Go with the service intervals in your owner's manual, unless you drive like a little old lady only on sunny sundays, I'd consider using the "Sever Duty" schedule instead of the "Normal" schedule. Put some thought into it, they describe what makes a sever duty condition, and if you really do NOT meet it, and following the sever schedule is too hard or expensive, you might want to go to the normal or somewhere inbetween for a few items like that.
If you do NOT have service records from the prevous owner, assume only oil was changed, that is all most American Vehicle owners do for servicing their vehicles. So, anything in the service schedule in the owner's manual, that is NOT changing oil, I'd assume was NOT done and the vehicle is overdue.
The modern ignition systems do all sorts of things different from the old systems, NOT just any plug will do anymore. You will see lots of people complaining about switching to a different kind of plug and having ignition problems. I'd just play it safe and replace the plugs with the exact brand/model recommended in the owners manual.
Some of the Jeep Commander's engine have ignition systems that use reverse current on half the plugs, and if you use a single platinum plug with that kind of ignition, half your plugs will be worn out in no time, if you're going to go platinum, go double platinum if your engine has that type of ignition.
Besides, weak ignition costs you power, but after the ingition is strong enough, more ignition energy does NOT get you any more power or economy. Most of the claims plug manufacturers make are bogus, 99.99999% of the time you will NOT get extra power because you switched to a different spark plug. Of course, if your plugs are worn out, you will get back a couple of HP you lost from worn out plugs, so you may notice a little pep from fresh spark plugs, it is just the old pep your motor always had, that you didn't notice degrade slowly over time with the plugs wearing out.
Make sure you have the right fluid, NOT just any fluid that is for Power Steering, for transmissions or axle lube, etc... There is specific recommended fluid you are suppose to use and it will make a difference, again, Owner's Manual will tell you what to use.
Axle Fluid, a lot of the Commander's Owner's Manauls say "If you use the vehicle for Taxi, Fleet or Police use, Tow or Off Road" change the axle fluid every 15k (some 18k) miles. Usually says to use 75W-140 Synthetic Axle Fluid. If you don't meet the Taxi, Fleet, Police, Tow or Off Road, you don't have to change the fluid at all. Towing and Heavy Loads does cook the fluid, so if you are doing a lot of towing or Off Roading, yea, I'd change the fluid that often. I do that stuff only lightly and rarely, if at all, and changing axle fluid every 15k miles is too often for my tastes, as well never changing it is too little IMO also. So, on my own judgement, I change the axle fluid every 30k miles. Of course, if I ever do any real heavy towing or tow often, or do some serous off-roading, like submerge axles in water, I'd go back to the 18k mile change. But, towing an compact car 25 miles or driving over some grass every once in a while, or NOT doing any of that at all, I think I'll be OK waiting to 30k miles to change the fluid.
The Serpentine Belt, my 2010 Owner's Manual says replace at 100k miles. It can't hurt to replace early if you want, as long as you buy a quality replacement and NOT garbage. At least check the belt condition, look for dry rot, cracking, cunking, glazing, if the belt looks good, you can wait until the owner's manual says to change it.
Last edited by Mongo; 12-12-2011 at 10:45 AM.