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#4710006 - 03/28/18 08:16 PM What weight is best?
Mar57 Offline


Registered: 12/18/12
Posts: 49
Loc: Connecticut
The car is a Mazda Miata. Owners manual calls for 90wt. gear lube in the diff. I can't find any straight 90wt. lubes. So the question is can I use a 75-90wt. lube? Mobil 1, Valvoline etc. make a synthetic 75-90wt. and a synthetic would be my preference if that weight can be used. What do you guys think?

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#4710016 - 03/28/18 08:22 PM Re: What weight is best? [Re: Mar57]
spasm3 Online   content


Registered: 05/30/10
Posts: 8776
Loc: North Carolina
I would check what the dealer has. If its 75-90 or 80w90 as well, then use what you want. If they have a straight 90wt( i doubt it) buy that.
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#4710037 - 03/28/18 08:34 PM Re: What weight is best? [Re: Mar57]
Chris142 Online   content


Registered: 06/05/03
Posts: 16965
Loc: Deplorable in apple valley, ca
Any 75w90 or 80w90 is fine.
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#4710052 - 03/28/18 08:55 PM Re: What weight is best? [Re: Mar57]
Warstud Offline


Registered: 09/02/05
Posts: 5495
Loc: MIchigan
Originally Posted By: Mar57
Owners manual calls for 90wt.


They don't mean straight 90wt.

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#4710058 - 03/28/18 09:05 PM Re: What weight is best? [Re: Mar57]
Mar57 Offline


Registered: 12/18/12
Posts: 49
Loc: Connecticut
"They don't mean straight 90wt."

If they didn't mean it, why print it? That's what the manual says so why should someone have to try to interpret what they mean?

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#4710064 - 03/28/18 09:17 PM Re: What weight is best? [Re: Mar57]
donnyj08 Offline


Registered: 08/12/12
Posts: 3038
Loc: Cincinnati
Any 75w90 synthetic will do.
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#4710066 - 03/28/18 09:18 PM Re: What weight is best? [Re: Mar57]
Warstud Offline


Registered: 09/02/05
Posts: 5495
Loc: MIchigan
They mean 75w90 or 80w90 and not 75w140. I'm using these as examples because there the most common.

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#4710067 - 03/28/18 09:18 PM Re: What weight is best? [Re: Mar57]
ctechbob Offline


Registered: 06/12/04
Posts: 171
Loc: Athens, GA
Agreed, never had a lubrication caused problem out of a 75w-90 or 80w-90 in my 91, even with the 1/2qt capacity and the track beatings it took.
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#4710105 - 03/28/18 10:20 PM Re: What weight is best? [Re: Mar57]
Reggaemon Offline


Registered: 02/19/07
Posts: 324
Loc: Pennsylvania
What year is the Miata? In the 3 owner manuals that I checked NA,NB and NC.
The specs were...GL-5 SAE 90 80w-90 and 75w-90.
Everyone I know is using 75w-90.

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#4710252 - 03/29/18 07:33 AM Re: What weight is best? [Re: Mar57]
Donald Offline


Registered: 03/21/04
Posts: 20563
Loc: Upstate NY
Less weight is definitely best. I am trying to loose weight.
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#4710321 - 03/29/18 09:01 AM Re: What weight is best? [Re: Mar57]
artificialist Offline


Registered: 09/23/07
Posts: 8598
Loc: Florida
Many Japanese cars call for SAE 90 gear oil, but I never had a problem when replacing it with conventional 80w90 or synthetic 75w90. In the repair shops where I worked, we just used whatever XXw90 gear oil was on the shelf.
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#4710768 - 03/29/18 06:00 PM Re: What weight is best? [Re: Mar57]
JLawrence08648 Offline


Registered: 01/20/17
Posts: 256
Loc: NJ
Always synthetic in that heavy weight oil, doesn't matter the weight as long as it's close, which it is.

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