Wondering if anyone running synthetic gear oil in the front and rear diffs has increased their change intervals. I just dumped the oil between 20,000km changes and it looked spotless. Considering the price of synthetic should we be increasing our intervals?

Also I never noticed before a discrepancy between the shop service manual and the owners manual. Shop manual specifies standard gear oil (non-synthetic), owners manual specifies sythetic (just talking about the 75-90 here, not the upgraded towing grade oil).

Cheerio
Brett
Langley, BC

Syn gear oil requires sooner OCI's then dino gear oil.They only use syn gear oil for that 0.1 extra mpg's it gives to meet federal mpg standards but actually is not the greatest in your diff to make it last,hence the sooner OCI's.Just slpa some dino gear oil in it(85w-140 for towing or offroad) and your diff you love you and so will your wallet.Most top end axle builders for high dollar offroad axles(Currie and Hi9) only recommend dino gear oil and many car makers are actually switching back to dino gear oil like there moving away from timing belts(starting to learn there lesson).


This only goes for gear oil not engine oil or trans oil due to how the diffs are oiled.

I've run synthetic gear oil in my diffs in many different vehicles, sometimes with 100K change intervals due to laziness, and not a single failure... YMMV. I see nothing wrong with synthetic oil in them. There are some differential manufacturers that advise against it due to the limited slip aspect... our Jeeps are not one that advise against synthetics. I'd say change it every 60K with a good synthetic oil and it'll be fine. I did mine around 60K and used a LubeLocker gasket on the rear diff, and will change again at 120K. I used Mobil 1 75w140 in the rear and 75w90 in the front, and ATF+4 in the transfer case. At 120K I plan to change with the same weight except I will likely use Pennzoil synthetic since I stock mainly Pennzoil/Shell products now.

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Mike Rausch
Bear, Delaware
2006 Liberty Sport CRD 253K

I use also syn oil, 75w140 on both Cherokee and crd and replace it at 50-ish k. Looks like new, but lately I didn't go offroad too much either. I think you can do 100k easy without towing and/or offroading.

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2005 kj CRD, samco, suncoast tc, provent, Kennedy lift pump, GDE ECO full torque, 2nd gen filter head, 245/70/16 a/t tires, mopar light bar, fumoto oil valve, OEM Skid Plates, ARB Front bumper and HD OME, tru cool LPD47391 40k GVW tranny cooler (stock cooler delete), FF Dynamics e-fan and shroud, rocker arms replaced, HDS2 190F thermostat.

I also use synthetic in both of my CRDs. 50k miles is no problem.

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05CRD: GDE Hot ECU & TCM tunes, Provent, Cat filter, Facet lift pump, TransGo kit, Florida TC, Samcos, stainless brake lines, HDS thermostat, Renegade light bar,
Bilstein adjustables, Al's Gen 4.5 Arms, 235/85-16 Duratracs, DTT rear, Elocker front, EVIC+TPMS, Turbo timer, McNally pillar gauges, Weeks Stage II kit.

Just run what works for you. I have run nothing but synth in all for my diffs for years.
I put over 80k on my old landrover discover that was lifted locked and geared on 35s. When I sold it to my friend I helped him change all the fluids. And check the diffs. They looked like the day I put them in.

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05 Liberty CRD DD/ski slut
Lifted,hottune,Full exhaust
05 Mitsubish evolution SSL
450awhp/400awtq autocross slut

The Chrysler 8.25 is a pretty delicate diff. We have gone through 3 whole R&Ps in 100K miles (on Chrysler's nickel). I had to run Chrysler synthetic in order to maintain the 100K warranty, but now that it is on me, I switched to SWEPCO 212. This is really the ultimate hypoid oil. It is a petroleum based, 80W-140, with moly that does not require a friction modifier for use with clutch type LSDs. Synthetics are great for almost all applications except hypoid gears. They lack the shear strength of dino. (A little known secret is that Penske has been putting SWEPCO 203 in their Mobil 1 gear oil bottles for over 30 years.)

Our Jeep has never waded through water. When I switched to SWEPCO, there was only about 25K miles on the mopar synthetic and it was already black. However, this may reflect clutch material from the TrakLok diff. Bought a TruTrac to install shortly, so no clutches to wear out, going forward.

DOC

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2005 KJ CRD Ltd Detroit TrueTrac Bilsteins G2 GDE "HOT" ECU GDE TCM "Tow Tune" "euro" TC SEGR Weeks Elbow New HG at 130K ARPs Clean CAT aFe Filter Magnaflow Exhaust EHM Cumminos In-Tank Lift Pump Hayden Fan Clutch Nylon Fan VH Enabled with GDE lower shutoff point Recalibrated Temp Gauge Tekonsha Prodigy Sears P-1 ZDDP

My front diff fluid lasts twice as long as my rear diff. Synthetic oil in diffs = shorter intervals. Use conventional gear oil, your diff's and wallet will thank you!

thanks for the replies folks....decided to go back to regular gear oil......lots of different opinions here - if there are conflicting reoprts I tend to just go with the spec......

Spec, at least as per Chrysler, is synthetic for our Jeeps.

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Mike Rausch
Bear, Delaware
2006 Liberty Sport CRD 253K

That's not entirely true.

FSM says:

Front Axle
186FIA (Model 30) - Mopar Lubricant 80W-90

Rear Axle
8 1/4 - Mopar Gear Lubricant 75W-90 (Trailer Towing - Moopar Synthetic Gear Lubricant 75W-140)

Note: Trac-lok equipped axles require 118ml (4 oz) of limited slip additive be added to the lubricant.

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Silver 2006 KJ 2.8L CRD Limited:
GDE ECO Tune / Fumoto Valve / E-Tecno GX3123 7v Glow Plugs / 2nd Gen Fuel Head / Mishimoto RED Hoses / Rockers/Lifters @ 114k / Hayden FC + 11 Blade Nylon / Sears P1 Battery / Transgo 45RFE-HD2 Reprogramming Kit / Timken Front Bearings

We had this discussion a while back - Currie - the company that makes high performance diff/axles - will not warranty anything that's had synthetic oil used on it - they specify regular gear oil only.

I called tech support to ask why and the only real answer was - experience - diff's die with synthetic oil - and live with regular - so they changed their warranty policy.

Not sure how well that translates to the street - but I switched to regular oil.

(and my Camaro's been running dino oil forever - no problems with it)

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2005 CRD
stuff
Skeptic quod gratis asseritur, gratis negatur

X2.......................

Why my $4000 Currie RockJock60 get's filled with dino 85w-140.


If any one's looked at Hi9's website it's pretty apparent they do not want synthetic gear oil used and those are some hi priced diffs(nice though).

http://www.truehi9.com/oilingsystem2.html