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Running without a thermostat

Discussion in 'Technical and Troubleshooting Torque' started by ogre, Jun 26, 2011.

  1. Let me set the scene here - I had discovered an apparent overheating problem with my ZZR 250. Recent on-site testing at Racer Replica showed the temp gauge flickered violently, but usually showing just off cold. All of a sudden, coolant spewed out from the expansion tank, with the gauge jumping up to half - plus the flicker. When she cooled down, a coolant levels check showed the radiator at full, and the expansion tank wanting a top-up. The suscpicious cooling system components wer the temp-gauge sender, the thermostat, and the head gasket.

    Well, when I removed the fuel tank and accessed the thermostat housing, I discovered a loose connector on the sender. Tapping the head of the connector tightened that up, and the temp gauge now speaks the truth.

    Without a thermometer, I tested the thermostat on the stove in boiling water. It took a heavily-bubbling boil for it to open, and then it only opened a little.

    Keeping the thermostat out, I have since reassembed the bike, filled and air-bled the coolant, and took it out for a putt. At speed, temperature leveled off just below 1/4. Hanging around a servo a while showed the temperature climbing up to half, then the thermofan kicked in to bring it down. That's much more like it, and it looks like I can rule out a bad head gasket.

    Now to pick everyone's brains. I have ordered a new thermostat, at factory spec to open 85-90deg. Meanwhile, apart from taking a little longer to warm up, does anyone know of any issues in running this carburettored ZZR without a thermostat for a while?
  2. should not be any, except for the whole heating to adequate temprature.
  3. Probably OK as a temporary measure but fit the new 'stat as soon as you receive it.
  4. It shouldn't hurt it but in extremes they tend to run hotter without the stat as the stat restricts the water flow and therefore it spends less time in the rad cooling...

    Probably not a problem in this weather.