Water conducts heat more effectively than antifreeze, so the mix should be 50-50. I was just wondering if years of topping off with undilute antifreeze could have reduced the heat transfer capacity of the coolant and thereby reduced heating capacity. As for the coolant overflow tank cap, I'm told th...

Thanks Matt. I just had the coolant tested and it came up ready for 50 below in upstate NY. Is that too much? Also, I have the old gray cap. Perhaps I should pick up the green one.

This began with a low coolant light on my 96 850 GLT. When I checked the overflow tank, I noticed a ring of crud around the opening after removing the cap. The level was just barely triggering the warning lamp on turns. I topped the fluid, but am now experiencing low heat from the climate control sy...