Home Forums Gear Hunting Trucks and Four-Wheel Drives Daughter's Jeep?

My Daughter bought a 88 Jeep Wrangler YJ for her first car with her own money a little over a year ago.






The 258 inline six is burning oil, we're to the point it's burning 5-6 quarts every oil change and we're doing a spark plug change every 3K miles as well. Engine has great compression in it 125-130 psi on all six cylinders. The engine is a rebuilt and I had sitting on a stand in my garage for a few years as a spare for my Jeep, that we swapped in after her original engine tested 50-60 psi on cylinders 5 and 6. Engine was properly broke in after install, but it has always used oil. This makes me think the rings were installed wrong or the valves never seated properly. She tried to get 6K miles out of the last set of plugs (L to R cylinders 6 to 1):




I converted it to PFI Systems TBI fuel injection shortly after she bought it, which made it a lot more reliable as far as starting and running. She wants to keep the Jeep which I understand as I have an 84 CJ7 that I love, and she has another vehicle to drive that's very reliable and she can take it with her when she graduates HS in the spring. She's 17 currently and a pretty good driver, but she's 17.

So I'm looking at options for the engine, and here is what I come up with.

1. Rebuild her 258 ci engine that's currently on my stand or order a rebuilt long block. $2500

2. Find a 4.0L core and drop a rebuilt/reman 4.0L running the current intake with TBI fuel injection. $3000

3. Find donor Jeep with a 4.0L and AX15 transmission, upgrading her to MPFI and a stronger transmission to eventually run bigger tires. I have a line on a running 99 XJ Cherokee with 150K on it but hit hard in the rear quarter for $1500 obo. I'm guessing $5-6K total if I decide to go through the engine and transmission before swapping with over runs on things.

4. Install a 4.3l V6 and AX15 transmission, this will set her up for a future LS motor swap and bigger tires. I just don't think shes ready for a 300 HP V8, that'll drop 100+/- lbs of weight total on the vehicle. So that's my reasoning for not going with a 5.3 or 4.8L motor right now.

I’m no Jeep expert, but I had a buddy that was the sales manager of the largest car dealership in town and I asked him once what engines they saw that seemed to last the longest. He said that they see the most miles on the 4.0 Jeep, 4.6 Northstar, 3.0 Ford and 3.8 Buick. That was a while back, but given that, I’d opt for that 4.0 in your daughter’s Jeep if you can find one.

Those 4.0 straight 6 engines will run forever, so your's seems to be the exception to the norm.

If you have the skill and time, I'd suggest rebuilding the current engine. There has to be something seriously wrong with the engine if it is burning that much oil and fouling plugs like that. I had a 1990 Cherokee Limited and a 1994 Grand Cherokee Laredo with the 4.0 straight 6. Both engines ran over 100,000 miles without buring any oil, always have used full synthetic in them, but the value cover gaskets and the oil cooler lines always seemed to seep oil.

My 1983 has a 4.0 in line injected 6, 5 speed, i have replaced the clutch once and tires when needed it has just over 300,000 ranch miles on it, my 2005 LJ in line 6 has 175.000 ranch miles replace clutch and rebuilt the front end, tires, no engine repair on either Jeep just regular service. the in line 6 is damn near bullet proof. Rebuild the 4.0 Rio7

She doesn't have a 4.0L engine.

The engine in her Jeep is the older 4.2L or 258ci engine. The engine either sat too long without being used or the rebuild was bad. I could probably rebuild the motor, just lack the proper tools and more importantly time to do it in my garage.



Must be a 1993, unless someone did a swap? 1983 would make it a CJ Jeep. The 4.0L common rail Jeep motors didnt exist untill 1988 in the XJ Cherokee and 90 or 91 in the YJ Wrangler. Also anything after 92 would be the 4.0L H.O. motor.

I didn't realize that Jeep used a straight 6 other than the 4.0. I had a 1986 Cherokee with a 2.8 V-6 that was a bad motor. I got it from an USAF guy who was transferred while deployed to Iraq in 1990. He left the title with his buddy and I bought it for $500, a steal even with the crappy motor. I drove it for awhile and then sold it to a local girl as a school car for what I had in it.

I've had both the 258 and the 4.0L. Give me the EFI 4.0L if I have the choice. It is still a great little motor.

Valve stem seals?

Basically the same block, different bore, stroke, and a much improved head. The head along with common rail multi port fuel injection probably made the biggest improvements to longevity of the motor.

Sorry my old Jeep is a 1993 not a 1983, 4.0, my mistake. Rio7

check the valve stem seals. if they are the cup type they will get brittle if a motor sits for a time . a puff of white smoke when you first crank it ?

Just order a long block and install. You will be good for a long time. Plus you know it is new.

Oil fouled plugs? Does your coolant look good?

Coolant is fine, no issues there.

Such a fine looking machine in that picture, and your daughters first car, I hope it's something simple and quickly made right.

It's simply money!

The issue is either in the top end or the bottom, and I can either take it in and diagnose the issue and rebuild again; or I can just start over with a different long block. If it is in the bottom end of the motor, I can't rebuild unless I'm willing to sleeve the cylinders if it needs to be bored out. A new head is pretty affordable but again I'm afraid it will be the diagnosis that'll eat the money.

Its one of two things, valve seals, or the rings were installed wrong, the valve seals are a simple fix that you can do in a couple of hours, if that's not it, I would say the rings were installed with the gaps aligned or the wrong oil rings.

Just rebuild the engine. The 4.0 engine is pretty bulletproof and give decent power. As long as you don't go crazy with lifts and tire she'll be fine. As an older and shorter man, I wish I stuck with a two inch lift and 31 inch tires to make it easier to get into.

If you buy new, an LS swap would be pretty cool. And not to much difference in money. But this would lead you down the rabbit hole of better transmission (AX15 would work with V8 but better choices out there), lift, tires, ect.

Pretty sure the 88 model she has is a 4.2L (258ci). The 4.0L came around 1991 or so.

And I hear you on the lifts. A 32-33" setup is great for still being drivable on the highway.

I really don't want to do an LS swap, but that's the only answer that I'm getting on a Jeep forum. They just say it's pretty much the same work as wiring in the MPFI 4.0L as an LS motor. An AX15 is just a pretty easy transmission to source and fits really well in the Wrangler.