it stays open to let the fluid into the radiator.  it will take longer to warm up but who cares (thats what jetting is for)  

My eli overheated but only in traffic. Now just a few mins of riding in traffic will sent it into overheat mode. The radiator has a sensor that turns the fan on when riding. Make sure that is working. Sart the bike up and as it heats up and the needle starts to rise close to red etc see if the fan comes on. If not the problem is in the fan temp switch. Locate it and pull the wire off the switch and hit it to ground. If the fan comes on there is the problem. On my eli it was up in the thermostat/radiator cap unit near the steering neck. On my Vulcan its on the radiator. replace it with a lower temp switch...On my eli a ZX11 was the right lower temp switch.
Cool.
Srinath.

I doubt its the fan.  EX250s aren't known for running hot.
What year is the bike?

First (cheapest) thing would be to flush and refill the cooling system and see if that helps. Then I would look at the thermostat being tired (you can do the old pot of boiling water trick to test it).  Or maybe the rad passages being clogged if hard water was put into it.

See, this is why I posted here instead of the Ninja 250 site.  Lots of great advice.  You all kick ass.  I'll let you know what the final outcome is.

Quote from: JamesGI doubt its the fan.  EX250s aren't known for running hot.
What year is the bike?

First (cheapest) thing would be to flush and refill the cooling system and see if that helps. Then I would look at the thermostat being tired (you can do the old pot of boiling water trick to test it).  Or maybe the rad passages being clogged if hard water was put into it.

Oh, yeah, if it's been sitting for a few months (in an humid area) and the fluid looks rust colored...bad...rusted or clogged with rust. Flow, check for flow; open the radiator cap and start the eng. You should be able to see the fluid moving/flowing, that also means your pump is good.

And as JeffD stated, remove the thermostat temporarily and see if that fixes the prob. If it does, it's the thermostat.

I just went through the same situation with my Ninja 250.
Turned out to be a LOT of air caught in the radiator.  You need to be very thorough when getting all of the air out - VERY THOROUGH!!!

Also, the fan comes on once the coolant is about 208 degrees, so once you DO flush the system and get all of the air out, you may either consider installing a manual fan switch or a lower set thermostat...

Good luck - and the Ninja 250 site, www.ninja250.net, has a LOT of information...  a LOT of information...


Rolly

Have you checked the oil level? It seems like low oil could cause the engine to run hot.

This is one of the reasons I bought the GS500. I didn't want to have to deal with a coolant system. There is something about the simplicity of an air cooled engine that I love.

before you go pulling the thermostat out do the simple thing and refill and bleed the coolant system. put fresh fluid in and make sure the properly and thuroughly bleed the system. i bet you a donut that that'll fix it.

Quote from: zoltanbefore you go pulling the thermostat out do the simple thing and refill and bleed the coolant system. put fresh fluid in and make sure the properly and thuroughly bleed the system. i bet you a donut that that'll fix it.

Yep, yep, agreed, I concur completely.

Okay, here's what I have done so far:

1) Drained the few drops of coolant that was left in the radiator
2) Flushed the radiator
3) Cleaned out the reservoir/overflow
4) Filled up the radiator with fresh 50/50 coolant
5) Filled the reservoir/overflow to below the LOW mark
6) Started the bike and let it run

Here's what I found:

- As the bike warmed up, the reservoir/overflow started to fill up with coolant (to be expected)
- The fan would turn on, only at high temperature (but the fan works)
- The reservoir continued to fill up until completely full, and spewed out all over the floor
- I turned off the bike to let it cool down (it never went into the "red")
- The coolant never went back into the radiator
- I smell like anti-freeze

My conclusion:

Something is wrong with the water pump, and the thermostat never got an accurate reading.  Poor circulation caused the overflow tank to fill up.  Why it never drained back into the radiator, I have no idea.

what this sounds like to me is a bad radiator cap. if you aren't familiar, the radiator cap regulates the pressure in the system. it has a spring in it and if the pressure exceeds a certian amount it bleeds off some coolent into the resevoir. the system needs to maintain pressure otherwise your coolent boils and you overheat. if the spring or seal has gone bad it could be constantly open to the resevoir which would account for the resevoir overflowing and the engine overheating. take your cap to your mechanic and have them pressure test it, should take 2 minutes.