Scheduled Maintenance Interval

I'm new to this forum and not a car expert, but I enjoy my car the same as all you, senior members.
I bought my last Century in 1990 and at that time the official maintenance interval was 3000 miles for oil changes and 1 year for antifreeze, in hard driving conditions. Now 12 years later with the Century that I purchased Saturday, the intervals are a lot longer.
My Question, what is the realistic interval for oil, antifreeze, and spark plug changes? Thank you in advance.

dear buick century owner...

automotive mfgs. (to sell more cars) greatly reduce the scheduled maintenance programs that are factory reccomended... this is so that
they are able to put a lower dollar figure on the window sticker in the box that denotes anual average of scheduled maintenance... my recomendation is that you visit a local auto service facility, some type of reputable place... like a goodyear, firestone, michelin dealer or chain store... they will most likely have some type of literature on the subject on what they reccomend .. not what the mfg reccomends... and by the way the worst thing that you can do is not change your coolant regularly. GM installs orange coolant now.. this is called dexcool. it breaks down faster than standard glycol (green stuff) change it every 30k.. or you will most likely develop coolant leakage problems...

hope i was of service

I recommend you look in your owners manual for recommended service. Most dealerships that I know of follow the short trip intervals and not the highway ones. Most of the newer cars dont really need a whole lot on maintenance like the old ones did although keeping them at optimium performance is the key to longevity. Myself I do oil changes every 2500 to 5000 depending on where I've been and how I've been driving. Coolant, every 12 for green and every 50 for Dexcool, the key to Dexcool is keeping your system full of the correct percentage of mixture. Trans fluid every 30000. Again your owners manual will give you the correct advice.