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Thread: Thermostat - totally confused!

  
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    Question Thermostat - totally confused!

    Had all the symptoms of a dead thermostat i.e.
    Coolant temp gauge off the bottom of the scale while driving on fast road.
    Temp comes up to normal eventually [only] when stopped or driving slowly.
    So, I got one of the one of the ones that goes in the radiator top hose from the bloke who sells them with a hose clip for the 8v engines. Fitted the new thermostat and as it was cold, it was firmly shut.

    Took it out for a long drive today the symptoms had not changed AT ALL!

    I am totally confused how the engine can massively over-cool with two thermostats fitted, one of which is brand new and was shut.

    How can this happen?
    Where is the coolant temp sensor, could it be being cooled by the air flow?
    03 1.6 8v Astra Estate (Auto)

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    A (very) long shot!

    Is there any way the flow in the cooling system could be reversed? Can the water pump be put in wrong?

    It the system was flowing backwards, it could overpower the spring in the [healthy] thermostat and constantly put flow through the radiator. Voilà, over-cooling with a healthy thermostat or two...

    A backwards thermostat could give the same effect, but I'm sure I put the new one in right i.e. the copper temp sensor bit towards the old thermostat and engine block as per the instructions supplied.
    03 1.6 8v Astra Estate (Auto)

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    not really mate the pump is driven off the belt so can only go one way. but tbh it sounds ok.mine barely goes past 80 when driving in this weather and then will go up to 90 sitting in still.take it out and put it in boiling kettle water and check it opens on the temp its supposed to,also have you got the right thermostat??

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    Quote Originally Posted by mossy88 View Post
    not really mate the pump is driven off the belt so can only go one way. but tbh it sounds ok.mine barely goes past 80 when driving in this weather and then will go up to 90 sitting in still.take it out and put it in boiling kettle water and check it opens on the temp its supposed to,also have you got the right thermostat??
    Thanks
    The temp is not just a bit low, it is literally off the bottom of the scale while driving on main roads. The needle comes up to vertical when sat still for a few minutes or in slow stop/start traffic, but falls off the scale again when back on the open road.
    The thermostat is the one supplied to all the other Vauxhall 8v engine users here (Renault 89 deg C I think) who have bought this 'repair kit'.
    03 1.6 8v Astra Estate (Auto)

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    im not sure where by its located mate but have you replaced it for a new one?? and if you have put the new modded one on it then do have you put it on the right way?

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    Temp gauge under-reading????

    I took the new t-stat out, it was cold/shut; boiled it in a pan of water it opened and shut again on cooling. So I think it is ok.

    Refitted it and ran the car for a while; it all seemed fine i.e. rad hoses stone cold while the other hoses and fluid were warming up nicely.

    THEN! When the temp gauge was still well below 80, the t-stat was starting to open! It seemed to be well open with the temp gauge still showing under 80.

    I AM STARTING TO THINK THAT IT IS ALL JUST AN UNDER-READING TEMPERATURE GAUGE! Must be under-reading by 20 deg C or more.

    Anybody tell me what temp the electric fan should cut in?

    I am now off to buy a thermometer to see what temperature the coolant really is...

    UPDATE: Bought digital thermometer, was trying it out, coolant boiled, thermometer got wet - buggered! That was a quick way to waste £10!!
    03 1.6 8v Astra Estate (Auto)

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    Quote Originally Posted by smssms View Post
    I AM STARTING TO THINK THAT IT IS ALL JUST AN UNDER-READING TEMPERATURE GAUGE! Must be under-reading by 20 deg C or more.
    But then that would mean when the gauge says 90c in traffic, the engine is actually at 110c.

    On a Zlet the fans come in at around 92c, assume most MK4's are the same??

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    How is this possible?

    This is really annoying me now...

    Can anybody explain how a petrol engine with a working thermostat can be running off the bottom of the temperature scale in normal a-road/motorway conditions?

    The thermostat cuts the radiator out of the loop, how on earth can air flow over the engine block send the whole engine temperature off the bottom of the scale?

    I've owned and driven a lot of cars over the years and never seen this before. Anything like this in the past was instantly cured by a new thermostat.
    03 1.6 8v Astra Estate (Auto)

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    Air lock in the coolant system? My FIL's Zafira appears to have had this after a new waterpump. Fine straight after, within a week it wasn't blowing hot through the heaters, topped up with well over 1 litre of water and so far so good.

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    The coolant is not low and I don't think there is an air lock...

    The heaters are blowing hot (even at speed when the temp gauge is of the bottom of the scale). I only had a medical thermometer that went up to about 41 deg C and the heater blowers were putting out a higher temp than that!

    Everything seems ok apart from the fact that the temp gauge drops off the bottom of the scale at speed (but is fine when not moving or stop/start driving) - How can this happen?
    03 1.6 8v Astra Estate (Auto)

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