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1991 250 GPX overheating!

Discussion in 'Technical and Troubleshooting Torque' started by phedus, Apr 10, 2011.

  1. Hi all,

    I did an oil and filter change yesterday, took it for a decent ride on the highway to check for any leaks etc. and everything was fine.

    I went for a ride with a few old mates today up Mt Mee here is QLD and she started to over heat.

    Now this si where she gets the most work out so I always watch the gauge, but this time it was the coolest day yet this year and i watched as the temp slowly kept rising so I pulled over to find that the overflow was bubbling! and WHITE smoke was coming out off the oil overflow (i think its the oil overflow).

    I figured this was because I may have out a little too much oil in after forgetting to account for the new filter but this problem quickly solved itself after spewing the excess oil out - sitting at a perfect level now.

    After playing with it for a while I noticed the radiator fan wasn't turning on at all.

    Fuses are all OK and wires seem to be fine.

    Has anyone had this problem before?

    Could it be the thermostat and if so how do I test it?
  2. Thanks for the help jd, turns out my radiator fan thermo switch inst talking to the fan. I'm hoping this is the only problem.

    Not sure the water pump is working too well either as the coolant was red, and my emergency fill up was green but when i tool the switch out - only the red dripped out so I may have a bit more of a task on my hand.

    As always suggestions and advice welcomed
  3. Do you think the fan not turning on would have such a drastic effect? - (realise this is potentially a stupid question but i knew to bike mechanics)
  4. Coolant comes in a wide variety of colours so the red could be normal if the overflow reservoir was topped up recently with a different brand. Though that said if you don't know when the coolant was last changed then it'd pay to do it now. If the radiator hoses look to be the originals (in that they're so hard they're on the verge of fossilisation) then it's a good opportunity to do those to - rather than wait for them to fail at the most inopportune time.

    As for the fan it definitely serves a purpose as although the GPX is a small engine it does seem to get hot quick without decent airflow. I've had mine nudge very close to the red zone on the temp gauge when held up in traffic (ie school zones, roadworks, etc.) - and that was with the fan going flat out. In contrast the fan on my old 250 Katana turned on maybe once or twice in the entire time I owned it, which is one of the advantages of a naked (though on the plus side sitcking your hands on the engine block of the GPX when stopped at lights is almost as good as having hand warmers :)).

    If the switch isn't talking to the fan I'd suggest it's probably a dirty/corroded electrical connection - a pretty common thing on Japanese bikes of that age.
  5. Thanks again jd. I took the switch out and tested it in both boiling water and flame while checking to see if the current was switching on, (sparky mate had a gizmo). It's fooked

    Will definitely flush and check hoses.

    Thanks again
  6. Just an update - Put the new Thermo fan switch in and all systems are go - running lovely (for now) Thanks for all the tips.
  7. okay, I've replaced the thermo fan switch and the fan in running. replaced the coolant with the proper mix and took her for a nice long highway ride.

    It's not over heating but its running hot - a few degrees off the dreaded 'RED H'.

    when i pull up i hear bubbling in the reservoir :(

    Water pump is working as i can see it pumping with the radiator cap off so I'm guessing its the actual thermostat???

    any advice would be great.

    Thanks in advance!
  8. OK - the saga continues.

    Have replaced the thermo fan switch and its working.

    Have replaced the thermostat and it seems to be working.

    No overheating now but after a decent ride when I pull into the driveway i hear the overflow bubbling and a little bit of coolant comes out the overflow.

    Overflow seems to rise and lower how it should when I test it over short rides.

    I have checked all hoses and they all seem fine.

    Run and topped up several time to get all the air out.

    I completely stumped :(.

    Going to try another flush with some de-scaler tomorrow.

    Can anyone else suggest what I should try apart from selling it for parts !
  9. Good to hear it was only a switch. Last year while on a ride up lake mountain in Vic a new riders gpx250 did the same thing and turned out to be the same issue as yours. Must be a common problem with the old gpx's. His was a 90 bought off eBay for $1000 on the road.