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Re: GL-4/GL-5 gear oils a compromise? [Re: AC1DD] #5387236 03/27/20 06:30 PM
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sjd Offline
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Originally Posted by AC1DD
Bottom line if a manufacturer specifies GL-4 fluid...USE ONLY GL-4 fluid, not GL-4/5, GL-4+,ect

GL-4 is not actually "obsolete" because some manufactures STILL specify it for new cars sold today. Even if API says it is.

A MAJOR issue using some fluids that indicate GL-4/5, GL-4+ is that they will cause balky shifting in many models of cars with synchronized manual transmissions.


So you believe that modern synthetic oils that are rated GL-4/GL-5 are lying to us all?

I, and others, are successfully using the Motul Gear 300 in GL-4 applications with zero issues other than a slightly harder 1-2 shift when the transmission is cold due to cold ambient temps. Less than 10 degrees Celsius. The problem goes away after 2-3 minutes of driving. I certainly don't think it's damaging anything.

I had it in my last MX-5 in 120K with using When I drained the OEM fluid it looked awful after 25K. When I changed the Gear 300 after 75K it looked as good coming out as the new fluid.

Last edited by sjd; 03/27/20 06:30 PM.
Re: GL-4/GL-5 gear oils a compromise? [Re: sjd] #5387349 03/27/20 08:13 PM
Joined: May 2019
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AC1DD Offline
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Originally Posted by sjd
Originally Posted by AC1DD
Bottom line if a manufacturer specifies GL-4 fluid...USE ONLY GL-4 fluid, not GL-4/5, GL-4+,ect

GL-4 is not actually "obsolete" because some manufactures STILL specify it for new cars sold today. Even if API says it is.

A MAJOR issue using some fluids that indicate GL-4/5, GL-4+ is that they will cause balky shifting in many models of cars with synchronized manual transmissions.


So you believe that modern synthetic oils that are rated GL-4/GL-5 are lying to us all?

I, and others, are successfully using the Motul Gear 300 in GL-4 applications with zero issues other than a slightly harder 1-2 shift when the transmission is cold due to cold ambient temps. Less than 10 degrees Celsius. The problem goes away after 2-3 minutes of driving. I certainly don't think it's damaging anything.

I had it in my last MX-5 in 120K with using When I drained the OEM fluid it looked awful after 25K. When I changed the Gear 300 after 75K it looked as good coming out as the new fluid.


I'm suggesting that the car manufacturer knows their vehicle best and if their engineers recommend something there is a good reason for it. When the warranty is over do as you please but if you have a warranty in effect use the recommended specifications.

Re: GL-4/GL-5 gear oils a compromise? [Re: AC1DD] #5387405 03/27/20 09:16 PM
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MolaKule Offline
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Originally Posted by AC1DD
Bottom line if a manufacturer specifies GL-4 fluid...USE ONLY GL-4 fluid, not GL-4/5, GL-4+,ect

GL-4 is not actually "obsolete" because some manufactures STILL specify it for new cars sold today. Even if API says it is.

A MAJOR issue using some fluids that indicate GL-4/5, GL-4+ is that they will cause balky shifting in many models of cars with synchronized manual transmissions.


It is a fact that most fluids designed for purely GL-5 Hypoid differential applications have, on average, a higher viscosity than dedicated GL-4 rated MTF fluids of the same SAE grade.

For example, a 75W90 GL-5 Hypoid differential fluid will have a viscosity at least 3-5 cSt higher than a 75W90 dedicated MTF GL-4 fluid.

Sometimes even a slight viscosity increase of 2-3 cSt can cause extra shifting effort in cold temps.

Last edited by MolaKule; 03/29/20 06:28 PM.

Dr. Larry Fleinhardt: "You know, that term "dark matter" has always perplexed me. It fallaciously implies that the 95% of our universe that cannot be observed is some amorphous, eventless emptiness."
Amita Ramanujan: "I'm sorry?"
Dr. Larry Fleinhardt: "I guess it's all too human. Instead of admitting to the present limits of our knowledge, we just declare things to be unknowable." NUMB3RS
Re: GL-4/GL-5 gear oils a compromise? [Re: AC1DD] #5387468 03/27/20 10:33 PM
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sjd Offline
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Originally Posted by AC1DD
I'm suggesting that the car manufacturer knows their vehicle best and if their engineers recommend something there is a good reason for it. When the warranty is over do as you please but if you have a warranty in effect use the recommended specifications.


The car manufacturers have to make compromises and so do their engineers, usually dictated by cost versus any engineering reason.

However, you do make a valid point that if you want to ensure no warranty issues then yes, obviously play it safe and do what the factory recommends.

I see things differently and think there are a lot of areas where the performance/motorsports aftermarket is superior to the factory. One of these areas is fluids.

I should add that I am not affiliated with Motul in any way. I've just been a very satisfied customer for 14 years with a host of different vehicles.

Re: GL-4/GL-5 gear oils a compromise? [Re: sjd] #5387491 03/27/20 11:30 PM
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zeng Offline
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Originally Posted by sjd
Originally Posted by AC1DD
I'm suggesting that the car manufacturer knows their vehicle best and if their engineers recommend something there is a good reason for it. When the warranty is over do as you please but if you have a warranty in effect use the recommended specifications.


The car manufacturers have to make compromises and so do their engineers, usually dictated by cost versus any engineering reason.

However, you do make a valid point that if you want to ensure no warranty issues then yes, obviously play it safe and do what the factory recommends.

I see things differently and think there are a lot of areas where the performance/motorsports aftermarket is superior to the factory. One of these areas is fluids.

I should add that I am not affiliated with Motul in any way. I've just been a very satisfied customer for 14 years with a host of different vehicles.

+1
Whilst car manufacturers are basically engineer-centric in the early days, but the same cannot be said in modern days among others on lubricants-related recommendations by OEM .
Compromises are typically well considered by engineers , but corporate accountants ..............................

Last edited by zeng; 03/27/20 11:31 PM.
Re: GL-4/GL-5 gear oils a compromise? [Re: AC1DD] #5387528 03/28/20 02:25 AM
Joined: Jul 2012
Posts: 315
bachman Offline
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Originally Posted by AC1DD
Originally Posted by sjd
Originally Posted by AC1DD
Bottom line if a manufacturer specifies GL-4 fluid...USE ONLY GL-4 fluid, not GL-4/5, GL-4+,ect

GL-4 is not actually "obsolete" because some manufactures STILL specify it for new cars sold today. Even if API says it is.

A MAJOR issue using some fluids that indicate GL-4/5, GL-4+ is that they will cause balky shifting in many models of cars with synchronized manual transmissions.


So you believe that modern synthetic oils that are rated GL-4/GL-5 are lying to us all?

I, and others, are successfully using the Motul Gear 300 in GL-4 applications with zero issues other than a slightly harder 1-2 shift when the transmission is cold due to cold ambient temps. Less than 10 degrees Celsius. The problem goes away after 2-3 minutes of driving. I certainly don't think it's damaging anything.

I had it in my last MX-5 in 120K with using When I drained the OEM fluid it looked awful after 25K. When I changed the Gear 300 after 75K it looked as good coming out as the new fluid.



I'm suggesting that the car manufacturer knows their vehicle best and if their engineers recommend something there is a good reason for it. When the warranty is over do as you please but if you have a warranty in effect use the recommended specifications.


+
I've went by the same definition on vehicles since I've been driving. OEM or 'approved' options on most things. The GL-4 rings a bell. Think I went around the search on that one with an older VW and the soft metal innards.
I agree there are many good fluids out there and sure to be some that are spec'd and perform well above the mfg standards or 'warranty needs' if one wants to dabble or is beyond warranty.
I think Redline was a strong recommendation on a clutch job I had done for an older 6MT.

* Most of this stuff can be easily referenced or researched by aficionados on car forums specific to brands, models, years or certain variations. smile

Last edited by bachman; 03/28/20 02:26 AM.

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Re: GL-4/GL-5 gear oils a compromise? [Re: Bill_W] #5387823 03/28/20 11:15 AM
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Bill_W Offline OP
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I have heard good things about Redline products and Amsoil too. The Motorcraft XT-M5-QS is popular with Miata NC owners (previous model) I see Castrol makes it for Motorcraft. Of the list that MolaKule made I stopped at #1 on the list and going to try Amsoil MTF.


Slick
Re: GL-4/GL-5 gear oils a compromise? [Re: Bill_W] #5388899 03/29/20 07:47 PM
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AC1DD Offline
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Originally Posted by Bill_W
I have heard good things about Redline products and Amsoil too. The Motorcraft XT-M5-QS is popular with Miata NC owners (previous model) I see Castrol makes it for Motorcraft. Of the list that MolaKule made I stopped at #1 on the list and going to try Amsoil MTF.


Amsoil MTF is a good product!

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