Coolant system air lock and emptied header tank
Discussion
Hello all. Still new to this mechanic stuff so have a quick query.
As well as other things, my fiancee had her coolant temp sensor on her Polo changed by a VW garage. After picking the car up and driving for about 10 - 15 minutes her coolant level light started flashing.
Got the car home and I inspected under the bonnet. It looked like the header tank had nearly emptied itself of coolant.
We called said garage up, chap came out and told us it was just an air lock so he topped the coolant up. He was quite apologetic (as coolant was in the engine bay, not the tank) and said it had simply cleared itself via the header tank cap. Apparently, it should have been picked up on his test drive.
Thinking about it logically, this makes sense. However, is this normal and does it seem like this is what has happened? I guess the only way to check is to keep an eye on the coolant and make sure the level stays ok.
Thanks all.
As well as other things, my fiancee had her coolant temp sensor on her Polo changed by a VW garage. After picking the car up and driving for about 10 - 15 minutes her coolant level light started flashing.
Got the car home and I inspected under the bonnet. It looked like the header tank had nearly emptied itself of coolant.
We called said garage up, chap came out and told us it was just an air lock so he topped the coolant up. He was quite apologetic (as coolant was in the engine bay, not the tank) and said it had simply cleared itself via the header tank cap. Apparently, it should have been picked up on his test drive.
Thinking about it logically, this makes sense. However, is this normal and does it seem like this is what has happened? I guess the only way to check is to keep an eye on the coolant and make sure the level stays ok.
Thanks all.
Some cars have bleed points on the cooling system to let the air out, others you just have to let it work its way out. I'd keep an eye on the header tank as if it keeps doing it you might have a head gasket problem, but it sounds to me like they just didn't run the engine long enough after changing it.
You can try to bleed the system yourself as it's a simple process.
With the engine cold, remove the cap from the expansion tank and set the heater control inside the car to hot.
Next, fire the engine up and let it idle for a few minutes until it warms up... don’t be alarmed if the level of coolant drops inside the expansion tank after a while as this is a natural result of the thermostat opening when the engine/coolant reaches temperature.
You’ll find a load of air bubbles will come out of the coolant – this is the system bleeding itself. You can also try to squeeze all the rubber coolant hoses as this may encourage the trapped air to come out (be VERY careful of any moving belts or fan blades etc if you do this with the engine running).
After the air has stopped bubbling up your system should be fine and you can replace the tank cap, but you may want/need to repeat the process a couple of times until you are happy... some cars are easier to bleed than others, especially if there is a bleed valve or screw (my girlfriend’s V70 is a swine to get right, for example).
DON’T remove the expansion tank or radiator caps when the car is hot as the cooling system is pressurised and you’ll get a face-full of scalding hot water – not nice.
With the engine cold, remove the cap from the expansion tank and set the heater control inside the car to hot.
Next, fire the engine up and let it idle for a few minutes until it warms up... don’t be alarmed if the level of coolant drops inside the expansion tank after a while as this is a natural result of the thermostat opening when the engine/coolant reaches temperature.
You’ll find a load of air bubbles will come out of the coolant – this is the system bleeding itself. You can also try to squeeze all the rubber coolant hoses as this may encourage the trapped air to come out (be VERY careful of any moving belts or fan blades etc if you do this with the engine running).
After the air has stopped bubbling up your system should be fine and you can replace the tank cap, but you may want/need to repeat the process a couple of times until you are happy... some cars are easier to bleed than others, especially if there is a bleed valve or screw (my girlfriend’s V70 is a swine to get right, for example).
DON’T remove the expansion tank or radiator caps when the car is hot as the cooling system is pressurised and you’ll get a face-full of scalding hot water – not nice.
Faust66 said:
You can try to bleed the system yourself as it's a simple process.
With the engine cold, remove the cap from the expansion tank and set the heater control inside the car to hot.
Next, fire the engine up and let it idle for a few minutes until it warms up... don’t be alarmed if the level of coolant drops inside the expansion tank after a while as this is a natural result of the thermostat opening when the engine/coolant reaches temperature.
You’ll find a load of air bubbles will come out of the coolant – this is the system bleeding itself. You can also try to squeeze all the rubber coolant hoses as this may encourage the trapped air to come out (be VERY careful of any moving belts or fan blades etc if you do this with the engine running).
After the air has stopped bubbling up your system should be fine and you can replace the tank cap, but you may want/need to repeat the process a couple of times until you are happy... some cars are easier to bleed than others, especially if there is a bleed valve or screw (my girlfriend’s V70 is a swine to get right, for example).
DON’T remove the expansion tank or radiator caps when the car is hot as the cooling system is pressurised and you’ll get a face-full of scalding hot water – not nice.
Thanks for that. With the engine cold, remove the cap from the expansion tank and set the heater control inside the car to hot.
Next, fire the engine up and let it idle for a few minutes until it warms up... don’t be alarmed if the level of coolant drops inside the expansion tank after a while as this is a natural result of the thermostat opening when the engine/coolant reaches temperature.
You’ll find a load of air bubbles will come out of the coolant – this is the system bleeding itself. You can also try to squeeze all the rubber coolant hoses as this may encourage the trapped air to come out (be VERY careful of any moving belts or fan blades etc if you do this with the engine running).
After the air has stopped bubbling up your system should be fine and you can replace the tank cap, but you may want/need to repeat the process a couple of times until you are happy... some cars are easier to bleed than others, especially if there is a bleed valve or screw (my girlfriend’s V70 is a swine to get right, for example).
DON’T remove the expansion tank or radiator caps when the car is hot as the cooling system is pressurised and you’ll get a face-full of scalding hot water – not nice.
Don't worry, I won't do it when hot.
What does setting the heater to hot do to help? Thanks.
Opens the circuit to allow the coolant to flow everywhere.
When doing my partners meriva it takes about 20 minutes of idle/3k revs to get all the air out after a full flush and change. XM needs a cut about squash bottle or similar as the top of the system is the top of the header tank, so needs extra lift to bleed properly.
When doing my partners meriva it takes about 20 minutes of idle/3k revs to get all the air out after a full flush and change. XM needs a cut about squash bottle or similar as the top of the system is the top of the header tank, so needs extra lift to bleed properly.
funkyrobot said:
What does setting the heater to hot do to help? Thanks.
As Beko said, setting the heater to ‘hot’ opens valve/s to the heater matrix (a kind of mini radiator which your fan blows air over transferring heat from the coolant system into the car interior), which allows coolant to circulate throughout the whole system and thus reduces the risk of any pesky air bubbles being trapped in the matrix itself.Obviously, this doesn’t effect the air con (if fitted) just the ‘normal’ car heater system.
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