Rear FX4 Differential Fluid

[Sjurgen]

Just another (and contrary) data point for this. I have 17K miles on my early delivery 2022 FX4 (i ordered my truck on day 2). I have not towed with the truck but it has the tow package.

I had the PTU and 'RD' fluid drained and replaced today at the dealer. I was able to watch the tech dump both fluids. The PTU fluid looked great - very clear. Could still see through the fluid. Looked like week old engine oil.

The 'rear dif' fluid was dark brown and opaque but there were very few metal flakes/shavings or debris. It looked completely normal for rear dif fluid at 17k miles.

Based on how the fluid looked the tech postulated that it wouldn't need to be changed any more often then 50k miles.

LOL - i'll still change it out at 20k b/c it is cheap insurance.

How much was drained? That’s one of the overall issues. What’s filled at the factory being way less than full. (For the PTU)

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[Sjurgen]

I guess anyone can answer, lol.

If they came with the mavericks, why are most people using them again rather than fill it to the top? If it's only good for 5k miles wouldn't putting it back in last another (of the same) 5k?

Your ? Is confusing.

 

[TacoTanium]

I guess anyone can answer, lol.

If they came with the mavericks, why are most people using them again rather than fill it to the top? If it's only good for 5k miles wouldn't putting it back in last another (of the same) 5k?

Your ? Is confusing.

Example: if it came with XY-75W85-QL and you want to replace it a 5k, why would you want to put XY-75W85-QL (from a new bottle obviously) in there again? Isn't it only going to last another 5k? Unless these guys are planning to replace their PTU and RDU fluid every 5k. I'm confused too that's why I'm looking for aftermarket ones that will not sludge up and go bad quickly at much less than the suggested 30k.

 

[Ranch]

Example: if it came with XY-75W85-QL and you want to replace it a 5k, why would you want to put XY-75W85-QL (from a new bottle obviously) in there again? Isn't it only going to last another 5k? Unless these guys are planning to replace their PTU and RDU fluid every 5k. I'm confused too that's why I'm looking for aftermarket ones that will not sludge up and go bad quickly at much less than the suggested 30k.

Why would you want to change your PTU and RDU fluid every 5,000 miles?

 

[Sjurgen]

Example: if it came with XY-75W85-QL and you want to replace it a 5k, why would you want to put XY-75W85-QL (from a new bottle obviously) in there again? Isn't it only going to last another 5k? Unless these guys are planning to replace their PTU and RDU fluid every 5k. I'm confused too that's why I'm looking for aftermarket ones that will not sludge up and go bad quickly at much less than the suggested 30k.

I understand. The issue is not the oil. It’s the low level I found in my PTU, not having a break-in interval and possibly the quality of the materials & manufacturing tolerances of the PTU & to a lesser degree the RDU.

 

[TacoTanium]

Why would you want to change your PTU and RDU fluid every 5,000 miles?

I'm wondering the same thing. It seems like most are changing them our early due seeing Ford's history PTU/RDU going out before 30k miles. But I didn't understand at first why most are putting the same fluid Ford p/n back in.

I understand. The issue is not the oil. It’s the low level I found in my PTU, not having a break-in interval and possibly the quality of the materials & manufacturing tolerances of the PTU & to a lesser degree the RDU.

I see. Why not just filling it to the top? But I do see both the oil and the low level being the problems.

Some are posting pictures with gunk and sludge inside well under 30k for their PTU/RDU. That's why I didn't want to put the same stuff back and looking for aftermarket substitutes. The aftermarket premiums 75w85 and 75w combo is hard to find out there. I'm thinking going something like amsoil's 75w90 for both PTU and RDU fluids. I haven't see any comment yet for using 75w90 as substitues for both units.

 

[Kenny]

I've read this whole discussion and searched other sources and there is not much on Ford Disconnect Rear Drive Unit Fluid (XY-75W-QL) substitutes. Is there something magical about this stuff that I can't just use a quality 75W-85 synthetic oil rated GL5? If your only reason is that is what Ford recommends, it's not good enough. I need to know why. 75W-85 or 75W-90 would be a little thicker so might cost me a fraction of 1 mpg but so what. Obviously it's a better choice than 75W-140.

 

[84IM]

I'd like to also know if there is a viable substitute.
The price for the two quarts (front and rear diffs) up here in Canada is $150! Ridiculous!

 

[Kenny]

There is plenty on people substituting other oils for the PTU. I don't know anything special about the RDU.

 

[Tom 71 Maverick 24]

There is plenty on people substituting other oils for the PTU. I don't know anything special about the RDU.

I think that in both cases, you need the friction modifiers included with the proper lube/fluid to keep the clutches working smoothly and with minimal wear.

I neglected to put friction modifier in my rear diffy on my Explorer, which had an Auburn Limited slip unit inside - the rear end was noisy, semi-binding when I turned. I had to drain and refill with the correct amount of modifier along with the gear lube. Problem solved.

I would see this as an area where its best to use the recommended product or equivalent. Whatever meets the Ford specs. Otherwise, it could be a warranty issue.

 

[Montana]

Yep. It sucks. It's vague and they did it on purpose to sell their brand. Do not add friction modifiers to these fluids in our Mavericks.

 

[Tom 71 Maverick 24]

Yep. It sucks. It's vague and they did it on purpose to sell their brand. Do not add friction modifiers to these fluids in our Mavericks.

Yes, the recommended product already contains the proper modifiers built in. My case was one where it was required to add a separate product and I initially failed to do so, resulting in binding and clutch chatter. There is no need for a separate modifier because the product that meets the specs has it included. Unfortunately, it's not cheap. But we don't change these fluids very often either.

 

[Kenny]

Yep. It sucks. It's vague and they did it on purpose to sell their brand. Do not add friction modifiers to these fluids in our Mavericks.

Exactly. Not sure if Mobil 1 75W90 GL5 synthetic oil already has the modifiers or not. I know if it already has it, you should not add more as in the case of FMs, you can have too much of a good thing.

 

[Montana]

Yes, the recommended product already contains the proper modifiers built in. My case was one where it was required to add a separate product and I initially failed to do so, resulting in binding and clutch chatter. There is no need for a separate modifier because the product that meets the specs has it included. Unfortunately, it's not cheap. But we don't change these fluids very often either.

Exactly. Not sure if Mobil 1 75W90 GL5 synthetic oil already has the modifiers or not. I know if it already has it, you should not add more as in the case of FMs, you can have too much of a good thing.

I'm tempted to send a sample to Blackstone and see what they find. I just send my 2nd oil sample and I have the RDU fluid downstairs. I should do it. I just want to know what else we can use as no other fluids use that single digit scale. It's misleading.

I'll contact them and see what they say. Maybe inquiring minds have already asked them.

 

[Kenny]

What would you send them? A tiny vial of your $50 quart of Ford RDU fluid? Remember Marvel Mystery Oil? When I first started driving and working on my own pickup in the 1970s I knew very little about what went on under the hood. So every now and then just to make myself feel better, I would dump a little magic in the oil filler. I suppose that's why most people would add STP, another popular additive in the era. It made us feel better. Of course there were the racers who knew exactly what it did and used it because they had to.

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