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#1081576 - 02/07/08 10:40 PM Why is mixing gear oils bad?
Ringe Offline


Registered: 03/03/07
Posts: 55
Loc: Colorado
I did a search for this topic and couldn't find anything...could be my inept searching skills, so sorry if this has already been hashed out, but...

I am a member of a large Subaru message board, and a member there has what he calls a "Cocktail" of different fluids to use in place of a single gear oil in WRX manual transmissions. The idea is basically to mask certain poor shifting characteristics or create a bandaid fix for real syncro wear or damage.

I know the owner's manual states not to mix gear oils from different manufacturers; I assume this is because there is not miscibility standard with gear oil as there is with motor oil? Or is there really a cataclysmic chemical reaction that can occur?

Also, just for fun here is the cocktail recipe for you to know what I'm talking about:

1qt Redline lightweight shockproof
1qt Pennzoil Synchromesh
2qt Castrol HypoyC 80w-90


I think this is the latest evolution, anyway.
_________________________
~Ringe
2007 WRX 98,000mi
Stg 2, COBB intake.

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#1081707 - 02/08/08 08:02 AM Re: Why is mixing gear oils bad? [Re: Ringe]
Pablo Offline


Registered: 10/28/02
Posts: 46694
Loc: Duvall WA - Pacific NW USA
cataclysmic

Wow. cool!! Sorry.

First of all the baseoils should mix fine. That's not the problem. Second of all, a MT is a lot more tolerant of a homebrew than say a differential.

I have zero problems, say mixing MTF with MTG, or MTL and MT-90 which isn't really what you are asking but I thought I'd puke it up.

So my opinion? I don't like the blend given. Isn't the Shockproof a VERY different super Calcium oil? And the Castrol is a standard HD sulfur laden dino gear oil? It might shift OK, but he may want to run a UOA soon. Mola can provide some good info here.

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#1081930 - 02/08/08 02:22 PM Re: Why is mixing gear oils bad? [Re: Ringe]
PT1 Offline


Registered: 02/06/07
Posts: 5746
Loc: near the mistake
1qt Redline lightweight shockproof
1qt Pennzoil Synchromesh
2qt Castrol HypoyC 80w-90


I wouldn't...way too many different ingredients there from 3 different makers who all have different formulas. You might get 1+1+2= 1.5 in performance. The chances you would get 1+1+2+>4 is astronomical.
_________________________
Oils well that ends well...

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#1081954 - 02/08/08 03:07 PM Re: Why is mixing gear oils bad? [Re: PT1]
Ringe Offline


Registered: 03/03/07
Posts: 55
Loc: Colorado
Yeah, seems scary to me as well.

I think I'll put my money where my mouth is and send out a sample for a VOA sometime soon. I would imagine the viscosity would be pretty whack, with way too much sulfur and other EP additives in it.
_________________________
~Ringe
2007 WRX 98,000mi
Stg 2, COBB intake.

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#1082096 - 02/08/08 06:01 PM Re: Why is mixing gear oils bad? [Re: Ringe]
MolaKule Offline


Registered: 06/05/02
Posts: 14658
Loc: Midwest
The friction modifiers in the mtf fluids are going to be pre-empted by the fm's in the differential lubes.

I recommend against this practice for mt's. For differentials, mix differential fluids only and break a leg.
_________________________
Just pour the coffee and back away slowly! smile

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#1082143 - 02/08/08 07:07 PM Re: Why is mixing gear oils bad? [Re: MolaKule]
mechtech2 Offline


Registered: 09/05/06
Posts: 19479
Loc: Chicago Area
Mola's post is short but says it all.

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#1082167 - 02/08/08 07:39 PM Re: Why is mixing gear oils bad? [Re: PT1]
Titan Offline


Registered: 10/04/05
Posts: 2329
Loc: Morgan, UT
 Originally Posted By: PT1
You might get 1+1+2= 1.5 in performance. The chances you would get 1+1+2+>4 is astronomical.


Excellent illustration!
_________________________
The terms "dino,synthetic,blend,conventional" are marketing derived; not scientific.

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#1082183 - 02/08/08 08:10 PM Re: Why is mixing gear oils bad? [Re: MolaKule]
Ringe Offline


Registered: 03/03/07
Posts: 55
Loc: Colorado
 Originally Posted By: MolaKule
The friction modifiers in the mtf fluids are going to be pre-empted by the fm's in the differential lubes.

I recommend against this practice for mt's. For differentials, mix differential fluids only and break a leg.


For reference, the Subaru transmission requires GL-5 gear oil, due to the fact that the front differential is in the same bath as the transmission gears. So we have to run something that will protect the hypoid diff.

So that being said, what are the main differences between MTF and differential lubes in term of friction modifiers?
_________________________
~Ringe
2007 WRX 98,000mi
Stg 2, COBB intake.

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#1082190 - 02/08/08 08:27 PM Re: Why is mixing gear oils bad? [Re: Titan]
MolaKule Offline


Registered: 06/05/02
Posts: 14658
Loc: Midwest
If you mix them in various combinations, you have >= to 9 ways to make mistakes.
_________________________
Just pour the coffee and back away slowly! smile

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#1082433 - 02/09/08 10:37 AM Re: Why is mixing gear oils bad? [Re: MolaKule]
biomed_eng_2000 Offline


Registered: 08/05/06
Posts: 276
Loc: CA
If the cocktail improves shifting, then use it.

The only unknown would be the long term wear characteristics but I think that since all three ingredients are from major companies, there will be very little chance of accelerated wear.
_________________________
1999 Lexus LS400 120k+ miles, German Castrol 0W30
2005 Toyota Sienna 90k+ miles, Whatever Synthetic 0W20

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#1082456 - 02/09/08 11:28 AM Re: Why is mixing gear oils bad? [Re: biomed_eng_2000]
Ringe Offline


Registered: 03/03/07
Posts: 55
Loc: Colorado
 Originally Posted By: biomed_eng_2000
If the cocktail improves shifting, then use it.

The only unknown would be the long term wear characteristics but I think that since all three ingredients are from major companies, there will be very little chance of accelerated wear.


Well, according to a transmission tech who posts on the same forum it does in fact cause wear to other surfaces, as well as the syncros.
_________________________
~Ringe
2007 WRX 98,000mi
Stg 2, COBB intake.

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#1082500 - 02/09/08 01:13 PM Re: Why is mixing gear oils bad? [Re: Ringe]
MolaKule Offline


Registered: 06/05/02
Posts: 14658
Loc: Midwest
"So that being said, what are the main differences between MTF and differential lubes in term of friction modifiers?"

"Differential lubes use friction modifiers to reduce mechanical and fluid friction and add some anti-shudder friction modifier for limited slip, both very different chemical compounds.

Manual Transmission fluids use a different friction modifier for synchro engagement, a modifier that does NOT contain the same chemicals as differential lubes."
_________________________
Just pour the coffee and back away slowly! smile

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