Transmission and Diff Questions
Thread Starter
1st Gear
Joined: Oct 2024
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Transmission and Diff Questions
So, to preface this question, I know that what I'm about to ask has been dragged back and forth through the mud on these forums. However, a lot of what I'm reading was people still confused back in like 2006-2013 while these cars were still being manufactured.
I recently bought my car from an elderly couple (2007 Lexus IS250 Manual, 244,000km's), the vehicle itself is in immaculate condition but I'm not sure they've kept up on Tranny and Diff fluid changes at all. Now, depending on which forum I read some people say not to touch the Diff fluid at all, while others say there is an interval for it depending on if you live in Canada or USA (I live in Canada). Unless someone tells me different, I'm probably going to go forwards with replacing both fluids.
Then there is the argument of Mobil-1 vs. Amsoil vs. Royal Purple.
My Question is;
If I were to change my Transmission and Diff fluid am I okay to use Amsoil Severe-Gear 75w-90 Synthetic for both? or Should I use Severe-Gear for the Diff and Mobil-1 75w-90 Synthetic in the transmission?
Apologies if this is a loaded question, I'm just genuinely confused with everything I've read.
I recently bought my car from an elderly couple (2007 Lexus IS250 Manual, 244,000km's), the vehicle itself is in immaculate condition but I'm not sure they've kept up on Tranny and Diff fluid changes at all. Now, depending on which forum I read some people say not to touch the Diff fluid at all, while others say there is an interval for it depending on if you live in Canada or USA (I live in Canada). Unless someone tells me different, I'm probably going to go forwards with replacing both fluids.
Then there is the argument of Mobil-1 vs. Amsoil vs. Royal Purple.
My Question is;
If I were to change my Transmission and Diff fluid am I okay to use Amsoil Severe-Gear 75w-90 Synthetic for both? or Should I use Severe-Gear for the Diff and Mobil-1 75w-90 Synthetic in the transmission?
Apologies if this is a loaded question, I'm just genuinely confused with everything I've read.
Intermediate
Joined: Jan 2024
Posts: 269
Likes: 37
From: WA
So, to preface this question, I know that what I'm about to ask has been dragged back and forth through the mud on these forums. However, a lot of what I'm reading was people still confused back in like 2006-2013 while these cars were still being manufactured.
I recently bought my car from an elderly couple (2007 Lexus IS250 Manual, 244,000km's), the vehicle itself is in immaculate condition but I'm not sure they've kept up on Tranny and Diff fluid changes at all. Now, depending on which forum I read some people say not to touch the Diff fluid at all, while others say there is an interval for it depending on if you live in Canada or USA (I live in Canada). Unless someone tells me different, I'm probably going to go forwards with replacing both fluids.
Then there is the argument of Mobil-1 vs. Amsoil vs. Royal Purple.
My Question is;
If I were to change my Transmission and Diff fluid am I okay to use Amsoil Severe-Gear 75w-90 Synthetic for both? or Should I use Severe-Gear for the Diff and Mobil-1 75w-90 Synthetic in the transmission?
Apologies if this is a loaded question, I'm just genuinely confused with everything I've read.
I recently bought my car from an elderly couple (2007 Lexus IS250 Manual, 244,000km's), the vehicle itself is in immaculate condition but I'm not sure they've kept up on Tranny and Diff fluid changes at all. Now, depending on which forum I read some people say not to touch the Diff fluid at all, while others say there is an interval for it depending on if you live in Canada or USA (I live in Canada). Unless someone tells me different, I'm probably going to go forwards with replacing both fluids.
Then there is the argument of Mobil-1 vs. Amsoil vs. Royal Purple.
My Question is;
If I were to change my Transmission and Diff fluid am I okay to use Amsoil Severe-Gear 75w-90 Synthetic for both? or Should I use Severe-Gear for the Diff and Mobil-1 75w-90 Synthetic in the transmission?
Apologies if this is a loaded question, I'm just genuinely confused with everything I've read.
For the diff 75w-90 synthetic of your choice. Mobil, Amsoil, Royal Purple. The butt dyno all feels the same. 
I've ran those on an IS250 AWD front and back diffs. On the GS350 I'm currently running Amsoil.
I've ran those on an IS250 AWD front and back diffs. On the GS350 I'm currently running Amsoil.
Racer
Joined: Feb 2017
Posts: 1,266
Likes: 331
From: Ontario
Last edited by primavera; Dec 4, 2024 at 05:26 PM.
Driver
Joined: Mar 2018
Posts: 98
Likes: 30
From: Ontario
The diff oil definitely needs to be changed. Over time, any oil will lose its lubricant and detergent properties. I bought the Toyota stuff from the Lexus dealer, but have also used whatever Canadian Tire had that was vaguely the same weight (it's hard to find the 75W85 that is specified - usually, you can find 75W90 in retail stores). But yeah, change them both! And make sure you get new crush washers, and always start by undoing the fill plug (much easier to deal with a stuck fill plug before you drain the transmission!)
OP - just make sure the fluid in the gear box is fully compatible with brass as not GL-5 fluids are backwards compatible with GL-4 which typically goes in a MT.
Intermediate
Joined: Jan 2024
Posts: 269
Likes: 37
From: WA
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