Coolant expansion tank-something loose inside ?

[Ringsby4]

I removed the expansion tank to give it a clean,was heavily discolored.As I picked it up and turned it over,something in the center chamber moved and made a gentle thump.It sounds like a wad of something-soft ? Whatever it is,its free to move within that chamber.Maybe 2 by 1 inch,hard to say. I gave the tank a soak in hydro acid and a lot of sediment released and holding the tank up towards the sun I can just make out maybe a triangular shape and I am sure I can see a hole in each corner.The center chamber can't be accessed.Looks like the tank has never been removed. I'm giving it another soak in a stronger solution and I'll have look again.Weird.

[DrGER]

Maybe a packet of desiccant in the center chamber ?

Our '14 threw a "low coolant" IC warning 6-8 months ago, so I got a spare Febi Bilstein part, just in case. The Febi part has a packet of something in that center chamber. The original expansion tank is still OK after the original warning since jiggling the coolant sensor level wires. --g

[Ringsby4]

Maybe a packet of desiccant in the center chamber ?

Our '14 threw a "low coolant" IC warning 6-8 months ago, so I got a spare Febi Bilstein part, just in case. The Febi part has a packet of something in that center chamber. The original expansion tank is still OK after the original warning since jiggling the coolant sensor level wires. --g

It is a sachet.The bottle is totally clean now ( hydro acid,the concreters friend ! ) and I can clearly see it,but desiccant-I thought that was used to absorb moisture,this is in a flooded chamber.The sachet has come loose as I can also see a little partition moulded into the chamber which I can only presume is to contain it.
But what's in that evil little package ?

[Smac770]

If it's a packet of stuff, it's a silicate packet. Dissolves over time to keep the silicate levels up in the coolant as it ages apparently.

[Ringsby4]

If it's a packet of stuff, it's a silicate packet. Dissolves over time to keep the silicate levels up in the coolant as it ages apparently.

Really ? Thanks ,you really are a mine of knowledge - Cheers from Australia !

[Ringsby4]

Next issue is my coolant level sensor doesn't seem to be working.I'm curious how it works given that the 2 probes come up from the bottom.The tops of the two separated probes coincide just below the low mark.
Makes sense.What doesn't make sense is that these probes are continuously immersed because they come from the bottom of the tank and should/could be closing a circuit all the way up .I could understand if they came down from the top of the tank then bridged the circuit just on reaching the low point and created the warning.Eyeballing them ,they seem to be made of the same material.What is so special about just the tips so only these create the trigger ? What am I missing here ? Smac770 ?

[Smac770]

Never seen a pic of the level sensor in the coolant tank. It'll be a float with switch or a 2-prong style. I know people have mentioned the one in the windshield washer tank is a 2-prong style. That's why the Rain-X fluid coats it and creates a conductivity issue that gives a false warning. The prongs are not exposed the entire height, only at the tips. So when the fluid level drops below the exposed tips, then there's no more conductivity and the control module sees an open circuit. If the prongs appear exposed the entire height, there's probably some coating that's clear on them or such. Would need to tear one out of a reservoir to really see.

[silver_tt]

Yes it's a silica packet (which is a silicate if you want to get technical). Not evil, just leave it in there.

Don't understand the question about how it works. The probes are immersed, when they are not the voltage will change which the ECU will pickup in real time (if the voltage increases or decreases doesn't matter if the ECU knows how it works, which it does). Just replace the entire coolant reservoir. They need to be replaced every ~100K miles on these engines anyway due to the heat cycling compromising the integrity of the polymer.

[Ringsby4]

Thanks both,explains the situation with the sensor,I get it now.I'll have a jiggle with the plug on the base however I noticed some green corrosion on one of the pins so has been some moisture there.The genuine coolant tank is reasonably priced over here from a reseller at $A105 so I think I'll probably just grab one.

[Ringsby4]

New coolant tank arrived,now installed with fresh coolant.All good except still no low level warning.It has worked in the past,last year when I had a leak in the radiator.I looked at the socket and I can see some corresponding green to where the seep was in the pin housing ( my post above).Sprayed Inox and tried a tiny flat screwdriver in an attempt to clean the socket bearing surfaces.Obviously had no luck,still no warning.
Is there any brutal chemical to clean off the verdigris- hydro acid ? haha not wholesale,I could use a pipette,apply one drop and gently compressed air blast it out then Inox again..? Any suggestions appreciated !
EDIT: so,did a backyard experiment and found some copper wire with verdigris and yes,hydrochloric acid cleans it to bright finish.I then applied a drop in the socket,yes cleaned it and then flushed with Inox and blew out with compressed air-nothing,no warning.
I'm wondering if VCDS might show the omission of the warning as a fault ( just don't have it here atm )

[Ringsby4]

Wondering where I can go from here to get the warning working.The original pump is still installed but may fail as they do,I feel I need some pre warning.Unlike some of the warning lights which show when ignition is on but not started,this warning doesn't.

[Smac770]

If you pull the plug, do you measure voltage across the pins on the harness plug?
With the tank full and with the tank empty (best as can be now that it's installed), what resistance do you measure across the pins on the reservoir socket?
Maybe either there's no voltage making it there, or there's no resistance change occurring.

There could be a short between the two wires.
If you measure the voltage from each harness plug pin to the positive jump start post, one should read 0V and one should read 12V (I'm assuming the control module is applying 12V and not something lower like 5V).
Then if you measure the voltage from each harness plug pin to the negative jump start posts, again, one should be 0V and one 12V, but which harness pin reads which should be inverted.

[Ringsby4]

If you pull the plug, do you measure voltage across the pins on the harness plug?
With the tank full and with the tank empty (best as can be now that it's installed), what resistance do you measure across the pins on the reservoir socket?
Maybe either there's no voltage making it there, or there's no resistance change occurring.

There could be a short between the two wires.
If you measure the voltage from each harness plug pin to the positive jump start post, one should read 0V and one should read 12V (I'm assuming the control module is applying 12V and not something lower like 5V).
Then if you measure the voltage from each harness plug pin to the negative jump start posts, again, one should be 0V and one 12V, but which harness pin reads which should be inverted.

In retrospect I should have measured the resistance on the new reservoir compared to old but in my hurry to get it installed,I was caught assuming it would just work correctly,ha !
I'll check the voltages as you suggested,thanks