RDU Fluid changed at 2,000 miles

[Bob The Builder]

Keep your paper work!!!! If you have any issues with that rear diff before the warranty expires its on the dealer.

If this happened to me, I would contact Ford and report what happened. That is not the right gear oil for the rear diff. The dealer should have known better. Another reason why I never have dealerships do my maintenance work. $150+ / hour labor is the other.

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[Geo8866]

Ok now I'm worried...

I did both PTU/ RDU a few weeks ago...

But the dealer gave me the same stuff for both. Doesn't match the RDU bottle in your post.

Opinions or explanations anyone?
I'm in Canada if that matters.

The likely answer is they gave you the wrong oil. But, just brainstorming here, any chance the oil weight is different in Canada due the colder climate?

 

[The Daley Show]

Looks like I got screwed...

From another post... Close but no cigar on the part numbers and lower down in the post different spec numbers too ...

Front PTU
XY-75W85-QL

• Motorcraft® SAE 75W-85 Premium Synthetic Hypoid Gear Lubricant is an excellent multi-purpose extreme pressure lubricant recommended by Ford Motor Company as meeting warranty requirements. It is recommended for conventional and limited-slip differentials of vehicles that specify a fluid meeting WSS-M2C942-A

Rear Differential
XY-75W-QL - Disconnect Rear Drive Unit Fluid

• Motorcraft® SAE 75W Disconnect Rear Drive Unit Fluid is specifically formulated for Ford disconnect rear drive units with a low offset hypoid gear
• Developed with a lower viscosity to improve axle efficiency and fuel economy
• Motorcraft® SAE 75W Disconnect Rear Drive Unit Fluid is formulated with synthetic base stocks, friction modifiers, antiwear, and extreme pressure additives to provide gear protection and smooth clutch operation
• Use only in Ford Disconnect Rear Drive Units
• Do not use conventional high-offset hypoid gear axles where SAE 75W-85, 75W-90, 80W-90, or 75W-140 is recommended.

 

[Meeka]

The likely answer is they gave you the wrong oil. But, just brainstorming here, any chance the oil weight is different in Canada due the colder climate?

I had my RDU & PTU changed @ my dealer in Canada & they used the 2 different proper Oils in both, cause we’re colder makes no difference.

 

[The Daley Show]

https://www.fcsdchemicalsandlubricants.com/quickref/axlelubeUS.pdf

Not unheard of to use the hypoid in the rear per this chart... But Maverick calls for the special RDU... It is US spec so thank @Meeka for confirming it's not a cold weather thing... Also found the French Canadian one... Shows the RDU specific as well.

Sigh

 

[Meeka]

https://www.fcsdchemicalsandlubricants.com/quickref/axlelubeUS.pdf

Not unheard of to use the hypoid in the rear per this chart... But Maverick calls for the special RDU... It is US spec so thank @Meeka for confirming it's not a cold weather thing... Also found the French Canadian one... Shows the RDU specific as well.

Sigh

British Columbia, just as cold as New Brunswick in winter. 75w in RDU, 75w85 in PTU. Hello to a fellow Canadian

 

[Phimosis]

Ok now I'm worried...

I did both PTU/ RDU a few weeks ago...

But the dealer gave me the same stuff for both. Doesn't match the RDU bottle in your post.

Opinions or explanations anyone?
I'm in Canada if that matters.

You should be no more worried about the viscosity of 75W-85 than you should be worried about straight 75W. Mavericks use the Dana-Spicer Advantek disconnecting RDU. It is designed to run on a proprietary “ultra low viscosity” lubricant (reports says that it is similar viscosity to 5W-20), because it has 45% less frictional losses than using traditional 90W gear oil.

But Ford decided that it didn't want to use Dana’s recommended thin oil and they wanted to stick with thick oil instead…… which means they would have to test it extensively with with 75W oil to make sure it could handle the thick oil, before sending it out into the world and seeing a ton of warranty expenses from RDU failures.

If there’s any risk from using the wrong oil weight, Ford has already committed that sin.

There is one other factor at play…. Friction modifiers. The 75W has added friction modifiers for the clutch pack to prevent slipping. The 75W-85 does not have the friction modifiers.

On my first edit, I downplayed the friction modifiers as being a non-issue since you don’t have the locking rear differential found in the Tremor, but on second thought, the disconnect for the open differential in the FX4 is still another clutch pack inside of the differential. It’s just that it is a single clutch instead of a dual clutch. The clutch pack in the front PTU works just fine with the 75W-85 without the friction modifiers. Is the rear RDU clutch going to slip without friction modifiers? This becomes an unknown.

single clutch in FX4

Twin clutch RDU in Tremor.

What I do know from personal experience (from limited slip Mustang) is that if there is too much slipping in the clutch pack during heavy use, it will overheat the clutches, glazing their surfaces, necessitating a new clutch pack.

 

[The Daley Show]

@Phimosis

That's the high quality nerd level content I was hoping for.

Thanks a million

 

[Tbone289]

You should be no more worried about 5W-85 than you should be worried about straight 75W. Mavericks use the Dana-Spicer Advantek disconnecting RDU. It is designed to run on a proprietary “ultra low viscosity” lubricant (reports says that it is similar viscosity to 5W-20), because it has 45% less frictional losses than using traditional 90W gear oil.

But Ford decided that it didn't want to use Dana’s recommended thin oil and they wanted to stick with thick oil instead…… which means they would have to test it extensively with with 75W oil to make sure it could handle the thick oil, before sending it out into the world and seeing a ton of warranty expenses from RDU failures.

If there’s any risk from using the wrong oil weight, Ford has already committed that sin.

There is one other factor at play…. Friction modifiers. The 75W has added friction modifiers for the clutch pack to prevent slipping. The 75W-85 does not have the friction modifiers.

Gear oils are rated on a completely different scale and standard than engine oil by SAE. 75W-85 gear oil is about the same viscosity as a 20-30 grade engine oil, so, similar to that 5w-20 estimate.

Where did you hear/read that Ford didn't take Dana's oil recommendation?

 

[thev8man]

I posted the results of the PTU oil change last week so I figured I post the RDU oil change. Pretty much the same results: It was properly filled at the factory (About half a quart and and half out), old fluid was cloudy, and there was sludge on the magnet. The RDU is slightly easier since there is no cover to remove and the fill plug is easier to get to.

Booyah

 

[Phimosis]

Gear oils are rated on a completely different scale and standard than engine oil by SAE. 75W-85 gear oil is about the same viscosity as a 20-30 grade engine oil, so, similar to that 5w-20 estimate.

Where did you hear/read that Ford didn't take Dana's oil recommendation?

Where did I hear this? From the Dana Spicer web site. There’s a screen capture of it in my original post.

Did Dana throw Ford under the bus and come out with a press release that said “Ford did not use our recommended lubricant”? No. That would be antagonistic and bad for business. But they clearly said that first they designed the low viscosity lubricant, then built the Advantek differential to work with that specified lubricant.

Dana is being tight lipped about what’s in their “ultra low viscosity lubricant” or what the lab analysis says about its viscosity, but Dana is claiming that it saves 45% frictional losses because the lubricant is much less viscous than than conventional gear oils.

At this point, I’ll just take Dana’s word for it and accept that their ultra low viscosity lubricant has a much lower viscosity than conventional gear oil, without actually seeing any lab results on it. Dana is at the pinnacle of the top tier of companies that make differentials and gear sets and they’ve earned my trust.

 

[Tbone289]

(reports says that it is similar viscosity to 5W-20)

I have changed the RDU fluid in my Maverick, and it appears to me to be similar viscosity to 5w-20 motor oil. Maybe 5w-30, but they're pretty close. Comparative viscosity charts agree with that for 75W gear oil at the same temperature.

Where did I hear this? From the Dana Spicer web site. There’s a screen capture of it in my original post.

I read your original post before I asked. You must be reading something into your provided information that I'm not, and that's why I asked where you heard it. I don't see anything in your posts that states that Ford is not using their recommended lubricant, so it is your own conclusion that Ford isn't using it. Considering the information you've provided, my exposure to the RDU oil, and the comparative viscosity chart, I wouldn't come to the same conclusion. In all the years I've worked on vehicles prior to the Maverick, I've never poured an oil that thin into a rear differential.

 

[KenE]

I posted the results of the PTU oil change last week so I figured I post the RDU oil change. Pretty much the same results: It was properly filled at the factory (About half a quart and and half out), old fluid was cloudy, and there was sludge on the magnet. The RDU is slightly easier since there is no cover to remove and the fill plug is easier to get to.

I posted the results of the PTU oil change last week so I figured I post the RDU oil change. Pretty much the same results: It was properly filled at the factory (About half a quart and and half out), old fluid was cloudy, and there was sludge on the magnet. The RDU is slightly easier since there is no cover to remove and the fill plug is easier to get to.

Changed my RDU & PTU yesterday at 4,100 miles on 2025 Lariet Hybrid AWD. Backed onto ramps for RDU, pulled onto ramps for PTU. RDU was underfilled, oil not really bad looking, magnetic drain plug had lots of metal shavings. My experience similar to others, no surprises. Fill & drain plugs not leaking, but not tightened to specs. PTU - Fill plug was Very tight, drain plug about same tightness as I found on RDU plugs. PTU also underfilled, no noticeable metal shavings, but old fluid had a peculiar smell. Refilling PTU awkward but doable. My Takeway - Both fluids needed changing early on, glad to have done, will likely not repeat until 30k or more miles. I'm 79 next month, hope I can still do it by then when I'm 80+ Lol.

 

[Geo8866]

Changed my RDU & PTU yesterday at 4,100 miles on 2025 Lariet Hybrid AWD. Backed onto ramps for RDU, pulled onto ramps for PTU. RDU was underfilled, oil not really bad looking, magnetic drain plug had lots of metal shavings. My experience similar to others, no surprises. Fill & drain plugs not leaking, but not tightened to specs. PTU - Fill plug was Very tight, drain plug about same tightness as I found on RDU plugs. PTU also underfilled, no noticeable metal shavings, but old fluid had a peculiar smell. Refilling PTU awkward but doable. My Takeway - Both fluids needed changing early on, glad to have done, will likely not repeat until 30k or more miles. I'm 79 next month, hope I can still do it by then when I'm 80+ Lol.

That’s great you’re still crawling under a car at 79. You’re an inspiration!

 

[dalola]

I posted recently on another thread, I did my 60K service, 3rd time to D&R the RDU & PTU. Both looked like new fluid this time, so I will push the next service to 100K. Still doing ATF every 30K.

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