Extra coolant tank?

[dictys]

My car seems to have a extra coolant tank situated in the boot opposite side to the battery hidden by carpet. I can't find what this is for, it has a hose disappering into passenger side rear quarter. It does not get hot and the liquid does not look like water, can't reach in to dip the liquid? The liquid inside is below the coolant level marked on the tank.

Any ideas?

Rgds
Dictys

[LOTUSUSA1]

Does it appear to be connected to the overflow cannister for your coolant?

[Del-Esprit]

Not sure what model you have, but on my 95 S4s this sounds like the coolant expansion tank.
Normally this is filled to about half way with coolant/water mixture. The esprit is a presurised coolant system and as pressure builds up it may need to vent somewhere rather than blowing hoses. I believe this tank is designed to catch the release and any water and then allow water back into the main tank if a vaccum is created on cool down.

Not sure on the vaccum return but mine certainly rises and lowers during heatup cool down cycle.

[MikeyRide]

Del is right. In theory, the main tank is always filled to the top and expansion/contraction is handled by the overflow tank. In practice, the main tank doesn't draw very well on cooldown and tends to have a static cold level a couple inches below full.

[cnh1990]

That is the location of the coolant expansion tank connected to the header tank on the right rear of the engine bay. It is connected to the larger of the two header tanks. On SE's the chargecooler system is seperate from the regular cooling system. I sort of like this feature.

You will a black hose from the larger header tank go around the front of the engine compartment then through the trunk wall on the left to the white plastic expansion tank covered with a velcro carpet cover. Another hose then exits the tank to right behind the left wheel well through a penetration through the floor of the trunk next to the expansion tank. Any excess coolant will exit at this spot.

A bit peculiar place for the overflow and it has mystified more than one person when coolant is found on the garage floor under the left rear tire.

I add coolant using a small plastic bottle with a 50/50 mix.

Calvin 90 SE