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    cooling system pressure

    Hi! can someone tell me how many bar or psi pressure is normal in the cooling system when the engine is warm? (if the thermostat is open) for cooling water above 90 degrees Celsius? (petrol turbo 850 v70 s70)

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    Quote Originally Posted by dublin19 View Post
    Hi! can someone tell me how many bar or psi pressure is normal in the cooling system when the engine is warm? (if the thermostat is open) for cooling water above 90 degrees Celsius? (petrol turbo 850 v70 s70)
    A stock car running stock Expansion cap would see between 10-13psi once up to normal running temperature.

    Remember pressure comes from the expansion of the coolant NOT the pump. If you have access to a 'cooling system pressure tester' then you can remove the expansion cap and fit the gauge. Start the engine cold and the needle should not move...should remain on '0' psi.
    As the engine slowly warms up you should see the pressure slowly increase in direct correlation with engine temperature, with no spikes or surges or sudden rises.

    Once the engine coolant pressure reaches around 5 - 6 psi, this is a good time to check the operation of the water pump.
    Have one of your servants blip the throttle to around 3500 rpm. You should see the pressure gauge either rise (positive) or fall (negative) and then return to 5 - 6 psi. This is Normal and indicates normal operation of the WP. The reason the gauge will either drop or rise will depend on whether the gauge is on the positive side or negative side of the WP.

    Once at optimum temperature (87-90*C) the thermostat should be open fully and all hoses will be hot. Using a thermoprobe will give you a more accurate reading, but not required.

    There should be around a 10 degree difference between top hose and bottom hose and the same on the heather matrix. This is normal and indicates the cores of the Radiator and heater matrix are not blocked.

    At around 104*C the cooling fans should start to kick in, stage 1, 2, 3 and so on. At this point, thermal pressure should not exceed the maximum (around 13-15Psi) and the cooling fans should cycle on/off as normal.

    This is the correct method for checking a cooling system functions.

    If you have access to diagnostics with live data, then it's always a good idea to pull up the coolant temperature reading, as you can then verify the temp sensor operation in relation to the temp gauge inside the vehicle. Expect to see around 10*C +/- compared to the gauge as the sensor is always more precise.

    Hope this helps.
    Last edited by LeeT5; Saturday 7th September 2019 at 10:30.

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