Is syn really necessary in a Ford rear?

[02supercrew]

Hello!

1st time poster on BITOG.

I have a 02' F-150 that has a 9.75' Sterling rear end with LS.

I am really wondering if a syn 75-140 is really necessary requirement for this rear end, and I am wondering why I am supposedly not supposed to use a 85-140 Gl-5 dino (which I am currently, Valvoline gear oil to be exact)?

Personally I think that it's a bunch of BS, when on the same vehicle the front diff uses a 75-90 dino, and claims that it doesnt need to be changed for 100K.(Ford claims that 100K changes are ok for non-ls diffs, front or rear.)

What could possibly be wrong with using a conventional 85-140 in my rear end if I am changing it every 30K as per Ford recs. for a LS unit?

I've posted this question on various other Ford sites, and all I get is the ususal syn is better because it is slippier

. Some have even told me that I will grenade my rear axel inside of 10000 mi. I have several Ford 9" rears with 250K on factory juice that say other wise (I was not involved in the negligence).

Just an engineer that would like to know more...

[ June 23, 2004, 01:16 PM: Message edited by: 02supercrew ]

 

[rgl]

quote:

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What could possibly be wrong with using a conventional 85-140 in my rear end if I am changing it every 30K as per Ford recs. for a LS unit?

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My guess is nothing as long as the clutches don't chatter. I am going by WAG but I would think that maybe the clutch pack frictions are designed for synthetic and that's what they base their modifier quantity recommendations on. The manual for my F150 has NO change recommendations for either front or rear differentials. It says they're good for "life", which I take to mean the lube is good until the millisecond before the rear explodes, and that was the life of the rear. I just changed out both and put synthetic in at 31,000 and intend to keep occasionally cleaning the magnetic plug on the rear diff of metallic mud. I will probably not change it out again for another 50 or 60K unless the plug starts showing some excessive wear indications. My old Explorer manual said not to change it until 100K and that was without it being synthetic fill.

 

[MolaKule]

Since front diffs are rarely used, 75W90 is often specified.

Ford likes the Synthetic 75W140 in their rear differentials for two reasons;
Long Life and Max. protection.

You can probably go 100,000 miles on the Synthetic 75W140, but I don't recommend it.

My daughter's Explorer came with the 75W140 in rear diff and at 104,000 miles we saw that fluid was in good condition and hardly any wear on ring and pinion gears.

However, I replaced the rear diff fluid at the time with Schaeffer's #267.

The other alternative is to use dino and change more often, say 30-50,000 miles.

 

[02supercrew]

quote:

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Originally posted by MolaKule:
Since front diffs are rarely used, 75W90 is often specified.

Ford likes the Synthetic 75W140 in their rear differentials for two reasons;
Long Life and Max. protection.

You can probably go 100,000 miles on the Synthetic 75W140, but I don't recommend it.

The other alternative is to use dino and change more often, say 30-50,000 miles.

---

The newer Fords use a front center axel disconnect, so in fact there are still parts turning in the front diff even though it may not be engaged.

In Ford LS rears, even filled with syn, are still reccomended to change out the diff fluid at 30K mi.

How could there be any benifit of long life and max protection, if your changing it out the syn juice every 30K mi?

Can't the same thing be accomplished with dino for 1/4 the cost?

 

[MolaKule]

The Ford fluid change is for NORMAL service.

In my daughter's case, she rarely drove in the mountains and rarely needed four wheel drive. But from first-hand knowledge (since I did the change-out), both the fluid and differential looked excellent at the mileage stated.

Applied torque and diameter of ring gear generally determines the viscosity requirements for the diffys. Engine torque is rarely applied to the front diffy which is coasting 99% of the year and has zero applied torque during that 99%
of the time.

LSD's require 30k changes because the fluids are being sheared quite a bit by the LS clutch system, whether cone or plate.

Your personal economics determine whether to use synthetics and go the max, or use dinos and change more often.

[ June 23, 2004, 03:03 PM: Message edited by: MolaKule ]

 

[02supercrew]

I must have not made the point of my argument very clear, or maybe I just have my head in the sand.

I am not contesting reasons for choosing weights, reasons for changing, how long open diffs can go etc, and all the engineering, as I all ready understand that. I also realize the reasoning behind the change regime on LS units.

My question is:

If a dino gear oil can provide all the properties required for lubrication of a LS unit for 30K intervals, what are the specific benefits of using a syn gear oil for the same interval?

To me, Fords requirement of a syn in a LS unit with 30k changes is like using a F-650 to haul a golf cart.

I guess this is going to boil down to the same syn v dino motor argument with the same OCIs.

 

[rgl]

I am curious, what part of your manual says to change at 30K and how does it say it? I don't have a 2002 manual handy. I have a 2000 F-150 manual and it says under capacities that the rear axle is filled with synthetic and "considered lubricated for life" and not to change unless submerged in water or suspect leaking. The 2004 "Scheduled Maintenance Guide" says nothing about changing differential fluid at 30K or any other interval I can find. I think my Haynes manual says they recommend changing at 30k.

 

[MolaKule]

quote:

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If a dino gear oil can provide all the properties required for lubrication of a LS unit for 30K intervals, what are the specific benefits of using a syn gear oil for the same interval?

---

A dino oil can provide MOST of the properties for an application and they have been doing so for many years.

Where a synthetic-based lube has advantages are:

1. in a slight increase in mileage (average 2.8%) via reduced friction and heat.
2. Longer life through reduced oxidation and better base-fluid stability. Synthetic gear lube, like engine oil, is less apt to thicken over the life of the fluid.
3. Better viscosity index means a more stable viscosity and thicker fluid film at elevated temperatures.
4. better shear stability in LSD's, since synthetic base oil molecules shear less than do dinos.
5. On the other end of point 3., synthetic lubes flow better at cold temperature ensuring lubrication at temps when dinos are almost solid, even with the best PPD adds for dino. Synthetic gear lubes are less apt to "channel" in cold weather because of their better flow characteristics.

 

[02supercrew]

Thanks Molakule, this was the type of answer that I was looking for.

 

[Jackpot01]

I know I am a new guy here, but I have a suggestion..Dino with a bottle of the Additive Friction Modifier (4 bucks at the Ford Dealer). Might be the best way to go. I smooths up my MTX-75 Transmission real nice

Eric
01 Focus Zetec - Motorcraft 5w20
99 Maxima VQ30DE - Castrol Syntec Blend 10w30

 

[RavenTai]

quote:

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Originally posted by MolaKule:

1. in a slight increase in mileage (average 2.8%) via reduced friction and heat.

---

MolaKule, is that %2.8 figure a fully tested figure from a reliable source (SAE, EPA)? Or more personal observation of your own fuel records? Both have merit but wider studies have more likelihood of translating properly into other people’s situations

Did a little math, 25k miles (a short OCI for synthetic in a diff) at 15MPG that is 1,666 gallons of gas, at $2/gal that is $3,333, %2.8 of that is $93.33, that pays for the syn in the diff and then some, in even that short OCI, my FZJ80 is full time 4WD, I have 3 differentials turning in 90wt at all times, I’ll bet I could see more savings still??

all the other points posted are just icing on the cake if the syn will pay for itself

Warning the following is pure conjecture:

I wonder if fuel mileage is the main reason Ford is interested in Synthetics in the diff. is the CAFE effect moving beyond the engine? Makes sense to be the first place Syn would show up in production, it is only a few quarts so it does not affect their bottom line as much as Syn in the engine or transmission would, it is "lubed for life" so it would not show in calculations of service costs for fleets, If I understand EPA tests right what the manufacturer uses in the fuel mileage tests must be the recommended fluid in the owners manual.

Chevy went to synthetic in rear diffs on their trucks a few years ago, just like Ford the front diff specs Dino,

[ June 25, 2004, 02:39 AM: Message edited by: RavenTai ]

 

[02supercrew]

I found the 30K reccomendation for LS's in my Ford CD service manual.

IMO, 2.8% is too easily lost in the noise of mpg calculations.

However with CAFE breathing down MFG'ers necks, I can see their reasoning behind syn.

But, IMO, I cannot justify my use of syn, especially when I am doing 30K changes on my LS unit, and the 4x cost of syn vs dino. I know that dino will provide me with the protection I need for the span of my 30K changes.

Now if I could find some reasonably priced synthetic, or had a open rear end, I would be using a full synthetic.

I dont have any beef against synthetics, I just dont think I'll get the best bang for the buck in my situation.

I noticed that Wally world is starting to market a syn 75-140 for around $6/qt (might be more, I cant remember for sure...), this may be something that I may consider.

 

[Gene K]

quote:

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Originally posted by 02supercrew:
I found the 30K reccomendation for LS's in my Ford CD service manual.

IMO, 2.8% is too easily lost in the noise of mpg calculations.

However with CAFE breathing down MFG'ers necks, I can see their reasoning behind syn.

But, IMO, I cannot justify my use of syn, especially when I am doing 30K changes on my LS unit, and the 4x cost of syn vs dino. I know that dino will provide me with the protection I need for the span of my 30K changes.

Now if I could find some reasonably priced synthetic, or had a open rear end, I would be using a full synthetic.

I dont have any beef against synthetics, I just dont think I'll get the best bang for the buck in my situation.

I noticed that Wally world is starting to market a syn 75-140 for around $6/qt (might be more, I cant remember for sure...), this may be something that I may consider.

---

Well Dodges used to come with Dino Lube in the rear axle and the manual said not to tow without changing out the rear axle lube to synthetic.

My guess is the rear axle capacity may be marginal for the GCWR they have the vehicle rated at. This would mean synthetic was required to reduce heat and handle the heat without breaking down when under max load.

Gene

 

[MolaKule]

quote:

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MolaKule, is that %2.8 figure a fully tested figure from a reliable source (SAE, EPA)? Or more personal observation of your own fuel records? Both have merit but wider studies have more likelihood of translating properly into other people’s situations

---

Synthetic fluids surpass minerals oil in oxidative stability, shearing viscosity, Durability, and EP perfromance.

Yes, and here is a table listed in a text that shows synthetic fuel economy % over a mineral gear lube for SAE 85W140 gear lubes from fleet tests:

Fleet - Miles - Fuel Economy Increase

Line Haul - 1,300,000 1.3%

Private Delivery - 113,000 8.3%

Private Delivery - 221,000 6.1%


From another source, the mechanical efficiency gained by PAO oils over mineral oils ranged from 2.2$ to 8.8%.

Another source shows that from 0 C to -60 C a 75W90 synthetic gear lube increases only 1 % in viscoity versus a mineral oil which showed a 5% viscosity increase.

In terms of wear, a reference mineral oil GL showed 680 ppm of iron wear verses 120 ppm of iron wear for a synthetic gear lube, tests were for a 100,000 mile interval and 80W140 viscosities, performed against MIL-L-2105D tests.

Pure axle efficiency for 75W90 gear lubes showed synthetics at 96.8% versus 95.5% for mineral oils.

Pure axle efficiency for 80w140 gear lubes showed synthetics at 96% versus 93.7% for mineral oils.


So yes, my data is backed up by published results.

 

[RavenTai]

Thank you,

 

[pacem]

I have a 1 ton truck and I will use "heavy duty" gear lube, synthetic, in 140 weight due to towing 10,000 lbs.

Otherwise, without heavy load in a 1/2 ton pickup, I wouldn't worry about either synth. or 140weight.

But towing changes everything.

 

[Bio-T]

I don't think Ford recommended the 75W140 for only EPA reasons. My 95 F-250 speced 75W90 in the rear diff, and has since been changed by Ford to 75W140, Syn the same as my 01 F250.

I do tow about 8K when on vacation. So I change my Rear Diffs at 30K with 75W140 Royal Purple Synthetic. Would anything else work? Probably with 30K changes, but if the 95 F-250 breaks down it is out of my pocket and the 01 is nearing that point. So I just spend the money and change it cause it makes me feel good if for no other reason.

 

[Ken2]

PAO synthetic base oil also has a high film strength than conventional base oil. For this reason I'd choose a PAO synthetic gear oil over a Group III "synthetic" gear oil.

That might help reduce gear tooth contact if the load at a micro-point on the gear teeth exceeds the film strength of the conventional oil.


Ken

 

[02supercrew]

zzziiiipppp ... installation of flame retardant suit complete....

I just run some simple numbers. 1 gallon of Valvoline dino 85-140 runs about $8.50 USD. 1 quart of M1 75-140 runs $17 at the local Checkers.

100K interval of M1 costs approx $68 (approx 4 qts).

For that same $68 I can run dino 85-140 out to 240000 mi with 30k intervals.

For me, the advantages of synthectics do not out weigh the cost of synthetic gear lubes.

I guess I just like to crawl under my truck too much.