Maintenance suggestions for 1998 4.0

[Christoph]

Purchased a 98' 4.0L. She runs fine and there aren't any apparent major issues, but I would like to give a good run through of maintenance and was wondering what that should consist of.

Currently has 166k miles and a small oil leak that I've read isn't entirely uncommon. Any guidance would be appreciated.

 

[CodaMan]

First thing to always do is change all the fluids (oil, transmission, transfer case, both differentials, brake) and do a coolant flush. Then you'll have a good baseline for all future preventative maintenance.

 

[Kid Mechanic]

Any guidance would be appreciated.

Kind of an open-ended question. Starting with @CodaMan’s suggestion. From there you can go mild to wild!
You could replace u-joints all around, axle seals, wheel bearings. Or wait until those items cause problems.

A few maintenance items to add to @CodaMan’ list would be accessory belts, brake pads, brake rotors. How are the tires?

 

[qslim]

As weird as it sounds O2 sensors are almost a maintenance item on these things. When I got mine it was running a tad off, not bad, but it would stumble here & there and it also sounded like it had an exhaust leak. I did plugs/wires/cap, didn't really change much. I didn't even think about the O2 sensors because the CEL wasn't on, but after doing some reading on here I decided to try changing them with the recommended brand. That completely cleared up every little issue to include the ticking, runs perfectly now.

 

[Chris]

Overhaul the cooling system:
Jeep Wrangler TJ Cooling System Overhaul FAQ

Replace the spark plugs:
What are the best spark plugs for my Jeep Wrangler TJ 4.0?

Replace the O2 sensors:
The Official Jeep Wrangler TJ Oxygen (O2) Sensor Thread

Change all fluids:
Wrangler TJ Fluid Capacities

 

[Christoph]

Kind of an open-ended question. Starting with @CodaMan’s suggestion. From there you can go mild to wild!
You could replace u-joints all around, axle seals, wheel bearings. Or wait until those items cause problems.

A few maintenance items to add to @CodaMan’ list would be accessory belts, brake pads, brake rotors. How are the tires?

Got brand new tires and rims from Discount Tire today actually.

 

[Christoph]

Overhaul the cooling system:
Jeep Wrangler TJ Cooling System Overhaul FAQ

Replace the spark plugs:
What are the best spark plugs for my Jeep Wrangler TJ 4.0?

Replace the O2 sensors:
The Official Jeep Wrangler TJ Oxygen (O2) Sensor Thread

Change all fluids:
Wrangler TJ Fluid Capacities

You're the man. Looks like I've got a few thousand more to spend now though. lol.

 

[Chris]

You're the man. Looks like I've got a few thousand more to spend now though. lol.

It never ends

 

[Christoph]

It never ends

Truth.

Amazon says that radiator doesn't fit my 98' 4.0L Auto. Do you know where else I can find a Mopar one? Been googling for 20 minutes and can't find it. https://www.amazon.com/dp/B0049ELCF0/?tag=wranglerorg-20

 

[Chris]

Truth.

Amazon says that radiator doesn't fit my 98' 4.0L Auto. Do you know where else I can find a Mopar one? Been googling for 20 minutes and can't find it. https://www.amazon.com/dp/B0049ELCF0/?tag=wranglerorg-20

This one will fit your 98 4.0 auto:

https://www.amazon.com/dp/B0049ELCF0/?tag=wranglerorg-20

Amazon will say it won't, but it will. The only difference to my knowledge is the little fittings for the transmission cooler lines at the bottom of the radiator, but those can easily be swapped out.

 

[Christoph]

This one will fit your 98 4.0 auto:

https://www.amazon.com/dp/B0049ELCF0/?tag=wranglerorg-20

Amazon will say it won't, but it will. The only difference to my knowledge is the little fittings for the transmission cooler lines at the bottom of the radiator, but those can easily be swapped out.

Awesome. Thanks again.

Almost on the fence now of just flushing it and waiting for everything to poop out. Eventually going to do an engine swap and will have to get a new radiator again then. Not sure how much I should replace vs quick fix with 166k miles.

 

[Chris]

Awesome. Thanks again.

Almost on the fence now of just flushing it and waiting for everything to poop out. Eventually going to do an engine swap and will have to get a new radiator again then. Not sure how much I should replace vs quick fix with 166k miles.

If you live somewhere warm, the cooling system is always a nice thing to have in tip-top shape

 

[glowell222]

When you do the coolant system, be sure to back-flush the heater core.

I suggest a few spare parts, as well: distributor sensor (aka camshaft position sensor, though if you search using those terms you will not be happy), crankshaft position sensor, blower motor resistor. The '98s are at that age that these are definitely on the radar. Be sure to get the Mopar versions of these. Eventually the clockspring is on there as well, but they are not inexpensive and you can drive without it for a bit. For some reason, the oil fill caps are also an annoying item with that stupid ratcheting action.