Coolant level drop while idling

[Slugger]

Basically, when I start the car up the coolant is in between the min and max.

As it sits idling the level drops a good 3-4 inches. Right to the bottom of the coolant tank.

If I stop the engine and open the cap the level rises again?

Is this normal?

Or what is it thats causing this?

On all my old cars the level has stayed pretty constant?

 

[Slugger]

Any help is really appreciated!

 

[muddyboots]

Maybe you've got air trapped somewhere ?

 

[Slugger]

That was one of my thoughts but how do you get rid of it? I thought the kinda self bleed?

 

[andycupra]

so it sounds like no coolant is entering the expansion tank, but leaving it ok.
When you get it to rise by removing the cap i presume it rises from the bottom and not from the top pipe filling it?

Sounds like either air in the system, (although they normally self bleed) or a blockage somewhere, perhaps in the pipe that fills the expansion tank?

Any issues with the coolant temp? as it sounds like the coolant isnt circulating.

Have you tried running it with the cap off?

 

[andycupra]

also seen here:
http://www.seatcupra.net/forums/showthread.php?t=183119

 

[Slugger]

so it sounds like no coolant is entering the expansion tank, but leaving it ok.
When you get it to rise by removing the cap i presume it rises from the bottom and top from the top pipe filling it?

Sounds like either air in the system, (although they normally self bleed) or a blockage somewhere, perhaps in the pipe that fills the expansion tank?

Any issues with the coolant temp? as it sounds like the coolant isnt circulating.

Have you tried running it with the cap off?

I originally thought the coolant was returning from top filling pipe, but I would need to check. That would certainly suggest a blockage that meant coolant was leaving but not coming back.

The drive today the car overheat!! Grrr!!! Got really hot and looked like it was boiling the coolant!!

Will try it with the cap off and see what happens.

Thanks for the link, will check that out too.

Could it be the water pump?

 

[andycupra]

(the link is just to your other thread on the same subject..)

Funny i was just trying to get my head round whether it could be the water pump. Never say never, but it doesnt appear consistent with a water pump issue...

id definately run it with the cap off for a bit.... strange!

 

[muddyboots]

VAG water pumps are renowned for failing (either the plastic impeller breaks up, or spins loosely on it's shaft).
However - while that would account for the overheating, I can't understand why it would make the level drop.

I never did any work on my Ibiza's cooling system so don't know if they self-bleed or not. I know my Passat doesn't self-bleed, I have to partially slide a heater coolant hose off until it exposes a vent hole, then remove the expansion tank and lift it up to provide enough head to drive the air out.

FYI when my water pump went, the engine would cool OK under most driving conditions, but under heavy load it couldn't provide enough flow and it would overheat, and then boil if I didn't ease off and whack the heaters & fan on full quick enough

Just thought - might be worth turning your heaters up to full heat and drive round, to make sure you have got water circulating through the heater matrix circuit. Maybe there is air in there, and with the weather being warm you might have not have the heaters turned up enough to circulate it out.

 

[Slugger]

Tried the heaters and there is no heat?


So would that be consistant with the water not circulating. And the cause being the pump, ir block or some other bloackage?

 

[andycupra]

well that confirms the coolant isnt circulating, but then we knew this anyway. It may have helped clear any airlock but it would seen not in this case.

Anyone know where the thermostate is? this may well be stuck closed?

 

[Muttley]

Slugger, what engine?

Generally, on TDI's, the thermostat is in the block, mounted under the pipe that connects to the radiator bottom hose. It is right next to the water pump in the block, and below the diesel injection pump in TDI 90 and 110 installations. The position is the same on PD engines, but there is no injection pump in the way so it will be a bit easier to get to.

 

[Slugger]

Its the TDI 110.

Tried it with the coolant cap off but the level dropped just the same, although it did not come back up like when I took the cap off before. This makes me really worried as where is the water going!! There was some steam but not enough for the amount that went missing.

Scared it could now be the head gasket thats gone so gonna get a compression test done.

Will try and locate the thermostat and start there.

Anyway of knowing if the pump is working or not?

Thanks for the help guys

 

[jiege01]

would it have anything to do with the drop in pressure when the coolant lid is open. the release of pressure will draw the water upwards, as when the lid is opened when the engine is hot it hisses.

 

[Slugger]

would it have anything to do with the drop in pressure when the coolant lid is open. the release of pressure will draw the water upwards, as when the lid is opened when the engine is hot it hisses.

No I don;t think so as the coolant drops whether I have the cap on or off?

And you would normally expect the level to rise a little when hot not drop 3-4 inches