If the is struggling to start when cold, there are two possible reasons.
Reasons for car struggling to start when cold
(1) Use of heavy single weight engine oil.
(2) Weak battery.
Car troubleshooting
If you are using heavy single oil, then the problem is too thick engine oil. As indicated, the car is using a heavy, single weight engine oil. This type of oil tends to become very thick in cold temperatures. In fact, it can become so thick that the engine has trouble cranking when you try to start it because of the extreme friction caused by such thick oil.What to do?
Change your engine oil to a multi-weight oil such as 10W-40. This type of oil will not thicken in colder temperatures and thus not cause hard starting when the engine is very cold.
If you are not using heavy single oil, then the problem is the weak battery weak. Cold outside temperatures can cause a battery to become temporarily very weak. A weak battery will of course not be able to crank an engine fast enough to start it.
What to do?
You should replace this battery with one that has a good "Cold Cranking Rating" - this is a battery's ability to work in very cold temperatures. Visit your local auto parts store and ask the salesman to recommend such a battery. Get the best battery you can afford - it will be money well spent.