[S6F]

As you face the B58 engine, to the right is the usual coolant reservoir. But directly in front of it is another, smaller one with a similar shape cap. The manual does not identify this reservoir, but inside there also appears to be a blue fluid like coolant. What is this and why is it a secret?

[XRAVE]

Originally Posted by stevefoster

As you face the B58 engine, to the right is the usual coolant reservoir. But directly in front of it is another, smaller one with a similar shape cap. The manual does not identify this reservoir, but inside there also appears to be a blue fluid like coolant. What is this and why is it a secret?

It's the coolant used for the air to water intercooler

[S6F]

Thanks, that makes sense. Don't you think BMW should mention this in their owner's manual, especially when the fluid level has to be topped off? Just sayin'.

[ajob]

My owner's manual states:

"The vehicle has two coolant tanks located in the engine compartment.

To guarantee operational safety of the vehicle, always check the coolant levels of both coolant tanks"

[S6F]

Never saw that. Was looking at the "under the hood" section with the diagram that points out all the key components. It shows only one reservoir. Does yours show two?

[ajob]

Yes, it shows two coolant tanks, one is for "charge air".

[ajob]

I re-read the post and submit my apologies, my manual is for the S63 engine, not the B 58.

Still, I assume it is safe to assume that your second coolant tank has the same purpose.