Some Questions About DIY Diff Fluid Change

[Mr2raw]

Hey guys,

I have a 2017 5.0 CS, and I am looking to change my diff fluid soon. I have a few questions before getting started.

1. From reading on forums and groups, it seems like AMSOIL is the preferred gear oil. However, AMSOIL only makes the 75w90 and the 75w140 for the s550, while the owner's manual calls for 75w85 Motorcraft. My car is a daily driver. Which weight should I go with? And will it matter that it is not the same oil spec as suggested by OEM?

2. Let's say if I go for this :

https://www.amsoil.com/p/severe-gear-75w-90-svg/?code=SVGQT-EA#pills-home_0

I believe I would still need to buy the friction modifier and add it? Will it matter what brand of friction modifier I use if I decide to use AMSOIL.

3. Is there an order in adding friction modifier and the gear oil? Or it does not matter?

4. Owner's manual calls for 3.2 pint of gear oil to be added. Do we always add 3.2 pint? From reading, most people just add gear oil until it starts dripping from the fill hole. Which method should I go with? From most people's experiences, if adding until the fill hole starts dripping, is it usually less than 3.2 pint or over 3.2 pint or exact? If filling somehow less than 3.2 pint, is it still necessary to add the full 4 oz of the friction modifier or will an adjustment need to be made?

5. There are other options out there that have friction modifiers included in the oil mix already. How would I know that mix specifically will work? Just go by oil weight?

Thanks guys

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[HoosierDaddy]

Hey guys,

I have a 2017 5.0 CS, and I am looking to change my diff fluid soon. I have a few questions before getting started.

1. From reading on forums and groups, it seems like AMSOIL is the preferred gear oil.

FWIW I think BG is the most preferred with members here.

 

[JohnVallo]

Hey guys,

I have a 2017 5.0 CS, and I am looking to change my diff fluid soon. I have a few questions before getting started.

1. From reading on forums and groups, it seems like AMSOIL is the preferred gear oil. However, AMSOIL only makes the 75w90 and the 75w140 for the s550, while the owner's manual calls for 75w85 Motorcraft. My car is a daily driver. Which weight should I go with? And will it matter that it is not the same oil spec as suggested by OEM?

2. Let's say if I go for this :

https://www.amsoil.com/p/severe-gear-75w-90-svg/?code=SVGQT-EA#pills-home_0

I believe I would still need to buy the friction modifier and add it? Will it matter what brand of friction modifier I use if I decide to use AMSOIL.

3. Is there an order in adding friction modifier and the gear oil? Or it does not matter?

4. Owner's manual calls for 3.2 pint of gear oil to be added. Do we always add 3.2 pint? From reading, most people just add gear oil until it starts dripping from the fill hole. Which method should I go with? From most people's experiences, if adding until the fill hole starts dripping, is it usually less than 3.2 pint or over 3.2 pint or exact? If filling somehow less than 3.2 pint, is it still necessary to add the full 4 oz of the friction modifier or will an adjustment need to be made?

5. There are other options out there that have friction modifiers included in the oil mix already. How would I know that mix specifically will work? Just go by oil weight?

Thanks guys

Many brands of Diff Gear Oil will certainly work in the S550 Mustangs.
(Amzoil, BG, Lucas, Motorcraft, Red Line, Royal Purple)
Mostly it is a personal preference to which brand you prefer.

1. Weights: Doesn't really matter the difference between 75W 85, or 75W 90. Either is acceptable.
What may be more important is choosing between the lighter weights (75W90), or the heavier weights (85W 140). This choice should center around 2 factors: A: Racing conditions, i.e. Severe racing conditions and higher heat may determine you want the higher weight. B: Your climate you live in, i.e. if you frequently see temps dropping below 40 degrees, you will want to stick with lighter weight. (Myself I live in Central/Southern part of Florida, so I am comfortable with running the 75W 140 Diff Gear Oil.)

2. The AMZOIL gear oil you choose will/should specify if it includes friction modifier. If it doesn't you most certainly want to add it. I don't think the brand matters much, but most people buy the Ford/Motorcraft bottle.

3. It doesn't matter (Order) how you mix it as long as it gets in the diff.

4. Owners manual is correct at 3.2 pints. Myself I like to refer to the oil in ounces. 52 ounces is what that comes out to. Ford says the correct level of the fluid in the diff is 9mm Below the filler hole. (Measured with the car level). To my personal experience, I have filled my diff to the point of it running out of the hole: (60 ounces). Did I notice any difference ? No. As I ran it that way for over 4,000 miles before inspecting.

5. Most Gear Oil brands can be purchased with the modifier already in it. I have used both. I have never had any trouble with the pre-mixed Oils.

*NOTES*
When you go to change the diff fluid make sure you get the diff really warmed up/ or hot.
10-15 miles isn't enough to get it hot. More like 50 mile Interstate drive.
There is a lot of black oxide that wears off from the factory OEM gears that settles in the fluid so you want to get all of that out that you can.

Getting the new fluid into the diff is sometimes a challenge. There isn't much room to work in that area and you wont be able to squeeze it in from a rigid bottle. I'm not sure about the AMZOIL ezpack flexible containers. My preference is to pump it in. You can get an inexpensive fluid pump from Harbor Freight, which works well. (Or get the kit , below)

My personal preference for Gear Oil is BG. Better yet, Optimum Performance makes a kit with everything you need for your S550. (Gear Oil, Pump, Teflon Tape, etc.)
Ultra Guard LS (opmustang.com)

Other Reference:
Have any of you changed the MT-82 and Torsen fluids really early??? | 2015+ S550 Mustang Forum (GT, EcoBoost, GT350, GT500, Bullitt, Mach 1) - Mustang6G.com

 

[Mr2raw]

Many brands of Diff Gear Oil will certainly work in the S550 Mustangs.
(Amzoil, BG, Lucas, Motorcraft, Red Line, Royal Purple)
Mostly it is a personal preference to which brand you prefer.

1. Weights: Doesn't really matter the difference between 75W 85, or 75W 90. Either is acceptable.
What may be more important is choosing between the lighter weights (75W90), or the heavier weights (85W 140). This choice should center around 2 factors: A: Racing conditions, i.e. Severe racing conditions and higher heat may determine you want the higher weight. B: Your climate you live in, i.e. if you frequently see temps dropping below 40 degrees, you will want to stick with lighter weight. (Myself I live in Central/Southern part of Florida, so I am comfortable with running the 75W 140 Diff Gear Oil.)

2. The AMZOIL gear oil you choose will/should specify if it includes friction modifier. If it doesn't you most certainly want to add it. I don't think the brand matters much, but most people buy the Ford/Motorcraft bottle.

3. It doesn't matter (Order) how you mix it as long as it gets in the diff.

4. Owners manual is correct at 3.2 pints. Myself I like to refer to the oil in ounces. 52 ounces is what that comes out to. Ford says the correct level of the fluid in the diff is 9mm Below the filler hole. (Measured with the car level). To my personal experience, I have filled my diff to the point of it running out of the hole: (60 ounces). Did I notice any difference ? No. As I ran it that way for over 4,000 miles before inspecting.

5. Most Gear Oil brands can be purchased with the modifier already in it. I have used both. I have never had any trouble with the pre-mixed Oils.

*NOTES*
When you go to change the diff fluid make sure you get the diff really warmed up/ or hot.
10-15 miles isn't enough to get it hot. More like 50 mile Interstate drive.
There is a lot of black oxide that wears off from the factory OEM gears that settles in the fluid so you want to get all of that out that you can.

Getting the new fluid into the diff is sometimes a challenge. There isn't much room to work in that area and you wont be able to squeeze it in from a rigid bottle. I'm not sure about the AMZOIL ezpack flexible containers. My preference is to pump it in. You can get an inexpensive fluid pump from Harbor Freight, which works well. (Or get the kit , below)

My personal preference for Gear Oil is BG. Better yet, Optimum Performance makes a kit with everything you need for your S550. (Gear Oil, Pump, Teflon Tape, etc.)
Ultra Guard LS (opmustang.com)

Other Reference:
Have any of you changed the MT-82 and Torsen fluids really early??? | 2015+ S550 Mustang Forum (GT, EcoBoost, GT350, GT500, Bullitt, Mach 1) - Mustang6G.com

Very informative response. Thanks man!

 

[luc]

I always laugh when I read what people do to fill any system underneath the car , pumps , special bottles or a bunch of other contraptions, I do none of that and use gravitye to my advantage
Cut a Hole, about 2” diameter, in the bottom of the bottle of gear oil, drill 2 1/8 holes, opposed to each other on the bottom sides, run a small string trough them and knot the end together to use the string to suspend the bottle upside down
Cut the v shaped cap to have a 1/4 hole and attach to it 6 feet of clear 1/4” silicone tubing
Hang the bottle higher that the filling port, run the end on the tubing in the filling hole and finally pour in the bottle any fluid that you need to fill whatever you want to fill
Gravity will do its job and no more mess and wasting time
And you can use this bottle for years

 

[Dr. Norts]

I always laugh when I read what people do to fill any system underneath the car , pumps , special bottles or a bunch of other contraptions, I do none of that and use gravitye to my advantage
Cut a Hole, about 2” diameter, in the bottom of the bottle of gear oil, drill 2 1/8 holes, opposed to each other on the bottom sides, run a small string trough them and knot the end together to use the string to suspend the bottle upside down
Cut the v shaped cap to have a 1/4 hole and attach to it 6 feet of clear 1/4” silicone tubing
Hang the bottle higher that the filling port, run the end on the tubing in the filling hole and finally pour in the bottle any fluid that you need to fill whatever you want to fill
Gravity will do its job and no more mess and wasting time
And you can use this bottle for years

Just get a hand held fluid sucker pump.

Insert suck end into bottle of oil. Suck up. Put sucker end in diff and push the plunger. K.I.S.S method wins every time.

Your way seems like a hell of alot of work. String/cuts/backflips lol.

 

[jimmerheck]

getting ready to do this myself. Bought the BG and will use a handheld pump, just like the one I use to fill my boat outdrive. The pump is only about 6 bucks on Amazon and they work well. It takes a lot of pumps, but no big deal. Have used this same pump on tranny fills, diffs, etc. The best way is if you have a bottle that you can just squeeze the fluid in the diff, like those tall skinny one quart containers. In that case, I just cut off the tip of the nozzle end, stick a small clear (about 8" long hose) on the end and squeeze away. Just dont squeeze the hose into the diff, if the hose is too short.

 

[luc]

Just get a hand held fluid sucker pump.

Insert suck end into bottle of oil. Suck up. Put sucker end in diff and push the plunger. K.I.S.S method wins every time.

Your way seems like a hell of alot of work. String/cuts/backflips lol.

Just get a hand held fluid sucker pump.

Insert suck end into bottle of oil. Suck up. Put sucker end in diff and push the plunger. K.I.S.S method wins every time.

Your way seems like a hell of alot of work. String/cuts/backflips lol.

if you had to do that every single time, I would agree with you but, I have used the same bottle for the past 20 years, so.....no more pumping, squeezing, etc in an awkward position underneath the car....

 

[Elp_jc]

Hey gang, I'm planning to do this as well at the 6K-mile mark, along with the engine oil (did it at 1K initially). But I've seen both 9mm and until coming out of the hole. My car has the Torsen. Which of the 2 apply for the Torsen? Thank you.

As far as pouring the oil into the differential, when bottles are not the long ones with a spout (like BG and Redline), I've just poured it above a rear wheel with a long enough line of clear silicon tubing, or with a pump. With either method, you wouldn't be able to put 100% of the fluid in there, but we need to buy 2 quarts anyway, and there's enough leftover (which I always throw away anyway).

 

[JohnVallo]

Hey gang, I'm planning to do this as well at the 6K-mile mark, along with the engine oil (did it at 1K initially). But I've seen both 9mm and until coming out of the hole. My car has the Torsen. Which of the 2 apply for the Torsen? Thank you.

As far as pouring the oil into the differential, when bottles are not the long ones with a spout (like BG and Redline), I've just poured it above a rear wheel with a long enough line of clear silicon tubing, or with a pump. With either method, you wouldn't be able to put 100% of the fluid in there, but we need to buy 2 quarts anyway, and there's enough leftover (which I always throw away anyway).

Fords recommendation as stated in the workshop repair manual states 9mm below hole for all differentials for the S550. That said I did run mine 8 oz overfull (coming out the hole) without problem. However, I have heard that overfilling this axle may cause diff fluid to be expelled out the vent tube. (The vent tube on the S550 runs from the top of the rear-end cover, over to the right rear fender well area, then up. I know of one user who stated that running/racing at speed at Daytona that he found fluid was coming out from the vent tube.
Everyone has their own preference on how to get new fluid back into the diff. Whatever works the best for you, is all I can say, and I hope the input from other users in the forum continue to help others with ideas and methods that have worked for them.

 

[Elp_jc]

Thank you. What I'll do when the time comes, is check where the OEM fluid level is, and decide what to do.

 

[Nuked]

I am a fan of Motul fluids, however I haven't started to research if they offer weights for the S550. Diff and trans fluid changes are on my to do list this spring.

 

[Elp_jc]

I also have Motul DCT-F and 75w90 on top of my list. I'd have BG on top, but it's not nearly as effective on D4 trannies as it is on the previous version, and our tranny has DCT from the factory, so rather stick with that, especially when I'm not having any issues. That's why OEM fluids are 2nd on my list. I'm just changing the fluids to get rid of all the assembly and break-in crap in there. But yes, I'd like to get rid of the notchiness when cold, if possible.

 

[thornclaw]

is bg ultraguard still considered the best gear oil?
it is only gl 5 certified
i found this stuff by torco that is gl-6 and it is cheap
https://torcousa.com/products/rgo-racing-gear-oil
i've never heard of torco. any experience with this?

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