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Thread: Replaced Thermostat - some advice please.

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    Default Replaced Thermostat - some advice please.

    Hi All,

    After noticing that my Signum 2.0DTi was taking longer to warm up and the temp gauge was being a little eratic, and not staying at a constant temperature; I decided to replace the thermostat.

    Just finished the job, using a genuine GM stat & housing and it doesn't seem to have made any difference

    The temp gauge did get up to around 87C at motorway speed, but then fell back again at normal road speeds to around 80C. Back at home, it fell back to 0C!!

    Any thoughts or advice as to what to check next, could it be the coolant temperature sensor?

    Thanks for any Help,

    Colin

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    87C on the motorway implies that the stat was working fine, otherwise it would drop when on the motorway.

    Sounds like it was fine, and has now seized open again!

    Is the coolant still clear, and did you flush out the system? May be a small blockage in there somewhere

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    Airlock possibly, or a duff CTS.

    Did my Stat in November, never reaches above 85 on the gauge and appears to take a while to warm up. Did a session with opcom to see the temp it was reading, and measured it with a temperature probe. Got 90 on the probe, and 82 on opcom. Temp sensor is faulty, just one of those things i havn't got round to doing yet lol

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    Hi Tony,

    Thanks for the reply, I didn't flush out the system; but the coolant didn't appear to be all that cloudy from what I saw. Looking at the old thermostat; it doesn't appear to have failed open either. A little confused at the moment, do you think it's ok to still be driving it??

    Wondering if there could be an air lock in there somewhere, perhaps in the sensor area??

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    Thanks also Mr Derv, perhaps i'll whip out the CTS and see if it releases any trapped air. Am i right in assuming the CTS is the one located above the Thermostat housing itself on the Y20DTH engine?

    Been having a quick look, and think the CTS part number is 90541937, does that seem right?

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    Did you bleed the system after fitting the new thermostat? If you lost any coolant during the fitting process - or indeed if you drained any beforehand - then air will have replaced that coolant and you need to remove that air and put more coolant in.

    If you didn't bleed it, then start with a cold engine, take off the coolant bottle's cap, start the engine and watch the coolant level drop as air is expelled and replaced with coolant. Keep topping up the coolant bottle to the MAX marker. You'll need to put the bottle's cap back on before the engine gets hot though, or coolant will start spurting out.

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    Hi Rebellion,

    Did loose some coolant when removing the old thermostat and hoses. Once all was connected up, I removed the cap from the expansion tank; started the engine and re-filled the system to the max cold level.

    Carried on watching levels and topping up if required for approx 10mins at idle speed whilst checking for leaks. Once happy there was no leaks took the car out for a run, for approx 15 - 20mins.

    Is there another way to bleed the system? I was under the impression that it self bled

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    Sounds like you did it correctly, but it's worth doing it once more, starting with a cold engine again.

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    Quote Originally Posted by colreid View Post
    Thanks also Mr Derv, perhaps i'll whip out the CTS and see if it releases any trapped air. Am i right in assuming the CTS is the one located above the Thermostat housing itself on the Y20DTH engine?

    Been having a quick look, and think the CTS part number is 90541937, does that seem right?
    Yep, it's above the thermostat, not sure on the part number though

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    Thumbs up Quick Update

    Just tried bleeding the system again for 20mins at idle speed. Didn't really notice any air being expelled or the coolant level dropping. Temp gauge hadn't moved during that time either, so I wasn't really holding out too much hope.

    Took the Signum out for another run for about 30mins, on a mixture of roads and motorway. Low and behold the temp gauge went to approx 87C on the roads, and remained there on the motoway; with no dropping at lights or when back at home.

    Was still watching the gauge like a hawk the whole time though!!

    Looks as though the problem was an air lock as suspected by you guys.

    As usual, a great forum; I wouldn't have attempted the job if I hadn't seen the how 2, and then had some good advice to try and sort the last issue.

    Will still keep an eye on it during my commute though.

    So thanks for the help guys, much appreciated.

    Colin

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