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#507002 - 05/23/04 05:26 AM Can I mix 75W-90 with a 75W-140??
par Offline


Registered: 12/05/02
Posts: 156
Loc: usa
Hi,

My Tacoma calls for 80W-90 or 90W in the differential. I've tried 75W-90 synthetic and like using it but the differential seems to have a slight 'whine'. Maybe it's just my imagination but when I go back to a 80W-90 it just seems a little quieter on real hot days.

Can I mix 75W-90 Mobile1 with 75W-140 to thicken it up a bid at the high end? I was thinking 1.5 qt of each to make up the needed 3 qts.

Thanks.

ps. I'd like to find a readily available 80W-90 synthetic.

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#507003 - 05/23/04 06:08 AM Re: Can I mix 75W-90 with a 75W-140??
rpn453 Offline


Registered: 11/06/02
Posts: 4840
Loc: Saskatchewan
I don't think it would be a problem. If they carry the same API rating they'll be compatible.

What kind of 75W-90 did you try? Have you tried anything else? What's the mileage on that diff?

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#507004 - 05/23/04 07:02 AM Re: Can I mix 75W-90 with a 75W-140??
Titanium_Alloy Offline


Registered: 06/21/03
Posts: 324
Loc: California
I don't think that using good quality synthetic 75W-90 will cause any problems in Toyota. Our Kia Sportage rear and front differentials call for 80W-90 or a straight 90 weight. I'm using Mobil 1 75W-90 without any problems and very happy with it. A number of people on this site also reported that they are using different brands synthetic gear oils 75W-90 instead of 80W-90 in their Toyotas without any problems. If you really want to stay with factory recommended grades I suggest you go with Amsoil's 80W-90.

Regards,

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#507005 - 05/25/04 04:57 AM Re: Can I mix 75W-90 with a 75W-140??
ssls6 Offline


Registered: 12/30/02
Posts: 45
Loc: Dallas TX
75w-140 probably has the viscosity of a straight 90 weight at 100c. I would just use the 75w-140 and not mix them.

...RLK

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#507006 - 05/25/04 05:32 AM Re: Can I mix 75W-90 with a 75W-140??
MolaKule Offline


Registered: 06/05/02
Posts: 14116
Loc: Midwest
quote:
Can I mix 75W-90 Mobile1 with 75W-140 to thicken it up a bid at the high end? I was thinking 1.5 qt of each to make up the needed 3 qts.

I would not recommend mixing because you don't know what you're going to get in terms of viscosity, etc.

Gear Lubes of different weights have different viscosity base fluids that make up the target weight with varying amounts of VII's. When mixing, gear lubes aren't as simple as motor oils.

As Titanium suggested, go with something like Amsoil 80W90 or go with the 75W140, but not both.

If you want a really heavy duty 75W90, go wth Schaeffer's #267.

[ May 25, 2004, 08:34 PM: Message edited by: MolaKule ]

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#507007 - 05/25/04 11:40 AM Re: Can I mix 75W-90 with a 75W-140??
wulimaster Offline


Registered: 02/07/03
Posts: 1011
Loc: Montgomery, Alabama
I just drained out my 80w90 Amsoil and 75w90 Amsoil out of the rear and transfer case and replaced with 75w90 Series 2000 and my fuel economy has improved. the old fluid was probably still good at about 100k miles but I just wanted to see if the series 2000 would make a difference.

BTW. The whine you hear could be the chain in the transfer case. Unless you have a 2wd.

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#507008 - 05/25/04 05:55 PM Re: Can I mix 75W-90 with a 75W-140??
unDummy Offline


Registered: 02/01/03
Posts: 8756
Loc: RI
The SAE J306 cst visc spec for 140wt @100c is 24 or more.
Mobil1 75w140 is ~25 according to their website.

I say run the 75w140 all by itself. Its only 1 cst from being a 90wt.

The 75w90 is ~15 cst @100c with a SAE requirement between 13.5 and 24. It is thin for a 90w.

I'm under the impression that simple math can't be used for figuring cst when homebrewing. But, 50:50 should still be a 90wt. Even at 75thick:25thin ratio would most likely qualify as a 90wt.

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#507009 - 05/25/04 08:00 PM Re: Can I mix 75W-90 with a 75W-140??
wulimaster Offline


Registered: 02/07/03
Posts: 1011
Loc: Montgomery, Alabama
quote:
Originally posted by unDummy:
The SAE J306 cst visc spec for 140wt @100c is 24 or more.
Mobil1 75w140 is ~25 according to their website.

I say run the 75w140 all by itself. Its only 1 cst from being a 90wt.

The 75w90 is ~15 cst @100c with a SAE requirement between 13.5 and 24. It is thin for a 90w.

~15cst is the norm for 90w gear oils and 25cst is the norm for 140w gear oils. You would be hard pressed to find any that vary more than 1 cst from these norms.

I opted for the fuel savings using a 75w90 synthetic over the factory 75w140 synthetic in my Excursion and would just use the 75w90 synthetic for your Toyota.

[ May 26, 2004, 11:03 AM: Message edited by: wulimaster ]

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#507010 - 05/25/04 10:04 PM Re: Can I mix 75W-90 with a 75W-140??
MolaKule Offline


Registered: 06/05/02
Posts: 14116
Loc: Midwest
Is Par still with us or did he go ask the same question on another board?

FWIW, in our area O'Reilley's has a brand called "StaLube" which appears to be full synth (by the label) and retails for about $26.00 per quart. It comes in both weights.

[ May 26, 2004, 01:14 PM: Message edited by: MolaKule ]

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#507011 - 05/26/04 06:49 AM Re: Can I mix 75W-90 with a 75W-140??
par Offline


Registered: 12/05/02
Posts: 156
Loc: usa
I'm still here!!!!

Thanks for all the replies.

My truck is fairly new (2001) with only 35K on it. I really don't have a problem with 75w-90, but it's like I said ... it just seems a tad quieter on really hot days with a 80w-90 oil. I've tried RP 75w-90 and RL 75w-90 and ended up with Castrol 80w-90 (non-synthetic) at the present time.

It's probably just my imagination. Maybe I should just buy a power amp, with the fuel savings from a synthetic, and turn up the stereo!

Thanks again.

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#507012 - 05/27/04 09:49 AM Re: Can I mix 75W-90 with a 75W-140??
MolaKule Offline


Registered: 06/05/02
Posts: 14116
Loc: Midwest
You're most likely hearing a coasting noise or slight "power-applied" noise due to running-in.

Again, If you want a really heavy duty 75W90, go with Schaeffer's #267.

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