4.0L Oil Filter Adapter

Changing a 4.0L Oil Filter Adapter

There's a leak from your engine, somewhere on the right side. You can't find the source, but it's coating the rear of the engine, along with the bellhousing, starter, exhaust and transmission.

The leak is often from the oil filter adapter - a bolted-in casting that connects the oil filter to the engine block. On early 4.0L "Renix" engines, this adapter held a metrically-threaded 1/2-qt filter vertically upside-down. When this filter is removed, oil commonly drains out onto the block, starter and axle.

On later 4.0L "High Output" models, the oil filter adapter holds an SAE-threaded 1/2-qt filter horizontally. This allows you to remove the filter without losing as much oil, and also uses a more common 3/4"-16 threaded filter. However, as I note at the bottom of the page, you can add another half-quart oil capacity and gain a larger filtered area by swapping in a 1-quart filter. But I digress...

There are two o-rings on the bolt, and a third (removed already) on the adapter
The adapter and holddown bolt shown above, with the o-ring package.

The Jeep dealer should have a set of three o-rings for your vehicle; if there's not a Jeep dealer nearby, don't fret. Dodge and Chrysler dealers use the same ordering system. Total cost was somewhere around $8 when I ordered mine awhile back.

Whatever engineering group designed the layout of the 4.0L engine in the Cherokee should be forced to turn wrenches in the dealership for a year because there's no way you're going to easily remove the T-60 Torx holding the adapter in place. The framerail sits about an inch away, and most socket-and-adapter combos are taller than that. I learned recently that some early versions of the 4.0L have a 5/8" hex fitting on the end of the adapter...no need to use a Torx adapter. One report from a Canadian 1991 Grand Cherokee 4.0L owner stated that his adapter was held in place with a 9/16" hex key.

Hopefully it goes without saying that you should really only do this in the middle of doing an oil change if possible...otherwise expect a considerable amount of oil to spread down your arm and driveway.

Remove the oil pressure sender connector and tuck it safely out of the way. This should be done with every oil change anyway, because you don't want to accidentally crack the housing and end up burning up your rig.

Wipe off the area around the oil filter adapter; you've probably got a bit of grime there anyway because of the oil leak and you don't need to get the engine guts dirty unnecessarily.

If you haven't already, remove the oil filter.

Gettin' Dirty

However you actually do remove it, the oil filter adapter is going to be in a tight place. Readers with Wranglers are going to have a little more room to work with, but in my Cherokee I had only about an inch or two available to fit the T-60 in there before it hit the framerail. There wasn't enough space for the entire T-60 in the 1/2" drive socket housing, so I used a punch to drive the T-60 out.

**Warning** The bolt holding the adapter in place will be TIGHT. Plan your wrenching so that when your wrench slips it will not hit fragile underhood components such as the oil pressure sender or your fingers.

Rumor has it that if you have the earlier metric-threaded 4.0L Renix engine that you can convert it to the later model simply by swapping the adapter to the later model. If I can verify this with certainty I'll edit this section. Until then, the metric adapter holds the filter upright, above the filter. The SAE adapter points the filter back along the engine.

Buried somewhere under that mess of wires and hoses is the aluminum oil filter adapter
This is a mockup of the wrench configuration I used to remove the bolt
This is a mockup of the wrench configuration I used

I used a pair of 12mm combo wrenches to hold the T-60 in place; they were approximately 180* opposite each other so I could rotate the T-60 without pushing it too far sideways. Once the bolt finally loosens and you can remove it, the adapter will start to spin as well. Take care not to damage the pressure bypass, that's the small tube extending out of the block near the top of the adapter.

To remove the Torx bit itself, I tapped the back of the bit with a punch while it was resting on a deep socket that gave me room to remove the bit.

Carefully pull the bolt and adapter out, and clean them off. The picture shown earlier is my "after" shot, because before doing this, the entire passenger side of the engine was grimy black. Now, even more than a month after changing the o-rings it's still very clean on that side and I have no mystery leaks from the engine.

Filter removed, note the oil pressure bypass
The adapter has been removed. Note the oil pressure bypass

Soak the o-rings in a small dish of motor oil before putting them on the holddown bolt; they are three different sizes so unless you weren't watching when you pulled it out you can reseat them rather quickly.

Reinstall the adapter and bolt, and tighten down to 75 ft. lbs of torque.

Lube the sealing ring on the oil filter, and reinstall. Fill with 5.5 to 6 quarts of your favorite oil, and drive. Enjoy.

Application Wix Filter Dimensions Filter Thread Other Brands

4.0L I6 1987-90

2.5L I4 1987-90

2.1L I4 Renault Turbo-Diesel 1985-87

51626 3.8" high
3.663" diameter

Purolator PER4670

Fram PH3985

AC-Delco PF9

4.0L I6 1991- (2006?)

2.5L I4 1991- ?

51085 3.790" high
3.660" diameter


Larger capacity substitute for 1991+ motors 51515 5.178" high
3.660" diameter

AC-Delco PF2

Fram PH-8A

Motorcraft FL-1A

Mobil1 M301

Purolator PER1A

All of the above filters have the same size gasket mating them to the oil filter adapter on the engine block; 2.834 OD, 2.462 ID, 0.200 thick

As with all technical information, especially with Jeeps, do not blindly trust the info given in any manual or website until you verify it with your own eyes. Jeep is notorious for building 99.8% of the vehicles in any given model year to one spec but they seem to use random parts found in a warehouse on the other 0.02%...

e-mail Jim
created: October 31, 2005
Updated August 17, 2006

All content is copyright 2001-2006, and unless otherwise noted content comes solely from the mind and keyboard of Jim "Yucca-Man" Langdon
Any changes or modifications to your vehicle are at your own discretion; I take no responsibility for your lack of responsibility