I did try a search, so sorry if it has been covered.

i have noticed that since the colder weather has hit (-20 celsius) that the hatch doesnt fully extend open without some help from me. it did it last year too, but wanted to wait til the summer to confirm. (they worked fine in the summer).

Question is, if i replace them now, will the same thing happen (ie due to cold weather) or will they work like summer??

Its a 2004, and as far as i can tell they are stock.

 

Have you tried applying some silicone lube on the strut shafts?

 

From the www.autopartsbylou.com web site in their FAQ section:

Q. My lift supports work great in the summer but are slowly losing their power.

A. Most supports thrive in the summer heat, and fail when the temperature begins to drop. The majority of the pressure ratings that we publish are determined at a temperature of 20 C or 68 degrees.

For every 10 degrees C output force either increases or decreases by 3.4%.

 

So, is what i am experiencing considered normal? (ie -20 equals a reduction in 13.6 percent)

And yes, i have lubed them

 

While they may be getting a bit weak, this is normal. Would wait until the Spring to replace unless you cannot deal with it as is. Sale is only on for a few more days in case you want to purchase for that day. New will be slightly better in this weather but will degrade, again, over time.