Coolant Disappearing

[LoganB16]

Hi I understand similar threads have been posted however not exactly the same, wondering if anyone can help. So I have a 2.0 Seat Leon FR TDI (2014) I seem to have an issue when the car is off the coolant seems to mysteriously disappear without any leaks however I do hear water moving in the dash when the car is off. additionally 75% of the time if I release the expansion tank lid to fill it when air shoots out some of the coolant returns to the expansion tank from thin air. I have no milky oil , oil has been recently changed less than 1000 miles ago and no indication of an issue I’ve also had the radiator and expansion tank replaced as we thought that could’ve been the issue as the radiator did have a leak?

thankyou

 

[Tell]

Hi I understand similar threads have been posted however not exactly the same, wondering if anyone can help. So I have a 2.0 Seat Leon FR TDI (2014) I seem to have an issue when the car is off the coolant seems to mysteriously disappear without any leaks however I do hear water moving in the dash when the car is off. additionally 75% of the time if I release the expansion tank lid to fill it when air shoots out some of the coolant returns to the expansion tank from thin air. I have no milky oil , oil has been recently changed less than 1000 miles ago and no indication of an issue I’ve also had the radiator and expansion tank replaced as we thought that could’ve been the issue as the radiator did have a leak?

thankyou

You'd think you would see where it was going. Water in a diesel engine isn't good. I did have a petrol engine many years ago where it did escape into the engine. Those bolts not tightened down. Running on steam. A Fiat could take that and didn't suffer consequences a diesel it would write the engine off, as I understand it. Always taken an interest in this subject after the vanishing radiator water in my old Uno.

If the water doesn't return to the radiator and can't been seen and hasn't evaporated it feels like it's gone into the engine but you aren't seeing it as such. May be a blockage in the radiator. We need an expert .

 

[LoganB16]

You'd think you would see where it was going. Water in a diesel engine isn't good. I did have a petrol engine many years ago where it did escape into the engine. Those bolts not tightened down. Running on steam. A Fiat could take that and didn't suffer consequences a diesel it would write the engine off, as I understand it. Always taken an interest in this subject after the vanishing radiator water in my old Uno.

If the water doesn't return to the radiator and can't been seen and hasn't evaporated it feels like it's gone into the engine but you aren't seeing it as such. May be a blockage in the radiator. We need an expert .

I’d imagine so, I take it the water sound is the sound of the coolant as seat does have the heater matrix and it’s complicated coolant system round there.

 

[LoganB16]

You'd think you would see where it was going. Water in a diesel engine isn't good. I did have a petrol engine many years ago where it did escape into the engine. Those bolts not tightened down. Running on steam. A Fiat could take that and didn't suffer consequences a diesel it would write the engine off, as I understand it. Always taken an interest in this subject after the vanishing radiator water in my old Uno.

If the water doesn't return to the radiator and can't been seen and hasn't evaporated it feels like it's gone into the engine but you aren't seeing it as such. May be a blockage in the radiator. We need an expert .

But is weird how the expansion tank can be empty and just by realising cap that Inturn releases pressure that coolant just appears from wherever it’s disappearing to

 

[Compo1]

But is weird how the expansion tank can be empty and just by realising cap that Inturn releases pressure that coolant just appears from wherever it’s disappearing to

I'd say since you have had the radiator and expansion tank replaced, you now have air in the system. More or less confirmed by the noise behind the dash.

That could also be a sign the heater matrix is blocking, if it is your drivers side vent will be significantly cooler than the passenger side vent.

Before you go any further, take it to a garage assuming you don't have a compressor and vacuum filler and ask for a coolant flush and insist the system is refilled under vacuum, these coolant systems have a habit of trapping air in them and it is very difficult to get out with old school conventional methods.

 

[LoganB16]

I'd say since you have had the radiator and expansion tank replaced, you now have air in the system. More or less confirmed by the noise behind the dash.

That could also be a sign the heater matrix is blocking, if it is your drivers side vent will be significantly cooler than the passenger side vent.

Before you go any further, take it to a garage assuming you don't have a compressor and vacuum filler and ask for a coolant flush and insist the system is refilled under vacuum, these coolant systems have a habit of trapping air in them and it is very difficult to get out with old school conventional methods.

Ok thankyou will do that they did say they flushed the system however will try this, one weird thing is it didn’t do for about 2 weeks after having tank replaced then came back yesterday did it consistently all day and this morning and then this afternoon and evening it’s stopped doing it again?

 

[Compo1]

Ok thankyou will do that they did say they flushed the system however will try this, one weird thing is it didn’t do for about 2 weeks after having tank replaced then came back yesterday did it consistently all day and this morning and then this afternoon and evening it’s stopped doing it again?

How they filled it and bled the system is the important part here, lots of garages still use old school methods of burping the pipes with the heater on high it is just not good enough on these complex systems which is essentially three cooling systems in one.

The correct method is vacuum filling, which should remove all the air before fluid is sucked back in under vacuum done correctly no air should be present. But to be sure it should then be bled with a procedure via VCDS or similar, this will open all the 3 cooling system to allow any trapped air out.

 

[LoganB16]

How they filled it and bled the system is the important part here, lots of garages still use old school methods of burping the pipes with the heater on high it is just not good enough on these complex systems which is essentially three cooling systems in one.

The correct method is vacuum filling, which should remove all the air before fluid is sucked back in under vacuum done correctly no air should be present. But to be sure it should then be bled with a procedure via VCDS or similar, this will open all the 3 cooling system to allow any trapped air out.

Oh okay awesome that’s extremely helpful I’ll speak to them and get something sorted thankyou, question tho surely if it’s air pockets that are filling up does that mean the coolant is still in the system it’s just not circulating the car correctly ?

 

[Compo1]

Oh okay awesome that’s extremely helpful I’ll speak to them and get something sorted thankyou, question tho surely if it’s air pockets that are filling up does that mean the coolant is still in the system it’s just not circulating the car correctly ?

Well no, and at working pressure when the car is hot coolant levels will drop because the air gets compressed with coolant, that the main reason the coolant disappears then returns when you release the pressure.

 

[Tell]

Well no, and at working pressure when the car is hot coolant levels will drop because the air gets compressed with coolant, that the main reason the coolant disappears then returns when you release the pressure.

Mine just went into the engine all those years ago blowing steam out the back exhaust . The garage hadn't tightened the block down after skimming engine. Father (ex WW2 flying boat flight engineer) said tell your garage to tighten the engine up properly next time... he knew about engines. Eventful trip up the M1 with steam. Diesel it would have written it off.