Royal Purple Differential Fluid?

MarshRam · Jun 25, 2017

Just changed out front and rear gears with Royal Purple. 75W-140 in rear and 75W-90 in the front. It was definitely in need! So, how many miles can I run this for.

6" Lift
35 M/T
3.21 gears
No towing

Burla · Jun 25, 2017

All depends on how you use it! Is it a commuter truck or do you tow haul? Drive it on beat up roads?

Are those containers for both difs?

MarshRam · Jun 25, 2017

Burla said:
All depends on how you use it! Is it a commuter truck or do you tow haul? Drive it on beat up roads?

Are those containers for both difs?

80 percent daily commuter on the freeway. No towing and only need FWD on the beach, maybe a few times a month, not going any faster than 10 mph.

R.L.K. · Jun 25, 2017

Wow ! That old oil looks black . How many miles on it ?

The photo of your old oil is about what I got out of my front diff alone .....
If I remember correctly I got about 1.6 qt in the front , and about 2.5 qts out of the rear .

If I was you with 35s I'd be changing every 30k or less with RP oil.

Here's a link to when I did my differentials fluids change .

http://www.ramforum.com/showthread.php?p=1276334

Hope this helps !

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Burla · Jun 25, 2017

A lot of folks don't know this but the recommended interval for difs is like 20k miles, you are using group 3 oil like you chose, I say 30k. Here's the rub, no offense and I encourage you to do your own research, but your fluid choice for the difs was probably the worst one you can make. RP consistently tests at rock bottom with lucas for difs. In many 4x4 forums, RP diff fluid is practically a swear word. The problem is, gears are the one application where you have no internal cooling features like you do with the tranny and engine. Even though there isn't combustion adding acid like the engine, the temperatures can easily get high, especially in sand. You can use a temp gun to check, anything over 240 degrees F and you are taxing any base oil not group 5, IE esters. Gimmick oils die quick in this application, it's just a fact.

An ester based fluid can easily triple you interval, even oil stop says it doubles the life of the oil in the diffs. Ester based they sell and recommend is Redline. As another decent option is Amsoil gear fluid, widely believed to use a combo of base fluids. Esters don't break down under heat and load like mineral oils. I have posted many things on gear fluids in the beginning pages of the syn thread, I posted some of the testing and white paper as well I do believe.

Must read this.

Now the downsides of these have long been corrected through time tested formulations. There are basically two oils that you can get otc that give you these benefits of esters, Redline and Motul. It is widely thought Amsoil is a sturdy oil and they use some esters, but nowhere the commitment to esters as Motul and Redline.

So from link this...

Synthetic oils have better resistance to aging and high temperatures and a longer service life than mineral oils. Depending on the base oil (SHC or PAG), the oil change intervals may be three to five times longer at the same operating temperature.

Approximate oil change intervals of gear oils at an operating temperature of 176°F (80°C) are:

Mineral oil: 5,000 operating hours
SHC oil: 15,000 operating hours (extension factor 3)
PAG oil: 25,000 operating hours (extension factor 5)

So according to machinelube.com and only a fool would argue against that, Redline would last a factor of 5 against Royal Purple or any mineral based oil as far as interval goes. So go 20k miles and keep your fingers crossed, and next time Redline your diffs up, and go 100k on it.

R.L.K. · Jun 25, 2017

Well said BBB , I couldn't agree more Sir !

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PCT · Jun 25, 2017

How many miles can redline roll for on 33, 50/50 city hwy, occasional towing, open diff

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Burla · Jun 25, 2017

That is the nice thing about Esters, you wont change the interval unless you are doing severe duty. As in running over recommended towing capacity in a 2500 and going up monster grade with monster tires. And even then it would still be double the mineral oils imo. So if you are cautious I would say a minimum interval should be 60k, and up to 100k. At some point the oil is just dirty, but actually the base oil will still be good. You can likely go over 100k, but that is where I would be changing mine, somewhere between 90 and 100k miles. Anyway, that is all I have on the matter, you can look at syn threads for old tests, or just read the link.

Follow redlines instructions for adding additives, likely nobody will need them only add if there is shudder.

MarshRam · Jun 25, 2017

R.L.K. said:
Wow ! That old oil looks black . How many miles on it ?

The photo of your old oil is about what I got out of my front diff alone .....
If I remember correctly I got about 1.6 qt in the front , and about 2.5 qts out of the rear .

If I was you with 35s I'd be changing every 30k or less with RP oil.

Here's a link to when I did my differentials fluids change .

Differential oil change - DODGE RAM FORUM - Dodge Truck Forums

Hope this helps !

Sent from my SM-G900V using Tapatalk

Bought the truck 9 months ago. Spoke to the old owner and he said he never changed it. Based on that, there was at least 37k on it. My truck required 1.16 quarts front and 2.2 in the rear. Anyhow, getting ready to order redline for our next oil change and wish I could have waited for the order for the diff. I knew it had to be bad and had time to knock it out. Seems like 30k is what everyone is saying. I'll switch it at 20k. Was nice to open it up and inspect, had no noticable shavings and gears looked great, very comfortable feeling! I'll assume the front is ok as well or at least make myself believe it! Thanks for your input.

MarshRam · Jun 25, 2017

Burla said:
A lot of folks don't know this but the recommended interval for difs is like 20k miles, you are using group 3 oil like you chose, I say 30k. Here's the rub, no offense and I encourage you to do your own research, but your fluid choice for the difs was probably the worst one you can make. RP consistently tests at rock bottom with lucas for difs. In many 4x4 forums, RP diff fluid is practically a swear word. The problem is, gears are the one application where you have no internal cooling features like you do with the tranny and engine. Even though there isn't combustion adding acid like the engine, the temperatures can easily get high, especially in sand. You can use a temp gun to check, anything over 240 degrees F and you are taxing any base oil not group 5, IE esters. Gimmick oils die quick in this application, it's just a fact.

An ester based fluid can easily triple you interval, even oil stop says it doubles the life of the oil in the diffs. Ester based they sell and recommend is Redline. As another decent option is Amsoil gear fluid, widely believed to use a combo of base fluids. Esters don't break down under heat and load like mineral oils. I have posted many things on gear fluids in the beginning pages of the syn thread, I posted some of the testing and white paper as well I do believe.

Must read this.

Now the downsides of these have long been corrected through time tested formulations. There are basically two oils that you can get otc that give you these benefits of esters, Redline and Motul. It is widely thought Amsoil is a sturdy oil and they use some esters, but nowhere the commitment to esters as Motul and Redline.

So from link this...

Synthetic oils have better resistance to aging and high temperatures and a longer service life than mineral oils. Depending on the base oil (SHC or PAG), the oil change intervals may be three to five times longer at the same operating temperature.

Approximate oil change intervals of gear oils at an operating temperature of 176°F (80°C) are:

Mineral oil: 5,000 operating hours
SHC oil: 15,000 operating hours (extension factor 3)
PAG oil: 25,000 operating hours (extension factor 5)

So according to machinelube.com and only a fool would argue against that, Redline would last a factor of 5 against Royal Purple or any mineral based oil as far as interval goes. So go 20k miles and keep your fingers crossed, and next time Redline your diffs up, and go 100k on it.

Thanks. Was going to go redline, timing was bad. Till next time... Very informative post, appreciate it!

smiley · Jun 25, 2017

I bought a 5 gallon bucket of redline diff oil 75W-140 figured it was cheaper and then I would have it on hand. I love it.

SyN · Jun 25, 2017

I honestly feel RL & Amsoil SVG are the top performers in gear oils!

JMHO!

MarshRam · Jun 26, 2017

SyN said:
I honestly feel RL & Amsoil SVG are the top performers in gear oils!

JMHO!

I completely agree after reading what Burla posted and doing more research. I found a study showing RP failed a 20 hour shear stability test. Amsoil and RL passed with flying colors and were rated at the top. "A Study of Automotive Gear Lubes" was the paper on it. Cant throw the link on because it is a pdf, but it can be found on the net. Quite disappointed about the RP, considering it was a 100 bucks for the 5 bottles. I might have been better off leaving in the oil I took out!

Royal Purple Differential Fluid?

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