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GPX250 Overheated

Discussion in 'Technical and Troubleshooting Torque' started by L0Ki, Mar 15, 2008.

  1. Today when i was riding home i noticed my temp gauge was in the RED like at the end of the scale. I had been sitting at lights for a couple of minutes about 2mins before but honestly couldnt tell you if it was hot just then or if it had been like that the whole time. By the time i had babbied it down the road to my house the temp had gone down abit but was stil in the red.

    So my question is what do you think it could be?

    I was thinking waterpump. I checked the overflow box and its about halfway full so theres water in the radiator. Not willing to take the radiator cap off just yet as its still pretty hot.

  2. Does the fan come on?
  3. How long have you been riding before you realised the temp?
  4. Dont know about the fan as i turned it off once i got home and have left it at that. Should the fan have been on once i switch the engine off but still had the key in the 'on' position?

    If thats the case then no the fan wasnt working. Which could have been my problem. But would a faulty fan make the bike run over the red on the temp gauge? It was over the red part of the temp gauage so obvisously somethings had gone wrong.

    I had probably been riding about 20mins but before that i had a 15 mins stop at someones house and before that i had been out for about and hour and abit. I dont recall the temp being hot during the first ride though, but i cant remember eve looking at the gauge.

    The bike didnt seem sluggish or anything, but boy was it hot when i got home. It had the smell of something that had just been welded. You know the smell I'm talking about?

  5. From memory the fan on our bikes only operates when the engine is running.

    Even then, the gpx cools off a shitload from just a little bit of air moving over the radiator - eg riding down hill.

    Check the oil?

    I'd be thinking it's the cooling system most likely though, perhaps a blockage in the lines?
    • Like Like x 1
  6. In traffic, yes.

    The fan will still go on after you turbo the bike off.. but not for long I think. When its in the red it should certainly be on.
  7. Yea oil is fine. Its at about half way.

    I'll probably flush the system next weekend.

    Whats the actual process for flushing the radiator. I've only ever just run distilled water through the radiator until it comes out clean. Is there a special product like draino or something for this?

    Ill check the fan out 2moro. But how do i actually check it. When should the fan come on? I dont wanna leave the bike sitting there idling until it cooks again.

    Thanks so far for the tips
  8. You checked with the bike level, vertical in both directions?

    NO! No product, just clean or distilled water, two lots. Undo the lowest point, often the water pump, and also the bottom of the radiator plus the overflow tank.

    Make sure before you undo anything that you check the level of coolant in the radiator - it is possibly low. Sometimes the overflow cracks and the radiator just draws in air, instead of coolant.

    The fan should be connected to a temperature sensor (or sender as it is sometimes called) on the radiator. If this is a single wire sender then removing the wire and touching the terminal on the end of the wire to the metal part of the sender should turn the fan on when the ignition is on or the motor is running.

    If it is a 2 wire sender, then joing the two wires together should start the fan. The sender might have failed. While the radiator is empty remove the sender and place it in boiling water - you need a multimeter to check that the terminal is connecting to the metal base (or "earthing" via the metal base) or that there is continuity between the two wires.

    A new sender probably won't cost the earth if you have any doubts.

    Also check that the fan is OK by using alligator clips (get 'em from a Díck Smith or similar) to connect one side to 12v and the other to earth. It should spin. You could have a dead fan.

    All the best

    Trevor G
  9. also check the thermastat in a container of hot boiling water to see if it opens ( remember that water under pressure boils at about 110 deg C )
  10. The fan on a GPX will even come on after the bike is turned off. I know because it scared hell out of me one day - two steps from the bike and it comes roaring to life...
  11. Yea i think that was my problem. I found that there was no coolant in the radiator today. I thought it was just because i couldnt see down it enought as its just a small length tube before it disappears into the radiator.

    I had to put about 500ml so half the water back into it.

    Im thinking (or hoping) its the overflow problem because otherwise im guessing its a blown head gasket.

    I started it again after i filled her up. I did it without the radiator cap on until bubbles stopped appearing. The fan was working fine. The temp never got above about 12-1pm if you just imagine the hour hand on the temp gauge.

    Thanks for the help so far.
  12. You topped it up with coolant right, not water?
  13. Yea coolant, 50/50 mix with distilled water. As stated in the manual.
  14. Did you do the coolant previously?

    If not, there is a real danger (according to mechanics I know) that two dissimilar coolants can react together. I think you will find a similar warning on the bottle.

    The coolant has dropped in the radiator because the overflow system is not working properly or you have a leak, either at a hose or via the water pump or similar, which depressurises the radiator and prevents it drawing coolant back from the overflow.

    Even a faulty radiator cap can be a problem - remember they have two seals inside them. Any perishing and it must be replaced.

    Check or replace the overflow hose, and make sure that you can syphon water/coolant back out of the overflow before hooking it back up to the radiator.


    Trevor G

    PS A blown head gasket will either pressurise the radiator system (frothing, bubbling or oil in coolant, or add water to the oil in the engine. Water in the oil shows up with a milky appearance. I would say the overflow/replenishment system is faulty.

    BTW A little known fact is that if there is unsufficient coolant then the temp senders don't work properly (won't come on) because they need liquid, rather than steam, to make the temperature contact.

    In that way the temp gauge (on the cylinder head) can still show a high reading, but the fan switch (on the radiator) won't be triggered to cool it, since there is no/not enough hot liquid in it. What is there (steam, maybe?) is being cooled down anyway.
  15. Yes i had flushed the systenm before with the same coolant so it shouldn't react.

    How do i test the overflow system? Do i just replace the hose. Is that all i can do?

    The cap looks ok. But could it let steam out from the sytem if it wasnt sealing properly? Causing the lose of water. Seems unlikely as there was a pretty large amount of water missing.

    Can you explain how to test it a little clearer as I'm not sure as how to syphon something with radiator fluid in it.

    How would you see bubbles. Obvisously you have to take the radiator cap off first and just run it from cold watching for any bubbles? Would that be correct?

    Oh are you just explaining as to why the fan moight not have been working when it overheated? Sound likely that would have been the case.

    Thanks alot.

    EDIT: I think i have a blown head gasket because it keeps going down without the overflow filling up or going down. But you;d think with a blown head gasket it would take whats left in the overflow until there was none left? So that still leaves the question of why that would be happening. Probbaly a cracked hose or soemthing like you mentioned?
  16. Just an update.

    The bike seems to be staying just under or just on the red zone of the gauge if its not moving such as at traffic lights.

    COuld this be the thermostat or soemthing wrong with switch that allows the fan to turn on. The fan comes on but only when the needle is nearing or on the red zone of the temp gauge.

    Im starting to think its not a head gasket anymore because of this. My reasoning for the lose of radiator fluid is that when its heats up so much the overflow overfills and fluid drips from the overflow hose. Could this really cause it to lose 500ml of fluid? (not sure how long it took to lose that amount)

    I also changed the radiator cap (2nd hand one) and nothing changed.

  17. Water must be leaking somewhere even with a blown head gasket - then it can end up in the engine oil. It doesn't just evaporate.

    Most likely is a leak you have not yet spotted, such as from the water pump or a poorly tightened hose/clamp.


  18. Here's how it works.

    The coolant heats up in the radiator and, once the pressure exceeds whatever is written on the cap (eg 14 = 14 psi, 1 = 1 bar = 15 psi and so on) the excess water is transferred to the expansion tank.

    When the radiator cools down, providing the cap has not been removed and there is no leak anywhere (and I mean anywhere) in the system, the pressure in the radiator/cooling system drops until it becomes negative and draws coolant back into the system from the overflow tank, via the radiator cap again.

    If the hose to the expansion tank has even the slightest leak no coolant will be drawn back in and the level in the system eventually drops through the continual heat/cool cycling every time you run the engine.

    It doesn't take long to lose coolant once you have a leak, maybe 3 months to lose 500 ml? It could take a lot less time if the leak is on the engine/radiator side of the system, rather than in the coolant return line.


    Trevor G
  19. Thanks for the info.

    But can anyone confirm that the GPX is meant to run that hot. It gets to the red line and just below it and stays around there while at lights. Is this for everyone that owns a GPX? Im kinda thinking its not, because it looses coolant at this level a little bit too much.


    Will go out today and check the hose clamps and all fittings for any loose ones. Im pretty sure the overflow tank is working because it was overflowing when i got back froma ride yesterday only for it to have gone down to just above low.
  20. On a really hot day, mine never reached the red part, but I didn't ride it hard at all, and the longest I was at lights was about a minute, the fan was on from almost the instant I turned the bike on.