Royal Purple 75W90 vs. Store Brand Synthetic

[WondrousBread]

It's finally time to reinstall my transmission and diff into my Rx7, and it's come to the point of buying fluid. 75W90 is specced for both trans and diff, diff is a limited slip.

Best price I can find for my go to (Royal Purple) is ~25 for 1 quart at Canadian Tire.

Store brand synthetic 75W90 (Canadian Tire's "Motomaster") works out to $15 per quart.

As I need 4 quarts to fill both, this equates to $100 for the Royal Purple vs. $60 for the Motomaster, which is an appreciable difference. The diff also needs LSD additive, which is say $10 per bottle, so call it a $30 difference. $30 is not inconsequential to me, as I need other parts still. However, if the Royal Purple is going to provide increased performance in smoothness / longevity I'll spend the extra money.

Has anyone gone from a name brand of fluid to a store brand of identical specification (and certifications, from what I can tell), or vice-versa? Was there a difference?

Thanks

 

[Donald]

I have been using Amsoil products for transmission, transfer case and diff. (But not for the engine).

I would use Mobil 1 if I was not using Amsoil.

 

[csandste]

I'll get into this, even though I know nothing about RX-7's, haven't owned a manual transmission since an '02 Elantra and have never used Royal Purple.

It seems to me that RP is usually a middle-ish product with purple dye and way over priced and that most store brands, if they meet spec. are perfectly suitable. Although RP certainly has its fanboys, I can assure you, old and cheap as I am that I'll never fall for it.

 

[GZRider]

I'd go with Mobil1 or Castrol or Redline or Amsoil's gear lube before Royal Purple. Royal purple (at least to me) is the K&N of oils, over-promises performance and under delivers protection.

 

[WondrousBread]

My opinion of Royal Purple (gear oil only, I haven't used the motor oil in awhile) is largely the same, but I have been consistent with it for two reasons:

1. It is available on shelves near me
2. It is priced similarly to the other gear oils near me. eg. Royal Purple is $25 per quart. 1 quart Castrol is $22, Pennzoil is $25.

I originally picked it because www.rx7club.com has many threads about how conventional (and some synthetics, such as Mobil 1) in the transmission cause some notchiness. Our transmissions are known for that, and Royal Purple, Redline MT-90, and Amsoil seem to be known for reducing it. Why Mobil has not helped the notchiness (though this observation is entirely subjective) is unknown. Royal Purple is the only one of those brands sold near me, and the cheapest. Ordering it on Amazon is even more expensive, strangely. Synchromax has also been really good in my Celica, although of course that is a different car and a different product.

I last switched from the unknown fluid the previous owner used to Royal Purple, but that transmission was on it's way out anyways so I should've just saved my money. It was definitely better than the old fluid in there, but what I'm not sure of is whether it would be better than a store brand synthetic.

The pragmatist in me says to go with store brand and not worry about it, but the other side of me says "Pay for the right product the first time or pay twice" and tells me to just get the Royal Purple that should (in theory) be ideal.

EDIT: I've looked into it further, and the store brand fluid is made by Shell for Canadian Tire and includes the LSD friction modifiers. So it is a $40 savings, and a name brand without the label. I'm going to give it a shot, will report back once my car is reassembled and I have some subjective results.

 

[Ded Mazai]

Part Source sells Mystik oils for about $10.50. They also have Red Line oils.

 

[Snagglefoot]

Firstl,y only the Canadians will be buying Motomaster, but I believe its made by Citgo. If you're bothering to ask the question why not treat yourself to Royal Purple. I don't think anyone has tested Motomaster vs Royal Purple so we'll probably never know the truth.

 

[Snagglefoot]

Originally Posted by WondrousBread
My opinion of Royal Purple (gear oil only, I haven't used the motor oil in awhile) is largely the same, but I have been consistent with it for two reasons:



EDIT: I've looked into it further, and the store brand fluid is made by Shell for Canadian Tire and includes the LSD friction modifiers. So it is a $40 savings, and a name brand without the label. I'm going to give it a shot, will report back once my car is reassembled and I have some subjective results.


Make sure you check that data. There was a change in suppliers for motor oils from Shell to Citgo. Not too sure about the gear oils but don't use old internet data.

 

[Y_K]

Actually, gear oil has been a strength of RP for a long time. Of course, Amsoil test that was paid by Amsoil and ran in Amsoil lab (not in an indpendent lab at all) proves that any other oil is inferior. If you can afford it, why not? Gear oil is not exactly a space age high tech nano material science product, any oil would do. RP is one of few who still makes and sells straight SAE 90 gear oil btw

 

[RyanY]

Originally Posted by WondrousBread


As I need 4 quarts to fill both, this equates to $100 for the Royal Purple vs. $60 for the Motomaster, which is an appreciable difference. The diff also needs LSD additive, which is say $10 per bottle, so call it a $30 difference. $30 is not inconsequential to me, as I need other parts still. However, if the Royal Purple is going to provide increased performance in smoothness / longevity I'll spend the extra money.



The RP Max Gear includes friction modifier for the diff. Used it in my Cad with no extra. It is good stuff but I don't know how it compares directly to store brand...I just noticed a slightly quieter diff than when running Valvoline. Mobil 1 is also quiet.