Rear Differential Lube Change Interval

[HBarlow]

This comment I'm going to make is not based on laboratory testing or lube oil engineering, just my own personal observation.

I installed a Mag-Hytec finned aluminum differential cover on my '06 when it was only days old and had 300 miles on the odometer. I was transporting RVs at the time and very quickly put 230,000 miles on the odometer.

As every Gen III owner probably know, the owner's manuals for these trucks specifies a 15,000 mile differential fluid change. I stubbornly resisted that requirement, particularly because I was putting almost that many miles on the truck each and every month.

After changing it once at around 25k miles, on the recommendation of my mechanic buddy who formerly worked several years in a Dodge dealership, I extended the change interval to 50k miles. I continued to do that without adverse effects for the almost two years and 230k total miles I owned the truck.

When I bought the new '08 I moved the Mag-Hytec cover to the new truck and just did the first differential lube change last weekend at 48k miles. The fluid was pristinely clean and there was only the tiniest amount of metal "fuzz" on the magnetic plug. I'm not towing every day with this truck like I did with the previous one but have done some towing.

In my personal opinion, it is reasonably safe to extend the differential fluid change interval to 50k if you use quality brand name synthetic fluid and have a Mag-Hytec or other brand deep finned aluminum cover.

ON EDIT: After reading a number of follow-on posts by other members who mentioned the importance of a first service, perhaps at a much lower mileage, I remembered an important detail I had overlooked. A member suggested I return and edit this post to mention an early lube service I had forgotten so here it is:

My differential was actually serviced at 350 miles, the distance from my preferred dealer back home. The OEM differential cover was removed, the factory fill was drained, and the Mag-Hytec finned aluminum cover installed. Seven fresh quarts of synthetic lube were added.

The first drain may have allowed sufficient break-in to allow new parts to wear in with each other and the early first drain may have flushed out any tiny wear particles or "debris" left over from the manufacturing and assembly process.

It might be wise for anyone w/Mag-Hytec cover who is contemplating extended service intervals to perform the first service as recommended by the manufacturer.

I'm not encouraging anyone to follow my extended service procedure. It might be considered neglect by AAM, the manufacturer. It is what I do and I have not found any negative results from my decision. Your results may vary.

 

[RonD]

I did my first change at 30000, and also added a Mag-Hytec, it was clean, I did the next one at 60000, also clean, I will go to 60000 in the future.

 

[AWise]

Agreed. I did the first change at 50k and the lube looked good. Stuck on the Mag-Hytec, put in AmsOil and wont change it again until 100K.

 

[LBARTLETT]

good information for us all Harvey

 

[HBarlow]

Good. I'm glad other members have had a similar experience and draw the same conclusion.

At around $40 or more per lube change the price of a Mag-Hytec cover begins looking a little more affordable.

 

[LBARTLETT]

do you believe 75-140 is warranted in the rear differential if you pull heavy, especially if you live where it's hot, thanks in advance on your thoughts on the fluid weight

 

[AWise]

do you believe 75-140 is warranted in the rear differential if you pull heavy, especially if you live where it's hot, thanks in advance on your thoughts on the fluid weight

There have been other threads on this recently and IIRC, Amsoilman said that they ran a test with 75-90 and 75-140 and it actually ran hotter with 75-140. I dont think you will gain anything by running the 140 oil, but I am no expert.

 

[LBARTLETT]

thanks for the info.

 

[HBarlow]

I've wondered about that. I've used both weights independently and often use a mixture of the two because the Autozones, where I always but it, usually don't have enough bottles of either weight so I buy whatever they have.

 

[mberry]

I've been changing mine at the 30K miles mark as well. At the rate I'm going it will be another 2 years before it's due for its 90K mile change. lol. I changed it the first time around 500 miles, then again at 30K and 60K with the same results as stated so far here.

As for the 140 lube, no. I would use 75W-110 Amsoil if it was consistently hot here and/or I was towing a long distance with heavy weights. I'm running the 75W-90 Amsoil now.

 

[Ken55]

I change my rear diff at the specified interval give or take a few hundred miles. In fact just did it. While I also only have some "fuzzies" on my plug in no way is the fluid as clean as the new stuff going in. Not sure I'd want to extend the interval without an analysis. Just like the oil in our engines, would we extend it on looks alone? Or just a hunch that it's ok because of the product we're using?

Maybe if someone bothered to get an analysis done it's OK for them, but we all use out trucks differently. $40. 00 ain't a lot of money, especially on the off chance the fluid got contaminated. Just my . 02

Ken

 

[HBarlow]

Engine lube oil is subjected to very different potential contamination than a differential. The engine draws in outside air containing dust, dirt, etc. in huge volumes and the combustion process creates acids, moisture, soot particles, and extreme heat.

A differential is essentially closed.

 

[HCannon]

Just bought a 98 3500 that has 160K on it. Everything looked good and no noise. The first thing, I pulled the cap off and what a mess. It had never been changed the way it looked. Everything has slack, the gears look pretty good but now it makes a noise with new oil in it (the old oil looked like grease). It is going to require a compleat rebuild that will cost the price of several oil changes. Like Ken said, $40. 00 ain't a lot of money.

 

[Hoefler]

I am a former class 7 & 8 truck mechanic, with extensive training and experience in manual transmissions and differentials. We changed the differential and transmission lube at the first oil change. Then it was usually at the 100,000 mile mark or once a year. Granted these units held on average, 5 gallons of oil and it is was dino. This was before synthetic became popular and the cost became more reasonable. I would rebuild most units around the 1,000,000 mile mark. Reusing all gears and replacing the bearings, seals, and other small consumables. In a nut shell, I would agree that the service interval for our differentials is a bit of over kill. I am going to do my first change at 30,000 miles ( I am at 29,000 ). I have checked it at every oil change and have found that it was still clean and did not smell over heated. The biggest killer of the lube is thermal break down.

 

[Jim W]

I am a retired hydraulic engineer from a large heavy equipment manufacture. I know what happens to the gears and bearings when oil breaks down. This can happen at 500 miles or longer, extreme heat is the biggest issue with oil. Another issue is the manufacturing process that will leave debris that are left behind in the housing, as the housing is machined and cleaned. Not all of the debris are removed entirely and this is why the first oil change is so important. When changing the oil there was metal debris (fuzz) on the bottom of the diff housing. I wiped out the housing and clean the gear set. I checked the tooth pattern and looked for chipped teeth or on-even wear on the teeth. None found.

I changed my rear diff fluid at 15K mark, the fluid look clean but there was metal debris in the oil. Found by a magnetic. I also installed a Mag-Hytec rear diff cover which is made out of Al and the extra oil capacity. This is extremely important for a long life of the gear set. I plan on checking the dipstick which is included in the Mag-Hytec cover, every 2k for metal debris. I am also planning on a 30k change interval for the rear diff fluid.

When pulling my 5er and pulling over at various rest stops, I would check the tires and rear diff with a heat gun. The diff temp was never over 140F ambient temp was 70F +. With this temp reading on the rear diff, the fluid should be able to be change at 30K intervals with no failure of the fluid properties.

Just my $0. 02

 

[AMink]

I just did my first one on my 06 at 48,000. There was a lot of "mud" around the magnet. Should have done it sooner, even though the gears look great. Perhaps an early, or on schedule, change after initial wear, then extend it out as use requires?

 

[NavyDood]

Using the 15,000 mile axle oil change interval that the owners manual and FSM states is a waste of money and resources. Use a top shelf Group IV or Group V synthetic lube gear lube like Amsoil, Royal purple or Redline. Heck, they are cheaper than the dealer's price on the Group III gear lubes. Our axles are filled from the factory with Synthetic even though it is a group III synthetic.

 

[amsoilman]

Differentials today are subjected to "severe" duty service and encounter more stress and heat than was seen only a few years ago, simply due to the fact the engines of today have more HP and Torque, while the differential designs have remained virtually unchanged. Extreme pressures and temperatures generated within the differentials increase stress on the lubricant and can lead to a condition known as "Thermal runaway". Gear lubricant looses viscosity, (thickness) due to the heat and loads on the gears since the only cooling effects on differentials are the air movement in and around the differentials, and the lube itself. 100 % Synthetics can reduce temperatures of the lube simply due to the moleculure structure of the lube.



As most of you may know, Viscosity is the single most important "Property" of a lubricant. Viscosity correlates to the film thickness and film strength, which keep the moving parts from contacting each other and creating increased friction which also increases temperature. In general, the higher viscosity of a lubricant, the greater protection it provides. However, a lubricant that is to thick, (Higher Viscosity) can actually run hotter simply by consuming more energy to move it, which can also increase fuel consumption. Has anyone ever felt their vehicle's sluggishness when operated in cold conditions?



A multigrade lubricant, such as a 75W-90 gear lube, are formulated with additives called "Viscosity Index (VI) improvers", which broaden a lubricants operating temperature range, and are used to ensure multi-grade viscosity performance for hot and cold temperatures. However, the "Shearing" forces within the equipment, such as a differential, can cause these additives to break down and lose viscosity, which can seriously compromise the lube's protection quality.



The "bottom line", use a high quality Synthetic lube of the proper Viscosity for the application. In my case, the differentials call for a Synthetic 75W-90 gear lube.



Wayne



The OEM's determine the optimum Viscosity grade for the specific application

 

[gjones813]

I don't know why but back in 1998 when I was hauling a 3 car trailer, I did all the maintanance on the truck but I never change the diff oil and I put at least 110,000 mile loaded and total milage was 189,000, no failure just lucky I guesse, just never thought about it.



Today, I too, watch every thing and also have a Mag-Hytec on everthing and I run RP in mine,

I think I'm comming up on 30,000 miles and I will pull a sample and take it down to the local CAT dealer and at least have a Visco done on it and report back.

 

[Wingate]

Well, if its going to fail on anybody , it will be on ME. . But, I installed my Mag Hy-Tec at 15K miles and filled it with 8 qts. ( it think) of Valvoline 75-140 synthetic and I have absolutely NO plans of changing it again until 100K. I understand the idea of changing the oil the first time after the gears wearing in, but after that, as long as heat load on the lubricant is controlled, I see no need to change it. As others have stated, it is a closed system that isn't exposed to combustion by-products. The only possible contamination source would be if I let my wife try and back the boat or sea-doos into the lake. I still cringe at the thought of my beloved Dodge disappearing underwater with my wife standing at the boat ramp wondering what happened!!!