Diesel Place banner

21 - 25 of 25 Posts

·
Registered
Joined
·
4 Posts
I am a big fan of changing out the intial fluids when a vehicle is new; doing the diffs and t-case around 10k miles can't be harmful, and helps flush out an manufacturing remnants. After that, though, the intervals can well be extended to at least 50k miles, and sometimes more, depending upon service severity and fluid used. Don't confuse change intervals with service intervals. You might only have to change fluids every 50k miles, but you should check the level every 10-15k miles.

As a massive generalization, you can do the changes yourself and save yourself a huge amount of money. $340 is grossly overpriced.

Here's a rundown of the must-do and should-consider topics:

Diffs - must use a GL-5 rated diff fluid with the low end of the grade around 75w (or 80w), and the high end from 90 to 140 grade; all depending upon service severity and length. "Synthetic" fluids are NOT required; they are recommended - you'll get longer service life out of them. Just about any brand will suffice, but a recent test from Amsoil showed their Severe Gear to be tops, with the Mobil 1 fluid a close second. All others were not that competitive, and fell back fairly substantially. Brand wars aside, the paper was well written, well documented, and (while sponsored by Amsoil) not entirely biased. The proper stated capacity is 2 qts in front diff, and 4 qts in the rear diff.

For t-case fluid, there's a large controversy over this. I believe the proper fluid is ATF fluid based upon (former) DEX/Mercon base stock chemistry; that's what the t-case was designed for. If you choose to "upgrade" you can use s "synthetic" ATF from one of many sources. Other people choose to use 5w-30 synthetic motor oil. There was an article written by Rockland about how the motor oil supposedly resisted evaporation better; a case of mistaken facts and little understanding of tribology. However, there is no proof that motor oil either helps or hurts the t-case. I prefer to use the factory spec'd fluid in the t-case; others don't. To each his own. There is plenty of factual basis for using the ATF; there is none other than anticdotal evidence for the motor oil; choose as you see fit. Further, those that use motor oil often overfill the t-case by 50%. The stated capacity is 2 quarts; the overfill takes 3 quarts total. Again, choose as you see fit. There is no proof that the overfilling helps anything.

What is known to "help" is proper maintenance with proper fluids. Change your fluids on a regular, reasonable basis and you'll have a vehicle that lasts a long, long time.
Can you change from ATF to 30weight for your transfer case?
 

·
Registered
Joined
·
1,409 Posts
The transfer case just has some bearings, gears, and a chain. Just about any reasonable lubricant will probably work. I was one who changed from ATF to 5-30 synthetic engine oil for awhile, when the truck was fairly new. I think it quieted it down a little when it was warm. But I changed back to Dex/Merc ATF and it's just fine. Using ATF that is compatible with what is in the transmission might be the safer thing to do in case some of the fluid found it's way back into the transmission.

Straight 30 weight? Might be a little thick when cold. That's why 5-30 synthetic was recommended by some. But ATF and especially the same ATF as in the transmission is safer. (You didn't say, but I'm assuming a 1st, 2nd, or 3rd gen truck, like 2001-2007 or so.)
 

·
Registered
Joined
·
628 Posts
I'm going to revive this thread to ask a question. Has anyone gone more than 75k miles on the engine oil by changing filters and topping off? I run the FS-2500 bypass system and Amsoil OEM filter and I can't find receipts or log book entry for an oil change for at least 74,235 miles. I should have done it around 40k, but I think I just did filters. Those miles are based on my previous two oil samples. I was looking at just doing filters again, but I'm now worried. Last oil report said all good, could run it to 40k like the previous sample, TBN was 6.5 then. I had to top up with a quart, oil since last sample has 13k on it. I just sent out another sample.

Going on a few road trips with the trailer this summer so it's getting fluids all over. T Case, F/R Diffs, Allison spin on filter, and possibly (probably) oil.
 

·
Registered
Joined
·
6,489 Posts
I'm going to revive this thread to ask a question. Has anyone gone more than 75k miles on the engine oil by changing filters and topping off? I run the FS-2500 bypass system and Amsoil OEM filter and I can't find receipts or log book entry for an oil change for at least 74,235 miles. I should have done it around 40k, but I think I just did filters. Those miles are based on my previous two oil samples. I was looking at just doing filters again, but I'm now worried. Last oil report said all good, could run it to 40k like the previous sample, TBN was 6.5 then. I had to top up with a quart, oil since last sample has 13k on it. I just sent out another sample.

Going on a few road trips with the trailer this summer so it's getting fluids all over. T Case, F/R Diffs, Allison spin on filter, and possibly (probably) oil.
So glad you posted and cannot wait to hear about your oil sample on 74,235 miles. Please do post it.

I don't put enough miles on my rig to hit the normal 10 to 12 thousand miles it usually reads out on the minder for oil changes. So, I change it within 1 to 2 years with normally less than 9,000 miles on it. I have read ALOT about the long interval oil changes with great news that I have nothing to worry about. Time does allow the oil to break down and get contaminated and that is why I run synthetic and premium filters. But nothing except opinons has yet told me I'm doing something wrong. So, looking forward to your oil analysis. (y)

Btw, I usually add anywhere from 1/2 to 1 quart in that nearly 2 years of running it before an oil & filter change. Also, ALL fluids except the transfer case (Dex 3) are synthetic in my rig. All just so I don't have to do it again for a long time.
 

·
Registered
Joined
·
628 Posts
Attached is my last oil analysis, when I sent it in I was guessing I had around 30k on that oil... but no documentation of oil change, an interstate move, wife's car got totaled and other family issues in 2018 obviously skewed that. You can see my trend line has no gaps from May 2016 - June 2018... then a gap of almost two years while I was going to school, (I drove a commuter car for that stint). My Amsoil account shows no diesel oil purchased between June 2018 - June 2021.

I believe this oil has about 20,000 miles on it. I found a more recent copy of my maintenance file, oil changed 8/15/2018. I must have had oil on hand.


643707
 
  • Like
Reactions: mp06011999
21 - 25 of 25 Posts
Top