Welcome to Netrider ... Connecting Riders!

Interested in talking motorbikes with a terrific community of riders?
Signup (it's quick and free) to join the discussions and access the full suite of tools and information that Netrider has to offer.

Honda CBR250 massive temperature issues arrrrrggghh

Discussion in 'Technical and Troubleshooting Torque' started by Climbatize, Apr 16, 2008.

  1. Hey guys had my 97 CBR250RR for a little while and been having some prety hardcore temp problems.

    The problem wasn't too bad it would hit the red every now and again and i had the bike serviced just recently. I got them to check the cooling system and it all checked out... apparently. Its got about 90,000 on the clock but the engine is performing great.

    So it started overheating again.. so much so it boiled the water and spat it out on the road at a set of lights... and i took it back to same shop a little pissed off. The sensor in the radiator was replaced as the fan wasn't coming on. I rode out of the bike shop and it started to overheat when i was near my house just 10mins later!

    The bike shop told me its likely to be three things, thermostat, blockage somewhere in the cooling system or the water pump impeller coroded.
    I'd pulled the rad off before the service and seemed OK, pulled the thermostat off last night and dropped it in boiling water and it opened after a second try and the impeller wheel in the water pump is def not coroded... and i hit the ignition and it seems to be turning fine. I ran it without a thermostat today because the weather was quite cool and the temp gauge was all over the place within 5 mins... from one end of the gauge to the other and overheating so much the needle on the gauge nearly snapped off. Fan still not coming on....

    Is it just me or is it bad design fault by honda that the sensor for the fan to come on is in the radiator and not in the block???

    Confused... help.

  2. Not sure what could be causing it.

    I don't think monitoring the radiator's temperature for the cooling fans is a bad design though. The thermostat determines whether or not the engine block needs cooling. The radiator's temperature sensor determines whether the radiator is cool enough to cool the coolant or if it needs some help from the fan. The thermostat's what's really in charge of regulating engine block temperatures.

    It makes good sense to me.

    If the fan isn't turning on, though, then that suggests a problem with the fan or radiator sensor, does it not?

    Possibly air in the system?
  3. But in their shop the fan was apparently coming on perfect relative to what the gauge was reading.. i think the fan comes on when the gauge reads just over half. Maybe the thermostat is a bit dodgey.. it took two tries for it to open in a cup of boiling tap water.. but it DID open.

    And please read, 'The sensor in the radiator was replaced'... that sensor is brand new honda item.. 90 bucks worth or something ridiculous.

    I should also note that when i purchased the bike, the thermo fan had been re-wired by the/a previous owner to constantly run.... for some reason. I didn't click to this when i bought the bike... so it was overheating LESS before the dudes at the bike shop fixed up the wiring.
  4. The bike shouldnt overheat in this sort of weather with a properly bleed system. Even with the thermo closed it shouldnt.

    checking the thermo u put in in cold water and slowly increase the heat, until u see it lift. record the temp and compare it to the owners manual.

    also are u judging the temp by what the guage says or is it actually really hot. Many guages are screwed. air bubbles around the thermo will throw it off like crazy.

    Make sure the water is flowing, open the rad cap(when cold) and run the engine.
  5. Yeah i'm going off the gauge... i had considered that, but on one occasion the temp has been hot enough to boil the water in the reservoir and spit it out those two rubber pipes that point down on these bikes. I was at the lights and smelt that distinctive smell of hot coolant coming through my helmet :shock:

    The fact that someone had hardwired the fan to be on constantly says to me that there was a cooling issue they couldn't be bothered with finding... just wondering if to fork out 85 bucks for a new thermostat..

    I had the kettle boiled and poured it on the thermo and it didn't open the first time.. i think these open at 80-84.. the kettle water would have been more than that surely.

    I havn't tried that method to see if the water is flowing yet.. but pulled the rad off again tonite and it looks clean as a whistle along with the hoses.
  6. Yeah, it would have been around 95-97 and the thermostat still took two goes to open. :wink:

    Put it in a sauspan of cold water. Put the pan on the stove and heat the water until it opens. Use a thermometer to determine the temp at which it opens. :)

    When you pulled of the radiator ect.. Did you flush the system and bleed the air out after refilling?
  7. That definitely is not the way to check a thermostat.
    Natta gave you the right method.

    How does the radiator cap look? Is the rubber (2 stages, the large part in the cap and the smaller section further in) in good condition without any sign of wrinkling?

    The cap must maintain pressure in the system to prevent boiling at the normal temp of 100C. Buy a cap before you buy a thermostat. The t/stat is only to help the bike warm up quickly, and maintain a hot temp when cruising fast in cold weather.

    If the temp is not maintaining without the thermostat you have another problem. You could have a very slight crack in the head or a minor leak in the head gasket which is allowing combustion pressure into the cooling system.

    Is the coolant in the overflow catch tank automatically being drawn back into the radiator when it cools down? If not, you are probably running out of coolant every day...and have a leak in the system. You must only check this (the level in the rad) when the coolant is cold, not even warm.

    What coolant are you using, just tap water? It should contain proper coolant (I use Mobil) and distilled or demineralised water only. If tap water has ben used the coolant will have a muddy appearance, or be brown instead of green. Poor coolant leads to internal corrosion which can seriously block coolant passages in the cylinder head, and radiator.

    Can you see clearly into the channels inside the radiator? Is there any sign of brown "mud" in there?

    All the best

    Trevor G
  8. Well even if it is the wrong method i'm sure that it has shown me it is slightly reluctant to open. Trevor G i think the tstat is also responsible for keeping the bike from overheating yeah..

    Not sure how i bleed the air out of the cooling system...?
    Any ideas on how to do that on my bike?

    Cap is fine and please read 'but pulled the rad off again tonite and it looks clean as a whistle along with the hoses.'

    If it was a crack in the head or HG i think i would notice a loss in power which there is none to speak of and doesn't appear to be leaking at all.

  9. Well, you're not exactly quite right. ;-)

    Firstly, do you know how a t/stat works? At what point does it start to open? How can you say a t/stat is reluctant to open unless you test it in the right manner? You must heat it up submerged in water, with a thermometer in the water so you can see at what point it opens.

    A faulty thermostat (one which is stuck and/or does not open properly) might help the bike to overheat if it restricts the water flow. A faulty thermostat is usually identified by not closing fully, or not opening evenly, as well as by using the test methods given earlier.

    A correctly functioning thermostat only helps the bike to warm up quickly and maintain a constant temp in cold conditions, by restricting the water flow until it reaches the preset temp..

    Once the water reaches the preset temp (82C or 84C or whatever is marked on it) the t/stat opens fully and can itself do nothing more to prevent the system overheating.

    But you are welcome to think whatever you like... :)

    There is no air to bleed out of a cooling system unless you have a leak somewhere. In that case, water/coolant will issue from that leak point once the system gets warm.

    Even if you fill an empty radiator, once you start the engine and the water warms up, any air "trapped" down low will quickly rise to the top of the water and disappear.

    If you can see bubbling in the water when the system is running (by looking in the top of the open radiator) you stand a chance that there is a head gasket leak or a cracked head. This will over-pressurise it and cause "boiling" water to exit from the overflow tank when the system gets hot enough.

    Because the water is mixing with air in this case, it cannot cool properly.

    You might not notice any loss of power on certain such faults. I am not trying to persuade you to pull the head off (although you might have to if it continues to overheat). Just watch the water flowing through the rad while the engine is cold, and check again as it warms up.

    Remember not to keep it idling too long as this will overheat it anyway.

    There are some minute crack events which only allow a leak at high temp.

    If the bike is overheating with the thermostat removed, and you are sure the gauge is accurate, and the pump appears fine without any sign of leaks, then there are not many other possibilites other than:

    1) muck in the water jacket/passages in the engine restricting flow of coolant

    2) blocked cores in the radiator restricting flow, or restriction of the air which is meant to cool the radiator

    3) faulty cap allowing water to escape at less than the marked pressure. This also lowers the temperature at which the coolant boils. I suggest you buy a new cap if you cannot have it tested at a radiator shop. Automotive ones might be able to do it, but they usually need the bike as well.

    Keep trying - all problems have a solution if you tackle them the right way.

    Trevor G

    PS Remember, you do not need the t/stat in the engine while you are looking for overheating issues. It does make the bike run better when it is working correctly, though. A cold engine won't run as nicely as a correctly temped one.
  10. Offtopic, for the sake of humour.

    Obviously you've never owned a Toyota MR2, Trevor - with the engine mid-mounted and the radiator at the front of the car; coolant lines running fore/aft under the cabin.

    It is said that the ancient Mayan civilisation developed the cooling system of the MR2, but the technology needed to easily service it without getting air trapped in the system has since been lost to the sands of time. :LOL:
  11. Mayans, christ... don't know if they would know how to cool a 3SGTE or even a 4AGZE
    But a CBR is not an MR2... i think it would make sense the air bubbles would rise & espcape if the cap was removed..

    I own an old toyota turbo car, besides the point, although, the rubber pipes from the radiator are caked with CRAP.
    Now recognising this means that there are other pipes caked with crap too. However, on the honda two of the rubber pipes are clean and the radiator has not a hint of sludge.. and any pipe i cant pull off.. considering i don't wanna pull the whole thing apart.. i'm guessing there is no blockage and pipes are clean... and started it last night with the cap off and it seemed to flow just fyne.

    I understand how a cooling system works.. mostly.. and a thermostat opens to prevent overheating. Well lets say if it doesn't open then could cause an engine to overheat.

    Anyhow i have ordered a new tstat and let you know how it goes.
    Cheers guys
  12. The Thermostat *closes* to prevent overcooling, and opens it once the engine is up to temperature.
    The thermostat on its own does nothing to stop overheating, Its actually there to promote the engine to get to operating temp faster, Once there it allows flow (Opens).

    The actual cooling is provided by the air going over the radiator, and the water flowing through the block. If no air is going over to cool it, it will overheat. If there is no flow, the water will have no place to dump heat and will keep rising in temperature.

    Sort of off topic, but I know in colder climates (Snow ect) That some people cover the radiator on the GPX to promote it heating up. The air flow is not needed with such a low ambient temp and the over cooling actually makes it run rough.
  13. But if the thermostat does not open how does the cool water from the radiator get to the block?

    If the tstat has seized then my understanding is that the cool water from the radiator cooled by airflow cannot flow to the block? is this not true?

    Obviously my point.
  14. Well i replaced the tstat with a brand new honda item and the god damn thing is still overheating! :oops:

    And it is dying on idle now :mad:
  15. i'll give you a tip.
    Trevor G is a mechanic.
    listen to his advice!

    for the record, i would put my money on the head gasket/crack in head.
    this is why a dodgy owner would hardwire the thermofan and then offload the bike ;)
    i would never buy a bike with a hardwired thermofan...
  16. Unfortunatly, Joel has hit the nail on the head, as usual.

    Chances are that you'll be replacing a head gasket very soon.
    I've just read this whole thread and recognise the symptoms that
    I've had, twice, in the 20 years I've owned my beloved FZR.

    For confirmation.
    Remove radiator cap, start engine, run at fast idle, if you see bubbles you
    need a head gasket.

    Check for milky sludge around oil filler cap, stick pinkie in there and feel
    around, sludge means new gasket required.

    For clarification, Sludge is caused by coolant getting into the oil.

    Bubbles are caused by combustion gasses getting into coolant.

    I hope it's something more simple but hard wiring the fan and selling is
    bad sign.
  17. As pissed as it will make me i appreciate the honesty...

    Although, if there was a crack in the head gasket i would imagine there would be oil floating in the radiator.. or water residue on the dipstick..
    I've had this problem with a car.. caramel dipstick.. bad sign.. but nothing of the sort with the bike.
    Appeared to be no bubbles when i checked the rad last night.. seemed to flow perfect.

    Forget about the dying at the lights info.. i suspect this is my own doing by removing part of the intake system.

    And i might add the the new tstat did help.. just a little.. doesn't overheat so quickly.. but obviously still a problem here and will hear any other suggestions.

  18. There might not be a gasket or cylinder head problem, but because you have seen one symptom of head gasket failure you seem to have become an expert...keep an open mind and don't limit the possibilities as to what is wrong.

    Is the bike adding water to the expansion tank when hot and drawing it back into the radiator when cold?

    Is the radiator full the next day after riding, before you start the engine?

    Just for your own sake you need to know that, if the bike was running without the thermostat at a particular temperature, adding a thermostat cannot make that bike/engine run any cooler than it was before. Adding a thermostat when none was fitted will only make an engine run warmer than it was without the t/stat.

    If your original thermostat was not opening completely (and I wonder if you compared the two before fitting the new one) then that would help it to not run as cool as it should. A thermostat always adds some restriction to the flow of water in a cooling system, even when it is fully open.

    Have the radiator cap pressure-checked as well. A radiator cap will usually fail as readily as a thermostat, but it allows water to escape before the design temperature (which reduces the cooling effect and increases the coolant temp) and then can prevent the coolant from being drawn back in when the system cools.

    It also allows the coolant to boil before it should (although coolant should never boil!) and boiling coolant loses almost all its cooling ability.

    Are all the fairing duct pieces in their correct place?

    Do you have any broken or removed fairing parts near the radiator?

    Are any of the fins on the radiator core bent or closed over?

    Are there bugs clogging the fins and the core on the outside of the radiator?

    Is the radiator core and fin area absolutely clean?

    All the best

    Trevor G

    PS A cracked head or damaged gasket does not always mean water in the oil or oil in the water.

    PPS Playing with the air intake, reducing the baffling or whatever will tend to make the bike run leaner which will tend to make the engine run hotter. You need to jet up if you want to do that. It is always better to solve one problem before creating another...
  19. On a recently rebuilt scooter which had been having seizing problems, changing the mid range jetting up a tad solved it all :)
    The extra petrol into the cylinder cools things down a lot (Not to mention the oil, was a 2t scooter. In the past I had seen it seize running 25-1 mix ontop of the oil the oiler was providing. Someone had stuffed the jetting up massively.)
  20. Yeah well owning a turbo EFI car with a computer capable of learning i figured a plastic insert with two circular mesh inserts could be done away with for more airflow.. anyhow i figure thats why the bike dies on a long idle. Besides the point.

    I don't claim to be an expert at all.

    Running the bike without a tstat make the temp gauge schizophrenic.. it would go from ice cold to boiling hot.. 14,000rpms+ made the gauge read cold... As soon as i let off the throttle it would shoot to the red.

    The exhaust blew a fair amount of steam yesterday when i started it.. but it was not consistent. The reservoir for the water seems totally unchanged for the last couple of days. Even after topping up the rad and losing water when i undid the tstat housing.

    Side fairings are removed and have been for the last two days. Radiator looks a little hard done by.. but not so much so to produce these kind of effects..

    Thermo fan is still not coming on.
    Which is more frustrating because the sensor was just replaced.