Just bought 99 XJ. Need maintenance info

I just bought a 99 Cherokee with 178K miles. It is in great condition! I want to replace all the fluids and do a tune up before I start modifyinng it. I need to know what kind of fluids to use. I read that the trans and tranfer case both use Mercon/Dexron 3. Is there a better fluid that I can put in it? Also, do you use what weight of gear oil do you use? I saw some folks saying they used 70w140 for offroading and towing loads. I would like to get synthetic fluids for the trans, transfer case, and diffs if possible. Mobil 1 and Royal Purple are readily available around here. What plugs do you recommend for my motor? I generally use whatever the factory put in on a stock application, but if there are plugs that give more performance or mileage, I'll get them. The Jeep has a fuel filter and 02 with around 10K miles on them, so I'm good to go there. If I am forgetting anything, let me know and I'll pick it up too.

I just found out that the O2 and fuel filter have not been changed. What is better Mopar or Bosch O2 sensor? Also, does the XJ have a fuel filter? If so where is it located?

Transmission (if it's an automatic) - Mercon/Dexron III (or IV...whatever they're up to now). STAY AWAY from the synthetic's...ESPECIALLY if it's an automatic transmission. Some on here run synthetic with no issues, but a lot of switched and ran into slipping issues. The AW4 Automatic can be real picky about what you put back in it.

Transfercase - Same as above

Front and Rear Differentials - 75W90 unless you do a lot of heavy towing, then I would probably bump it up to something higher. You can go synthetic if you wish on whatever weight you choose....i've been considering switching over myself here lately.

Coolant - your preference....i'm a fan of Peak Global myself

Spark Plugs - there's a lot of argument on this as well. A lot of people have tried Champion truck plugs and had problems, while alot of others have not.....most say stick with what's in it from the factory, which is another version of Champion if i'm not mistaken. Personally, i've got Bosch in mine (grew up using Bosch in all our vehicles) and it runs just as good as it possibly can.

Fuel Filter is inside the tank...so if you're going to drop the tank to replace that, you might as well go ahead and put a new fuel pump in while you're in there. No sense in dropping the tank twice.

Cool. Thanks for the heads up on the synthetic fluid in the tranny. I would have definately used synthethic and that would suck if I made my trans slip. I'm definately not going to drop the tank until it needs a fuel pump. I just was asking since I usually do a fuel filter as part of my new to me vehicle maintenance.

Run some Seafoam throught the brake booster vaccum line before the tune-up (several write on here about how to do it)
I run NGK plugs
brass cap and rotor button
belden NAPA plug wires
I would run syn in the diffs and transfer case. (Mobil 1, asmoil, royal purple it doesn't matter there all high quality)
regular dex/mer in the tranny
I would take off the throttle body (buy new tb gasket) and give it a good cleaning also take the IAC off and clean it. Use old toothbrush or small soft wire brush
Remove the EGR valve clean it out good. (If that year Jeep has one mine is an 1989)
Flush and refill the radiator
check and change u-joints (very cheap insurance)

Thanks for the replies. Does anyone have an opinion about the oxygen sensors? OE vs. Bosch vs. ??

I have had good luck with Bosch O2 sensor. I would buy them for my Jeep and I would say there cheaper too.

Do yourself a favor and get a Factory Service Manual. It has tons of info and repair procedures for everything.

Finally remember that JEEP stands for Just Empty Every Pocket.

-- Editted by Administrator.