Filtration for Jeep 4.2L, 4.0L and Inline Six Stroker Motors
The 4.0L swap
into an earlier Jeep CJ or YJ Wrangler 2.5L four or 4.2L inline six chassis has become popular. So is the stroker
build-up that uses the 4.0L inline six engine block.
Jeep 4.0L and stroker inline six buildups have become popular. 4.0L
conversions into the earlier four-cylinder and 232-258-4.2L six-cylinder Jeep CJ and YJ chassis are also
common. Whether you retrofit a stock 4.0L or build a stroker inline six, you will be using a 4.0L cylinder
block and head.
Oil filtration and the oil filter bypass system are concerns when
installing a 1987-up inline six-cylinder block into a Jeep CJ or pre-'87 full-size J-truck chassis. This also
applies to the stroker inline six retrofits, which use a 1987-2006* 4.0L Jeep inline six "long block"
*Note: When selecting a 4.0L long block core
or complete engine, I recommend use of a 1991-up engine for its improved cylinder head and other upgrades. The 4.0L
inline six was available in the Jeep XJ Cherokee, Jeep YJ Wrangler, Jeep TJ Wrangler and the Jeep ZJ and WJ Grand
long block is a 1991-up 4.0L design (specifically a mid-'90s application). This engine
is being retrofitted into a 1987 YJ Wrangler originally equipped with the 2.5L inline four. Note downward
facing oil filter like the 1987-90 4.2L inline-six engine. This profile would be identical for a
stroker 4.5L, 4.6L or 4.7L buildup.
Filter and By-Pass
The 4.2L and 4.0L inline Jeep sixes built from 1987-up use a
different oiling scheme than pre-1987 232 and 258/4.2L sixes. Oil filter types differ between
AMC/Jeep used two distinctly different oil filtration and bypass
approaches. View these engines as 1) those with in-block bypass valves like the 232 and
258/4.2L inline sixes built through 1986 and 2) engines that do not have a bypass valve in the block
built from 1987-up. The latter group includes the 1987-90 4.2L blocks and all 4.0L engine blocks
Note: The engine block passageways on 4.0L engines do not have a provision for a
bypass check valve. These engines all require an oil filter with the built-in bypass valve. The 4.0L engines
use an oil filter connector that must match the filter thread type and filter mounting
The bypass valve plays a critical part in
full-pressure oiling systems. In a full-flow system, the oil moves from the oil pump directly through the oil
filter, then to the lubricated engine parts. This provides optimal protection for the
If the oil filter becomes clogged
or flow resistance at the oil filter is too great, the bypass valve opens and allows oil to flow
directly into the oiling passageways—without being filtered first!
Caution: The intent of the bypass valve is to protect an engine with a clogged filter or
excess resistance in the filtration system. However, bypass oil is not filtered and can harm internally lubricated
parts. This is one more reason to change the oil and oil filter on a regular
This is the
bypass mechanism on a 1987 2.5L Jeep four cylinder engine...Pre-1987 4.2L inline sixes use a similar bypass valve.
This is an in-block bypass method. Over the years, several connector sizes were
filters on 232 and 258/4.2L inline sixes built through 1986 do not contain a built-in bypass valve. These filters
angle downward, similar to this 1987 2.5L Jeep YJ Wrangler four-cylinder application.
If the oil filter clogs on a pre-1987 AMC-Jeep inline six, the in-block,
spring loaded bypass valve will redirect oil flow. The oil "bypasses" into a passageway in the engine
1987-up 4.2L and all 4.0L inline AMC/Jeep sixes have the bypass mechanism
built into the oil filter. This is a common, modern method of filtering; the correct filter contains the
angled 1987-90 4.2L oil filter has a built-in bypass valve. The filter attaches directly to a 4.2L
engine block. Jeep CJ-era 232 or 258/4.2L inline six filters mount the same way. This filter, however, has
metric 20mm X 1.5mm threads and a connector unique to 1987-90 4.2L inline six engines. The CJ-era filters are U.S.
The 1987-up block design does not have an in-block bypass
system. Oil pump flow goes directly into the oil filter, flows through the (unclogged) filter, then
enters the engine's lubrication passages as filtered oil. When a clogged oil filter "bypasses", the
unfiltered oil flows from the oil pump directly into the engine's oil galleries.
Important caution: The "emergency" oil bypass system
protects the full-flow lubrication system from oil starvation. Whether in-the-block or in-the-filter, the bypass is
a last gasp response for the poorly maintained engine. Bypassing oil, uncleaned of impurities, will contaminate
bearings and cause premature parts failure. This is the reason for periodic fresh oil and
oil filter changes!
This article offers several Mopar PDF parts
illustrations with schematics for 4.2L and 4.0L engine bypass methods and filtration designs. Click on
the links for various engine applications, open the PDF and "zoom in" for details. Here is a
Jeep CJ 258-4.2L used through 1986 has an in-block oil
by-pass system with a spring, valve and retainer. The OEM Mopar J3242397 filter mounts directly to the
block. This filter does not contain a bypass valve. It has a U.S. thread with a 13/16"-16 pitch connector.
The filter unit offers no bypass protection and relies upon the bypass valve on the
you install a stock 4.0L or a stroker 4.0L block into a CJ chassis, the easiest approach is a 4.0L oil
filter with an in-filter bypass valve. Look closely at the 4.0L block—there’s no place for the earlier 4.2L bypass spring, valve and
retainer to fit in this block! Use the correct oil filter and filter
in many ways to the 4.2L block, the 4.0L uses an in-the-filter bypass valve, which relies on an oil filter with
anti-drainback and bypass valving built into the filter. (The 4.0L block passageways will not accommodate an
in-the-block bypass setup.) There are different oil filter part numbers for Jeep CJs versus YJ Wrangler
applications. Oil filter connector part numbers are also different; connectors vary in length and thread size/pitch
(including U.S. versus metric threads).
Warning: Some 4.0L oil filter adapter stands
have a filter connector with a built-in check valve. This helps prevent oil drainback from the upside-down oil
filter mounting position. If the adapter stand uses this type connector, keep it to prevent oil drainback and dry
filter start-ups! Use the oil filter listed for this engine
Note: As required by
your Jeep model's chassis and motor mount layout, use either a direct-to-block oil filter mounting method or the
horizontally mounted filter adapter. Avoid the straight upside-down oil filter adapter
unless upside-down is the only fitment
2) YJ Wrangler 4.2L built from 1987-90, the
filter still mounts to the block, but note that the by-pass is now an integral part of the oil filter. The filter
connector and oil filter are different than the CJ 4.2L type. The YJ Wrangler 4.2L does not use the in-block bypass
spring, valve and retainer.
This is a 1987-90 style YJ Wrangler oil
filter installed on a 4.0L engine block. In 1987, the 4.2L inline six abandons the in-block bypass valve and opts
for an oil filter with built-in bypass valve. The metric
thread 05012968AA filter shown (same fit as the Mopar #33004195) has a
built-in bypass valve.
3) 1991-93 4.0L YJ Wrangler—When looking at the part numbers in
the schematic, note that “MJXJ” is the Cherokee and Comanche pickup. “YJ” is the Wrangler. The YJ Wrangler gets the 4.0L in 1991. Bypass valving
is in the oil filter, not in the block.
Note: In the 1991-93 parts catalog's
picture, the generic illustration can be confusing. It shows a 4.0L XJ/MJ and ZJ style aluminum adapter
stand. In other references, the YJ Wrangler 4.0L does not use the stand-off adapter until 1994. (See
parts #18 through #20A, distinguishing YJ from XJ/MJ and ZJ.) When working with a 1991-93 YJ Wrangler
4.0L engine or core, confirm the filter mounting method. Use the correct filter connector and oil
4) The XJ
Cherokee and MJ Comanche pickup truck introduced the 4.0L inline six in 1987. These engines use a stand-off
filter adapter. (Oil filters on the Jeep MJ, XJ, ZJ or WJ models do not mount against the block.)
1987-90 MJ and XJ 4.0L oil filters have 20mm X 1.5mm metric threads. 1991-2006 4.0L inline sixes use a U.S.
thread oil filter.
5) 1994-up Jeep YJ Wrangler oil filtration joins other
4.0L applications with a stand-off filter adapter; on stand-off adapters, note whether the filter mounts
horizontally or upright (upside-down). The adapter stand indexes on a locating pin in the engine
block; the position is clear.
Mopar 05281090 oil filter is common
on 1991-2006 Jeep 4.0L inline sixes. This quality filter handles a stroker motor's needs, too. The filter has
built-in bypass valving.
Note: From 1997-2006, the Wrangler is a “TJ”. “ZJ” and “WJ” are the
Grand Cherokee models.
6) On any of the
stand-off oil filter adapters, install new O-ring seals on the mounting bolt to the block. Make sure you tighten
the mounting bolt securely*. Get the Mopar seal kit for your 4.0L engine or core application and adapter
design. Verify kit and O-ring part
numbers for your 4.0L block application.
When working with a stock 4.0L or a stroker
motor, always replace the O-rings on the adapter bolt. At mileage, Jeep 4.0L inline sixes will develop leaks
at these O-rings.
Listed "factory" torque figures for the adapter bolt are all over the board. Some call for 50 ft-lbs, others
indicate 75 ft-lbs.
These bolts are always very tight coming off. Secure tightly enough to hold the stand and a filter in place while providing a leak-proof seal at the O-ring. At
mileage, this is a common leak point for the 4.0L engine, easily remedied with an O-ring seal
Jeep owners who acquire a 4.0L block with a stand-off oil filter mount, this filter position may not work with the
pre-1987 Jeep CJ motor mounts. Even as an OEM approach on later Jeep models, this mounting position is not
convenient for oil changes. A spillage mess can occur during routine
Right Filter and Filter Adapter
CJ retrofit installations should consider mounting the
filter to the engine block, preferably with a U.S. thread oil filter. The 1987-up 4.2L and 4.0L
oil filters provide built-in bypass valving and can mount directly to the block with the correct
connector. (You will remove the adapter locating pin if you eliminate the adapter and fit the filter to the
This mounting method looks much like a CJ 258/4.2L or 1987-90 YJ 4.2L
approach. The filter points downward; however, you must use an oil filter with internal bypass
Note: The common 4.0L Wrangler oil filter
connector is Chrysler/Mopar part number 53007563. The filter is the popular
1991-up 4.0L Mopar 05281090. This filter is U.S. 3/4"-16 thread.
Pre-1987 AMC/Jeep inline sixes have the in-block bypass valve. They also use a 13/16"-16 U.S. thread oil filter
connector fitting. The oil filter or connector for these earlier
258/4.2L sixes should not be installed on a 1987-up Jeep inline six block—there is no bypass valve in the
1987-90 4.0L and 4.2L engines each use the same oil
filter (the Mopar 33004195 or equivalent). These blocks do not have an in-block bypass valve*. This
filter fits on 20mm X 1.5mm threads. The filter has a built-in bypass
*Caution: The 1987-90 4.0L Jeep inline
sixes use an upright (upside down) oil filter layout. The metric connector accepts the 33004195 oil
filter with built-in bypass valve. This is a briefly used oil filter adapter that requires the 1987-90 metric
oil filter connector with 20mm X 1.5mm metric oil filter threads.
If your Jeep is a 1991-up model, the oil filter goes back
to U.S. thread type. 1991-up 4.0L engines use the Mopar 05281090 oil filter or equivalent. This filter has a
built-in bypass valve. Thread size is 3/4-inch, 16 threads per inch.
Many 4.0L conversion engines and stroker motor cores come
from the 1991-up XJ Cherokee or a ZJ/WJ Grand Cherokee 4.0L six cylinder model. These engines use the
stand-off filter adapter and the common U.S. thread Mopar 05281090 oil filter mounted either upright
(upside-down) or horizontally on the adapter stand.
Caution: If you install a
4.0L or a stroker derivative inline six into a pre-1987 Jeep, make sure the oil filter has a built-in
bypass valve with the correctly threaded connector!
inline six engine block does not have a provision for an in-block bypass valve system. Here, the needed height
for the oil filter connector is determined with a depth gauge. This block is the same as a "stroker six" core and
requires an oil filter with built-in bypass valve. The installation is a retrofit into a 1987 Jeep YJ
Reminder for CJ and 1987-90 YJ Wrangler
owners: Oil filter
connector threads must stand out far enough for the filter to mount safely...The YJ Wrangler 4.2L six uses
the Mopar 33003538 oil filter connector and metric oil filter with built-in bypass. If you use this approach,
make sure the connector seats properly at the block and provides enough filter-end thread
exposure to safely mount the #33004195 metric oil filter. If you prefer using the U.S.-thread 1991-up YJ
Wrangler oil filter connector (Mopar #53007563), this will
mount the filter directly to the block like the YJ Wrangler 4.2L application. The 53007563 connector has
U.S. threads and takes the 05281090 Mopar oil
On this 4.0L (or stroker six) engine block, the oil
filter connector did not stand out far enough. A pre-1987 bypass valve retainer has been modified to act
as a spacer. The older (pre-1991) connector will accept the 1987-90 #33004195 metric oil filter with built-in bypass
This Mopar Remanufactured 4.0L inline six comes
with a spring roll pin for positioning an oil filter adapter stand. (If the engine uses an oil
filter adapter stand, a pin must be installed.) At right is a spacer fabricated from an earlier Jeep
engine's bypass retainer that will index on this roll pin. Making a spacer is not
necessary if you find the correct connector for the
Caution: Any time you install a connector fitting, make sure it will seat squarely and securely at
the engine block or adapter stand. Also be certain that there is enough thread exposure for the oil filter to
attach securely. Torque parts properly; you don't want the oil filter to come
The older style metric connector fits
through the retainer. Modified retainer acts as a spacer and uses the 4.0L adapter locating
pin to keep the assembly from rotating. Red Loctite 271 on block-to-connector threads is added
insurance. Apply Loctite to connector threads only; keep Loctite away from the oil
Note: Use of a spacer is
only necessary if you cannot find the right connector for the oil filter. See the factory parts schematic
PDFs for details. Avoid parts fabricating unless you must for your
of the locating pin, fabricated spacer/retainer and a 1987-90 oil filter connector is shown here. Oil
filter has built-in bypass valve, required for a 4.0L or stroker engine block. There is no bypass valve provision
in the 4.0L or "stroker" block.
Note: Use of the 1991-up 4.0L oil filter
connector (Mopar #53007563) should eliminate the need
for custom fabricating a spacer as shown in the hybrid approach (above). Do not use a spacer unless
If your Jeep
model's engine bay and motor mounts require use of a stand-off filter adapter, apply the 1991-up mounting method if
possible. This provides the more common U.S.-thread filter and connector option. Shown is a
'99 XJ Cherokee 4.0L that takes the 05281090 Mopar oil filter. The filter mounts horizontally on the adapter
When seeking a 4.0L inline six engine core,
the 1991-up engines are preferred. They offer an improved cylinder head design and other upgrades. If possible, get
the OEM 4.0L oil filter stand and hardware with your 4.0L engine core. If this does not fit your Jeep Wrangler or
earlier CJ chassis properly, consider the alternatives discussed within this