Fluid Capacity & Fill Level in a Nutshell

g2020 · Dec 14, 2024

This is an overview of fluid capacity and fill level considerations. In-depth coverage of front & rear differential. Heavy reliance on the owner's manual and internal dealer spec sheet. Short sections for quick reading.

If you are a Jeep guru, jump ahead to sections 10 & 11. You may appreciate reading these two sections first.

Fluid Capacity & Fill Level in a Nutshell

Table of Contents

1. Fluid Capacity
2. Fluid Level
3. Other Important Checks
4. Common Knowledge
5. Differential Fluid Basics - API GL-5 & Friction Modifier
6. Differential Fluid Grades
7. Differential Fluid Compliance - Material Standards
8. Differential Fluid Compliance - Aftermarket Brands
9. Limited Warranty on Differential Fluid
10. Published Compliance Rating System
11. Aftermarket Product Data Sheets, Online Retailers, Part Numbers, and Published Compliance Rating
12. Aftermarket Product Lines Reviewed in this Post
13. MOPAR Part Numbers and Descriptions
14. References
15. Other Posts by the Same Gladiator Owner

- The focus of sections 5 through 13 is on differential fluid

Individual Sections

1. Fluid Capacity

The starting point for fluid capacity is "nominal refill capacity", which can be lower than dry capacity / dry fill capacity
The document that I trust most as a starting point for fluid capacity is the internal dealer spec sheet
Actual fluid capacity can vary depending on the condition of a component
Investigate if refill level shows a sudden or consistent decline

2. Fluid Level

Check owner's manual or this forum for proper fluid level when full (full level, or a narrow range extending below the high full level)
- Technically, "fill level" in this context should always be "full level" , but "full level" doesn't work well in the title of a post
Guidance on proper fluid level can vary slightly by component (see Fluid level and Fluid Level Checks in index of owner's manual)
Examples:
- Differential: As Jac04 said in post #3 in this thread, "approximately 1/8 inch (3mm) below the bottom edge of the oil fill hole"
- Transfer case: "...to the bottom edge of the fill hole when the vehicle is in a level position." (on p. 208 of 2020 Gladiator owner's manual)
  - Allow the fluid to stop weeping and then wipe the fill area clean before reinstalling the fill plug
Again, proper fluid level can vary; double-check the owner's manual

3. Other Important Checks

Confirm that your work surface is level
Know the Sales Code of your vehicle to determine correct grade of fluid for rear differential (on p. 234 of 2020 Gladiator owner's manual)
Check torque specifications
Optional: For differentials, use a (sacrificial) socket extension to minimize wear and tear on your ratchet and your torque wrench (a 1.5" extension is best)

4. Common Knowledge

Service intervals: As a rule of thumb, service interval for severe duty / heavy loads / off-road use is 40% to 50% of service interval for normal driving
Contamination: Extremely dusty & dirty conditions or water contamination can end the life of a fluid; check fluids if your vehicle has been subjected to extreme conditions

5. Differential Fluid Basics - API GL-5 & Friction Modifier

Front & rear differential: Fluid must comply with API GL-5 (not lower)
Friction modifier: A friction modifier additive is required for Trac-Lok limited slip (LS) rear differential
Effect of friction modifier on open / conventional / NS (non-slip) differential: On vehicles equipped with an open/conventional front differential, friction modifiers in AMSOIL Severe Gear, Mobil 1 Syn Gear Lube LS, and Valvoline Full Syn Gear Oil will not harm the front differential (all three are intended for use in conventional and LS applications)
- The debate over the effect of friction modifiers may resurface, but I am going with the "will not harm" claims made by these major manufacturers

6. Differential Fluid Grades

Off-manual guidance: SAE 75W-85 provides better fuel economy, but SAE 75W-140 offers greater durability; as a Dana Rebuild Specification, SAE 75W-140 may be used for both axles; also see items 4 & 9 in my post on Key Info

Guidance from Jeep docs:

Rear differential grade: Recommended grade for Sales Code DRZ is SAE 75W-140 (on p. 234 of 2020 Gladiator owner's manual)
Trailer towing: For any Gladiator, the internal dealer spec sheet states: "If equipped with a Trailer Tow package use...SAE 75W-140" for the rear axle/differential; in other words, if you're towing a trailer, use SAE 75W-140; otherwise, use the grade specified in the owner's manual (on p. 234 of 2020 Gladiator owner's manual)
Front differential grade: Recommended grade for all front differentials is SAE 75W-85 (see "Axles (Front)" on second-to-last page of internal dealer spec sheet)
Modified vehicles: For vehicles with modifications to the chassis or oversize tires (higher & bigger), SAE 75W-140 may be required for both differentials

7. Differential Fluid Compliance - Material Standards

MS-A0450 for lubricant, SAE 75W-85
MS-8985 for lubricant, SAE 75W-140
MS.10111 for friction modifier

8. Differential Fluid Compliance - Aftermarket Brands

As noted above, name-brand product lines such as AMSOIL Severe Gear, Mobil 1 Syn Gear Lube LS, and Valvoline Full Syn Gear Oil comply with API GL-5 and contain friction modifier additives
Not all brands are compliant with material standards:
- AMSOIL states compliance with ("Chrysler GL-5 based") specifications on their Severe Gear data sheet (I called their technical team to confirm 100% compliance with the specific MS-numbers, shown in section 7 above)
- Mobil 1 is unable to state compliance with material standards (I also called ExxonMobil and spoke with a representative)
- Valvoline accurately states compliance with one material standard number (MS-8985, for SAE 75W-140), but the product information sheet for SAE 75W-140 also mentions "MS-5630" instead of MS.10111 for the friction modifier additive

9. Limited Warranty on Differential Fluid

Unless otherwise specified, an aftermarket manufacturer's limited warranty should be valid for the same service intervals (and, for severe duty / heavy loads / off-road use, much shorter service intervals) as those stated in the vehicle owner's manual
- This is clearly stated in the Mobil 1 limited warranty ("...your vehicle’s OEM recommended oil change interval....")
- Valvoline does not publish a warranty statement, but every product sold in the United States has an implied warranty by law
AMSOIL Severe Gear is the only product line covered in this review with a (25%) higher mileage warranty (the correct box in the DATA SHEET is called "Severe Service") for severe duty / heavy loads / off-road use than the recommended service interval published in the owner's manual (see section 3.3 in my post on key takeaways)

10. Published Compliance Rating System

The following rating system has been created to evaluate statements of compliance with OEM specifications, published by aftermarket manufacturers
This system is based on the number of individual fluids, including friction modifier additive, that should be compliant with OEM specifications
The final percentage shows attainment, toward the goal of complete compliance, for published compliance
- Published OEM specification compliance is that which is stated on the label or published on a website

Published compliance rating system:

50% for industry standard API GL-5 for both grades, all-or-nothing

20% = 10% X 2 grades, for lubricant MS-number for each of the two grades

20% = 10% X 2 grades, for friction modifier MS-number for each of the two grades

10% for clear documentation on both grades, all-or-nothing

Example: The Valvoline product line, below, gets 50% for API GL-5, 10% for MS-8985, 0% for MS-A0450, 0% for MS.10111, and 0% for clear documentation for a total published compliance rating of 60%

This is an evaluation of compliance documentation, not fluid performance

11. Aftermarket Product Data Sheets, Online Retailers, Part Numbers, and Published Compliance Rating

Notes:

MOPAR is listed last for reference
Direct links for price search: Each price link is for either one grade (MOPAR) or both grades (AMSOIL, Mobil 1, Valvoline)

1. AMSOIL Severe Gear 100% Synthetic Gear Lube

Published compliance rating: 100% (API GL-5, and "any other GL-5 based Chrysler specifications")
Data sheet
Prices on online store
Product codes by grade:
- SAE 75W-85 (product code SVLPK-EA)
- SAE 75W-140 (product code SVOPK-EA)

2. Valvoline Full Synthetic Gear Oil

Published compliance rating: 60% (API GL-5, and MS-8985 for SAE 75W-140)
Product information sheets by grade:
- SAE 75W-90 (part number 889785)
- SAE 75W-140 (part number 889787)
Prices
- Prices on Summit Racing
- Prices on Walmart

3. Mobil 1 Synthetic Gear Lube LS

Published compliance rating: 50% (API GL-5)
Product information links by grade, each with link to product data sheet:
- SAE 75W-90 (part number 104361)
- SAE 75W-140 (part number 102490)
Prices
- Prices on Summit Racing
- Prices on Walmart

4. MOPAR Synthetic Gear & Axle Lubricant

Published compliance rating: 100% (OEM brand)
Material standard number (starting with MS- or MS.) stated on the label and shown below
Prices on MOPAR eStore for SAE 75W-85, SAE 75W-140, and axle additive:
- SAE 75W-85 (MOPAR 68378949AA, MS-A0450, API GL-5)
- SAE 75W-140 (MOPAR 68218657AB, MS-8985, API GL-5)
- MOPAR Limited Slip Friction ModifierAxle Additive (MOPAR 04318060AD, MS.10111)
  - For Trac-Lok limited slip (LS) anti-spin rear differential, 2.37 fl oz of limited slip friction modifier axle additive is required with use of MOPAR Synthetic Gear & Axle Lubricant

12. Aftermarket Product Lines Reviewed in this Post

AMSOIL Severe Gear 100% Synthetic Gear Lube
Mobil 1 Synthetic Gear Lube LS
Valvoline Full Synthetic Gear Oil

Notes:

The name of each product line is shown as it appears on the label (without the grade)
On its product information sheets, Valvoline uses the (longer) name Valvoline Advanced Full Synthetic Gear Oil w/ Limited Slip for this product line

13. MOPAR Part Numbers and Descriptions

MOPAR 68378949AA Synthetic Gear & Axle Lubricant SAE 75W-85, MS-A0450, API GL-5, 1-quart size
MOPAR 68218657AB Synthetic Gear & Axle Lubricant SAE 75W-140, MS-8985, API GL-5, 1-quart size
MOPAR 04318060AD Limited Slip Friction Modifier Axle Additive, MS.10111, 4 fl oz size; for Trac-Lok limited slip (LS) rear differential, 2.37 fl oz is required with use of MOPAR Synthetic Gear & Axle Lubricant