Here lately I have seen a lot of threads and posts about preventative maintenance. Someone may have purchased a new-to-them XJ and wonder what they should check. I am still relatively new to this forum, but I have developed a passion for the XJ, and I want to contribute as much as I can. I am basing most of my thread of my experiences with my 96 4.0 XJ. You always need to do your research into your own year models to get the right parts or tools. I will try to not use any lingo or jargon to keep things simple to read for all levels of "mechanic". This is written around a 4.0 engine. I have not included anything to do with the manual transmissions.
So lets get started!
Oil Change -
So you just got your XJ and your performing the first oil change on it. "What brand, weight or filter do I use?"
Brand -
Brand of oil is totally up to you. Find what fits your budget. As long as the oil meets API standards, it should run just fine in your jeep. Name brands have different additive packages that can make them more "effective" at cleaning, preventing sludge and longevity amongst other things. There are forums out there that are dedicated to oil and have TONS of information available as far as oil analysis, ect... I personally choose Mobil1. I have been running Mobile1 for years now, and I have been happy with the results. There are several brands of "diesel" oils like Shells "Rotella" line, Mobil's "Delvac" or Chevrons "Delo". These oils have high zinc content that helps with preventing wear in our engines. These oils are also high in detergent to help clean and prevent sludge. Our engines have a flat tappet hydraulic lifter and cam, which benefits from the added zinc in the diesel oils. The downside to this extra zinc, is the damage that it can due to a catalytic converter. So it is a give and take relationship. Some high mileage variants of oils have a higher zinc content that their counterparts, so that is always an option. So really do your research, and pick a brand that fits in your budget, and makes you comfortable.
Weight -
Many people have many differing opinions on oil weights. You ask 10 people and you may get 8 different answers. Really it all boils down to this. Without getting into centistoke's, how polymers allow us to have multi-weight oils and the exact temperatures that the oil has to be at to have the effective rating displayed on the bottle... I will keep it simple.
10w30 - means that in the bottle, or at a "cold" viscosity, it has the viscosity of a 10 weight oil... and at operating temperature, it has the viscosity of a 30 weight oil...
A lower number is a thinner weight.
So on a cold start... the oil is thinner (10) to provide better flow for quick lubrication to prevent wear, but will behave as a (30) weight oil at operating temperature.
So all that being said..
"what weight should I run in my 4.0?"
I would stay safely between a 5 weight and a 40 weight. So 5w30, 5w40, 10w30, 10w40, 15w40 are all good choices and really depends on your climate for the one you choose! I would recommend getting a lower weight oil for cold winter climates (10w) for 20 to 50 degrees to be on the safe side and (5w) for anything below 20 degrees. I have no experience in "arctic cold" conditions, so there may be guys running even thinner weights for extreme colds. Of course these are just safe recommendations and there are jeepers out there probably running thicker weights or thinner weights year round with no issues. Once the summer heat comes, you can run a 10w or a 15w just fine.
10w30, 5w40(diesel oil) and 15w40(diesel oil) are very popular choices from my research on this forum. So if the zinc content is what you are looking for, running 5w40 in the winter time and 15w40 in the summer time would be a great choice! If you want to stay away from the zinc, then 10w30 is also a great all around choice for mild climates.
Filter -
This is also one of those things where asking 10 people will give you 8 answers. But one thing I can tell you that is unanimous, DO NOT RUN A FRAM FILTER. They are seriously HORRIBLE for your jeep.
Popular choices include WIX, Mobile1, Royal Purple, Napa Gold, Purolator, MOPAR, K&N, amongst others.
There are over-sized choices for all of these filters. Here is a list that I grabbed from another forum from a book titled
High Performed Cherokee XJ Builders Guide by Eric Zappe
These numbers are good for the 1991 to 2001 Cherokee 4.0
The first number is the stock filter size, the second is the over-sized
AC Delco PF13 PF2
Fram PH16 PH8A
K&N Gold HP-2004 HP-3001
Mobil1 M1-204 M1-301
Motorcraft FL332 FL1A
Napa Gold 1085 1515
Purolator L14670 L30001
WIX 51085 51515
The normal oil capacity is right at 6 quarts... but adding an over-sized filter could add around .5 quarts... so just take your time with filling and check to confirm proper oil level. And always check your oil with the vehicle turned off.. on level ground.. with the oil settled into the crankcase.
Interval – I usually recommend the average person change their oil every 3000 miles. There are synthetic oils that allow longer intervals between oil changes. But a good general rule of thumb is 3000 miles. There might be those that perform oil analysis on their jeeps, but this is getting beyond the typical person.
Transmission Fluid -
The AW4 automatic transmission takes dexronIII/mercon transmission fluid. IT DOES NOT TAKE ATF +4
The capacity is around 4 quarts with just draining the pan and refilling. If you drop the filter it’s going to take more to get it filled back up. If you picked up your jeep, and the transmission fluid looks/smells burned. It will take you a few drain and fills to get it back to looking red. My transmission took 4 drain and refills to finally look decent again.
As far as brands go, I like Valvoline. But any brand as long as it meets the dexronIII/mercon spec should be good to go. It’s your transmission, so you pick the brand you are comfortable with and fits your budget.
I like to drain my transmission every year and refill with fresh fluid. Its cheap insurance and it keeps your AW4 happy.
Front and Rear Differentials -
I grabbed this from another post on this forum from KD3NE
LUBRICANT SPECIFICATIONS
For normal vehicle operation, use SAE 75W-90, API Quality Grade GL-5 gear lubricant in all Jeep front (4WD only) and rear axles. Vehicles equipped with a Trac-Lok rear axle also require a friction modifier additive included with the gear lubricant.
When involved in trailer towing applications use SAE 80W-140, API Quality Grade GL-5 gear lubricant in the rear axle. XJ Vehicles equipped with a class III trailer hitch require SAE 75W- 140 synthetic gear lubricant in the rear axle.
You can use a gasket, rtv or both to seal up your diff covers. I like to use a gasket with a LIGHT coating of rtv just to help seal things up. Make sure to clean up as much of the old gear oil from inside the housing as you can.
For the average driver I usually recommend to drain and fill your differentials at least every 2 years under normal driving conditions. I usually add this into my yearly tune up along with the transmission, but at least every 2 years to keep things clean.
Fuel System –
1987 – 1996 Jeep Cherokee’s are equipped with an in-line serviceable fuel filter. Wix part number 33486. I really recommend once a year replacement on fuel filters. It is cheap insurance to keep your system clean.
There are several fuel system treatments on the market to add to the tank to keep moisture and ethanol problems out. I like BG44K, Seafoam, RedLine amongst others. Just occasionally add a bottle to the tank throughout the year and you should be fine!
Coolant –
Conventional Ethylene Glycol coolants were usually good for around 30,000 miles. The universal (all makes, all models) coolants on the market have a longer service life so I usually recommend running them. Our stock cooling systems are not exactly the greatest on the market. So I usually recommend every 2 years to flush and fill coolant depending on your driving habits. Keep it at a 50/50 mix for the average climate.
Brake Fluid –
Standard DOT3 brake fluid is fine for the Cherokee. During my Bi Annual checks I like to go to all 4 wheels and bleed some brake fluid out. This helps keep everything fresh and the fluid closest to the calipers and wheel cylinders gets the hottest. Start at the furthest wheel from the master cylinder and bleed toward the master cylinder.
Power Steering –
In my experience as a wrench turner, the two most neglected fluids of a vehicle are the brake fluid and power steering fluid. Basic power steering fluid is just fine for the Cherokee. I prefer Valvoline MaxLife, it has great reviews online and has worked well for me in the past. Every year it is a good general practice to suck the fluid out of the reservoir and add in fresh fluid. This keeps things fresh and will extend the life of your pump.
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With all the above information, what should you check, clean or replace when you first purchase your XJ? These are some good points to hit the common areas of failure that I see the most threads started on. This is by far NOT EVERYTHING you should check, but it’s a few good spots to work on. It is always a good idea to poke your noggin under your jeep and look around. Pop the hood and be aware of what’s going on under there. I can’t type out a write-up for everything I am listing, but using the search function should bring up a wealth of information.
1. Change ALL fluids and filters, who knows WHAT the previous owner put in there.
2. Full tune-up – Spark plugs (.035 gap), Wires (use Dielectric Grease on cap and plug boots), Distributor Cap (depends on year), Distributor rotor (depends on year), Ignition Coil, Crankcase breathers and grommets, serpentine belt (optional depending on condition), Air filter, fuel filter (see #1), o2 sensors
3. Grease all of your front end steering and suspension points.
Now you know all the fluids, filters, and tune up stuff is done.. what next?
1. Clean throttle body and the Idle Air Control Valve.
2. Back flush your heater core!
3. Upgrade your electrical grounds!
So many problems can be avoided by just doing the above mentioned 3!
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Leaks – So you popped your head under your jeep and it looks like an oil bath! Where do you start? The best place is from the top!
The valve cover – The valve cover leaks and drains down your engine and can look as though it is a rear main seal leaking. Always check around your valve cover gasket for fresh oil leaks. You might need to use an inspection mirror and a flashlight to get a good look at the rear of the valve cover. If you notice it leaking, then give it a good bath with some degreaser. I like to use Gunk degreaser; it has worked well for me. (Never directly pressure wash your engine unless you are aware of how to protect your vital electronics and sensors)
Oil filter adapter – The oil filter adapter o-rings will get hard over time and start to leak oil down the side of your engine. This will coat the starter and the oil pan. If you notice the side of your engine looks like an oily blob, then degrease and clean this area. Purchase the 3 o-ring set from your local dealership or online, and replace them! This adapter is notorious for being a huge pain the butt to remove. There are plenty of write-ups for the removal and replacement of this. Have a buddy helping you, and good luck!
So either these were not leaking, or they were leaking and now you cleaned them up. Whats next?
Clean the underside of the engine!
Cleaning all of this up will help you to narrow down the possibility of having to pull your engine oil pan and replacing the rear main seal. A lot of times it is not the rear main seal, but the above mentioned prone leak points. Narrow it down to make the best decision on whether you want to tackle the oil pan or not.
I hope this helps someone!