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Thread: Thermostat removal

  
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    Thermostat removal

    Hi all,

    I want to test the thermostat in my engine[1] but the Haynes manual says to drain the cooling system before disconnecting the hose covering the thermostat - I'd much rather not have to drain the cooling system - do I really have to drain it?

    Thanks very much for your advice in advance!

    [1] As it takes an age to warm up - sometimes when the air temp is 0 degrees C, it won't reach operating temperature even after a hour on the motorway, staying at 80 degrees C, and when the air temp is about 5 degrees C, it won't reach operating temperature until after 15 minutes, but can drop down fast when I hit a cold air pocket on the motorway.

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    paul.spencer's Avatar
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    It does rather sound like your thermostat is stuck open. A new thermostat can't be too expensive. Why not just drain the old coolant, flush the system thoroughly and install a brand new genuine Vauxhall thermostat...

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    Don't have a hose, so can't flush the system. Would rather double check the thermostat is really broken, as some people tell me the Y17DT engine does take 10 minutes to reach operating temp....

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    Well it is supposed to be a 92 degree thermostat and you describe 80 degrees after an hour on the motorway - that would suggest that something is wrong. I guess it is possible that the gauge isn't reading correctly - do you get hot air from your heater?

    If your heater is working but the gauge still says only 80 degrees then maybe you thermostat is OK and its a gauge or temp sensor problem, although with your engine I would have thought a faulty coolant temperature sensor might affect how your engine runs.

    Normally you should be able to idle the engine and see the temp rise up to and beyond 92 degrees. Even in winter (unless maybe its seriously freezing out) if its sitting in your driveway or on the street idling with no wind over the radiator I would think it should heat up enough to get the fan going.

    Anyway, if it looks like the thermostat is not working and you don't have a hose and can't do a cooling system flush etc, don't see how you could test the thermostat so maybe best just to bring your car in to a garage or somewhere they can do it all for you.

    --------------------
    p.s. Hey I just realized that you say it can/does reach operating temp was just thinking - I have read posts about people blocking off part of their radiator because they reckon the system is overcooling in winter conditions - don't know if it applies to your situation but its something to consider....

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    Yes I get hot air from the heater. When I shut off the heater, it goes back to 87 degrees C. I've never ever seen the gauge go over 90 even when stuck in the traffic at the hottest day of the year.

    The reason why the engine don't get to its operating temp after a hour is because I use the heater. If I turn it off, it goes get up to its operating temp, but I freeze, so I turn it back on, and it drops back to 75-80 - that's only if it's below freezing outside. If it's normal outside, it hovers at about 85 until I turn off the heater. As the gauge shows exactly the expected behaviour when I mess around with the heater, it leads me to think that it's operating just fine.

    As my car's aerodynamics have been modified by Vauxhall at the factory, it is possible that the engine isn't loaded hard enough and isn't producing enough heat to heat up the cast iron block. After all, I do get 80 MPG on the motorways. But I just want to double check the thermostat is really working, as a cold engine uses up a lot of fuel. If it definitely involves draining the cooling system, I might as well take it to a garage anyway. I think the coolant probably need replacing by now too.

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    Just replaced the stat on my y17dt. car was not getting hot enough to show on the gauge although the heater was ok(ish) Gauge now gets up to 88c and heater is excellent. Tested the old stat and found it was opening slightly at 70c. it was only 6 months old!! new one is a genuine vaux part and is stamped 89c

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    Quote Originally Posted by pewseyfam View Post
    Just replaced the stat on my y17dt. car was not getting hot enough to show on the gauge although the heater was ok(ish) Gauge now gets up to 88c and heater is excellent. Tested the old stat and found it was opening slightly at 70c. it was only 6 months old!! new one is a genuine vaux part and is stamped 89c
    Good info from someone with the same engine and similar problem. Interesting that the replacement thermostat is stamped 89C as the info I have it should be a 92C thermostat like on my old Astra.

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    I note I can get an OEM thermostat for £12 inc VAT exc postage. Is it worth changing the thermostat and antifreeze without flushing the system, or best get the old one checked out first? The antifreeze is almost certainly about 50,000 miles old, my hydrometer shows the yellow ball.

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    Quote Originally Posted by Eddles View Post
    I note I can get an OEM thermostat for £12 inc VAT exc postage. Is it worth changing the thermostat and antifreeze without flushing the system, or best get the old one checked out first? The antifreeze is almost certainly about 50,000 miles old, my hydrometer shows the yellow ball.
    I was going to say that it will be comforting to know that you have done your car a favour by flushing the system out and replace with new coolant and install new thermostat all in one go. You would be amazed at the crude that can come out even if the existing coolant looks in good shape. And I certainly wouldn't muck about with the old thermostat, I would would just install a new one...

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    As I mentioned before, I can't flush the system out. Is it OK for me to replace the thermostat and coolant without flushing, or is it worth paying a chunk extra to get it flushed at a garage?

    Thanks again for advice, much appreciated!

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