JK Fluid Specifications: Complete Reference Guide

Using the correct fluids in your Jeep JK is not optional. Wrong fluids cause premature wear, seal damage, and in some cases, complete component failure. This guide provides every fluid specification you need for your 2007-2018 Jeep Wrangler JK.

Bookmark this page. You’ll reference it every time you service your Jeep.

Engine Oil Specifications

Engine oil is your most frequent maintenance item. Getting it right protects your investment.

3.8L V6 (2007-2011)

Specification	Value
Capacity (with filter)	6 quarts
Viscosity	5W-20
Specification	MS-6395
Filter	Mopar 4892339AB or equivalent

The 3.8L is known for oil consumption, particularly in earlier models. Check your oil level at every fuel stop and top off as needed. Consumption of up to 1 quart per 1,000 miles is not uncommon, though excessive consumption may indicate worn valve seals or piston rings.

3.6L Pentastar V6 (2012-2018)

Specification	Value
Capacity (with filter)	6 quarts
Viscosity	5W-20 (0W-20 acceptable)
Specification	MS-6395
Filter	Mopar 4892339AB or equivalent

The Pentastar’s variable valve timing system depends on clean, quality oil. Full synthetic is strongly recommended. The 0W-20 option provides better cold-start protection in freezing temperatures without sacrificing hot-weather performance.

Recommended Oil Products

These oils meet MS-6395 specification and are proven performers for JK engines:

Avoid budget oils that don’t explicitly state MS-6395 compliance. The Chrysler specification ensures proper additive packages for your engine’s requirements.

Oil Change Intervals

Driving Conditions	Interval
Normal driving	5,000-7,500 miles
Severe duty (off-road, dusty, towing)	5,000 miles
Extended drain (full synthetic)	Up to 10,000 miles

When in doubt, change it sooner. Oil is cheap; engines are expensive.

Transmission Fluid Specifications

Transmission fluid requirements differ between automatic and manual transmissions, and using the wrong fluid causes serious problems.

Automatic Transmissions

All JK automatic transmissions (42RLE, 545RFE, W5A580) require the same fluid:

Specification	Value
Fluid Type	ATF+4
Specification	MS-9602
Capacity	8-14 quarts (varies by transmission)

Critical Warning: Do NOT substitute Dexron, Mercon, or any other automatic transmission fluid. ATF+4 has specific friction modifiers required for Chrysler transmissions. Wrong fluid causes harsh shifting, slipping, and premature failure.

For drain and fill service (not a complete flush), plan on approximately 4-5 quarts. The remaining fluid stays in the torque converter and cooler.

Manual Transmission (NSG370)

Specification	Value
Fluid Type	Mopar Manual Transmission Lubricant
Alternate	GL-3 gear oil (e.g., Royal Purple Synchromax)
Capacity	Approximately 2 quarts

The NSG370 is a Mercedes-sourced transmission that prefers lighter GL-3 fluid rather than heavy gear oil. Some owners report improved shift quality with Synchromesh or Royal Purple Synchromax.

Transmission Service Intervals

Service Type	Normal	Severe Duty
Automatic fluid change	60,000 miles	30,000 miles
Manual fluid change	60,000 miles	30,000 miles

Transfer Case Fluid Specifications

Both JK transfer cases use the same fluid, making service straightforward.

NV241OR (Rubicon) and NV241J (Non-Rubicon)

Specification	Value
Fluid Type	ATF+4
Capacity	Approximately 1.5 quarts
Drain Plug	3/8” square drive
Fill Plug	3/8” square drive

The transfer case is often overlooked during maintenance. It contains gears and chains that depend on proper lubrication, especially when engaging 4WD frequently.

Transfer Case Service Intervals

Conditions	Interval
Normal use	30,000 miles
Frequent 4WD use	15,000 miles
After water submersion	Immediately (within 24-48 hours)

If you cross water deep enough to submerge the transfer case, change the fluid as soon as possible. Water contamination destroys bearings and causes chain wear.

Differential Fluid Specifications

Differential fluid requirements vary based on whether you have open differentials, limited slip, or electronic lockers.

Front Differential (Dana 30 or Dana 44)

Specification	Value
Fluid Type	SAE 75W-85 GL-5
Capacity	Approximately 2.5 pints
Rubicon (with e-locker)	Add friction modifier

Rear Differential (Dana 44)

Specification	Value
Fluid Type	SAE 75W-85 GL-5
Capacity	Approximately 4.75 pints
With LSD	Add friction modifier
Rubicon (with e-locker)	Add friction modifier

Friction Modifier Requirements

Electronic lockers and limited slip differentials require friction modifier additive. Without it, you may experience:

• Chatter during turns
• Clunking when engaging/disengaging locker
• Premature clutch pack wear (LSD)

Add 4 oz of Mopar Limited Slip Additive or equivalent to each differential requiring it.

Recommended Differential Fluids

• Mopar SAE 75W-85
• Royal Purple Max Gear 75W-90
• Mobil 1 75W-90
• Amsoil Severe Gear 75W-90

Pros:

• Purpose-built for JK Wrangler ensures proper fitment and function
• Durable construction handles trail abuse and daily driving
• Backed by positive community reviews and trail-tested results

Cons:

• Premium pricing compared to generic aftermarket options
• May require longer lead times for specialty or popular items
• Some products require professional installation for best results

Higher quality synthetic gear oils provide better protection under extreme conditions. If you wheel hard, tow, or live in extreme climates, synthetic differential fluid is worth the upgrade.

Differential Service Intervals

Conditions	Interval
Normal use	30,000 miles
Off-road/towing	15,000 miles
After water submersion	Immediately

Water in differentials is the fastest way to destroy ring and pinion gears. Milky fluid when draining indicates contamination and requires immediate attention.

Coolant Specifications

Cooling system maintenance prevents overheating and protects against corrosion.

Coolant Type

Specification	Value
Type	OAT (Organic Acid Technology)
Color	Purple/Violet
Mix Ratio	50/50 with distilled water
Capacity	Approximately 13 quarts (total system)

Do Not Mix: OAT coolant is incompatible with traditional green (IAT) and orange (DEXCOOL) coolants. Mixing causes gel formation that clogs passages and destroys water pumps.

If you don’t know what’s in your system, a complete flush with distilled water before refilling with correct coolant is the safe approach.

Recommended Coolant Brands

Pros:

• Purpose-built for JK Wrangler ensures proper fitment and function
• Durable construction handles trail abuse and daily driving
• Backed by positive community reviews and trail-tested results

Cons:

• Premium pricing compared to generic aftermarket options

• May require longer lead times for specialty or popular items

• Some products require professional installation for best results

• Mopar OAT Coolant (purple)

• Zerex G-05

• Prestone OAT Compatible

Coolant Service Intervals

Service	Interval
Level check	Every oil change
Complete flush	100,000 miles or 5 years
Thermostat replacement	As needed (check if overheating)

Coolant System Notes

• Always use distilled water for mixing (tap water contains minerals that cause deposits)
• Pressure test the system periodically for leaks
• Inspect hoses for cracks, bulging, or soft spots
• Replace the radiator cap every 5 years (weak caps cause overheating)

Brake Fluid Specifications

Brake fluid is hygroscopic, meaning it absorbs moisture from the air. Moisture lowers the boiling point, leading to brake fade.

Brake Fluid Type

Specification	Value
Type	DOT 3
Alternate	DOT 4 (higher boiling point)

DOT 3 is the factory specification, but DOT 4 is compatible and provides higher wet and dry boiling points. For owners who tow, drive in mountains, or wheel aggressively, DOT 4 is the better choice.

Note: DOT 5 (silicone-based) is NOT compatible and should never be used.

Recommended Brake Fluids

• Mopar DOT 3/4
• Valvoline Synthetic DOT 3/4
• Motul RBF 600 (racing, high boiling point)
• ATE Super Blue (easy to see when bleeding)

Brake Fluid Service Intervals

Conditions	Interval
Normal use	45,000 miles or 3 years
Heavy use (towing, off-road)	30,000 miles or 2 years

Test brake fluid moisture content with an inexpensive tester. Replace if moisture exceeds 3% or fluid appears dark and contaminated.

For more on brake system maintenance and upgrades, see our JK brake upgrade guide.

Power Steering Fluid Specifications

Power steering systems are often neglected until they develop problems.

Power Steering Fluid Type

Specification	Value
Type	ATF+4
Capacity	Approximately 1 quart

Yes, the JK uses ATF+4 for power steering, the same fluid used in the automatic transmission and transfer case. This makes topping off convenient if you carry ATF+4 for emergencies.

Power Steering Service Notes

• Check level at every oil change
• Fluid should be red/pink and clear
• Dark or burnt-smelling fluid indicates overheating
• Foamy fluid indicates air in the system (check for leaks)

There’s no official flush interval, but replacing contaminated fluid improves pump longevity and steering feel.

Special Considerations for Modified Jeeps

Modifications change fluid requirements and service intervals.

Lifted Jeeps

• Check driveline angles; increased angles accelerate U-joint and slip yoke wear
• Shorter service intervals for transfer case if running significant lift
• Extended brake lines may require different bleeding procedures (see brake upgrade guide for details)

Larger Tires

• More stress on differentials; consider synthetic gear oil and shorter service intervals
• Increased brake wear; monitor fluid level more frequently (see brake guide for recommendations)
• Transmission works harder; consider 30,000-mile fluid changes
• Check our all-terrain tire guide for tire recommendations and their maintenance impact

Regeared Differentials

After regearing:

• Use break-in additive for first 500 miles
• Change differential fluid at 500 miles, then 1,500 miles
• Synthetic gear oil only after break-in complete

Lockers (Aftermarket)

• Air lockers: Check air line connections regularly
• Selectable lockers: Follow manufacturer’s fluid recommendations
• Automatic lockers: May require specific gear oil; check documentation

Engine Modifications

• Superchargers/turbo: Shorter oil change intervals, consider 0W-40 or manufacturer recommendation
• Cold air intakes: Check filter more frequently in dusty conditions
• Tuned engines: Follow tuner’s oil recommendations

Quick Reference Chart

Print this and keep it in your glovebox:

System	Fluid Type	Capacity
Engine (3.8L/3.6L)	5W-20 MS-6395	6 quarts
Auto Trans	ATF+4	4-5 qt (drain/fill)
Manual Trans	GL-3 MTL	2 quarts
Transfer Case	ATF+4	1.5 quarts
Front Diff	75W-85 GL-5	2.5 pints
Rear Diff	75W-85 GL-5	4.75 pints
Coolant	OAT (purple)	13 qt (system)
Brake Fluid	DOT 3/4	As needed
Power Steering	ATF+4	1 quart

The Bottom Line

Using the correct fluids is one of the simplest ways to protect your JK investment. The specifications above represent factory requirements that have proven reliable over millions of miles.

Key takeaways:

• Never substitute transmission fluid - ATF+4 only for automatics
• Don’t mix coolant types - Stick with OAT purple
• Use friction modifier where required - Prevents locker and LSD damage
• Service more frequently when wheeling - Water and dirt accelerate wear
• Quality matters - Synthetic fluids provide better protection under stress

For complete maintenance schedules and procedures, see our JK maintenance guide. Understanding what goes into your Jeep is half the battle; the other half is doing the work on schedule. For more information on brake system maintenance, see our brake upgrade guide.

Related Guides

Explore more JK upgrade guides to complement your build:

• Oil Change Intervals — oil change schedule
• Death Wobble Fixes — diagnosing and fixing death wobble
• Common Problems by Year — known issues to monitor
• Best JK Lift Kits — lift kit maintenance considerations
• Steering Stabilizer — steering component maintenance
• Best Diff Covers — differential maintenance and protection
• Electrical Guide — electrical system maintenance

Frequently Asked Questions

Can I use 5W-30 instead of 5W-20 in my JK?

While 5W-30 won’t immediately damage your engine, it’s not recommended. The JK’s variable valve timing and tight tolerances are designed for 5W-20. Using heavier oil can affect timing system operation and fuel economy. In extremely hot climates or with older high-mileage engines, some owners switch to 5W-30, but 5W-20 remains the factory recommendation.

How do I know if my differential fluid is contaminated?

When draining differential fluid, look for these signs of contamination: milky appearance (water), metallic particles (gear wear), burnt smell (overheating), or gritty texture (dirt intrusion). Clean fluid should be translucent and have a petroleum smell. Any contamination warrants immediate fluid replacement and inspection for damage.

Is synthetic oil worth the extra cost for JK?

Yes, particularly for the Pentastar engine (2012-2018). Synthetic oil provides better protection during cold starts, resists breakdown at high temperatures, and maintains viscosity longer. For off-road use where engine temperatures can spike, synthetic is particularly valuable. The extra cost is minimal compared to engine repair bills.

What happens if I use the wrong transmission fluid?

Using Dexron, Mercon, or other non-ATF+4 fluids in your JK automatic transmission causes clutch glazing, harsh shifts, slip, and premature wear. The specific friction modifiers in ATF+4 are matched to Chrysler clutch materials. Wrong fluid damage may not appear immediately but accelerates wear significantly. If wrong fluid was added, flush the system completely with ATF+4.

How can I check my coolant freeze protection?

Use an inexpensive coolant tester (hydrometer or refractometer) available at auto parts stores. Proper 50/50 mix protects to approximately -34 degrees Fahrenheit. If your freeze protection is inadequate, don’t just add concentrate. Drain some coolant and replace with properly mixed solution to reach correct protection level.