gl4 vs gl5

[shDK]

Hi all.

I am about to do an oilchange in the gearbox (fwd manual transmission)

My manual tells me to use 75-90 api gl4 or gl5.

I think when it is posible to use both the gl5 will offer the best protection. But what do people here think? Gl4 or gl5? It is a mazda with a 5 speed gearbox.

 

[ksp7498]

The difference is that GL5 has EP (extreme pressure) additives that are needed for hypoid gears (like in the differential of a 4WD or RWD vehicle). Problem is that those additives are also corrosive to brass, which is commonly used in the synchros of manual transmissions, so in many transmissions you should not use GL5. If your transmission says it can use either one, then it does not have any yellow metal and this is not an issue.

In this case it really doesn't matter which one you use. GL5 will not offer "better" protection but it also will not hurt. Use whichever you can find at a better price.

 

[shDK]

Originally Posted By: ksp7498
The difference is that GL5 has EP (extreme pressure) additives that are needed for hypoid gears (like in the differential of a 4WD or RWD vehicle). Problem is that those additives are also corrosive to brass, which is commonly used in the synchros of manual transmissions, so in many transmissions you should not use GL5. If your transmission says it can use either one, then it does not have any yellow metal and this is not an issue.

In this case it really doesn't matter which one you use. GL5 will not offer "better" protection but it also will not hurt. Use whichever you can find at a better price.


Won, t those extra additives still be an advantage for the overall protection and maybe specially for for the diff in the gearbox?

 

[dparm]

Get a dual-rated fluid. There are gear oils that carry GL-4 and GL-5, meaning they are safe for brass parts. Motul Gear 300 comes to mind.

 

[shDK]

I am planing to use total transmission syn fe. It carryes both gl4 and gl5 as well as a lot other approvals.

 

[dparm]

Originally Posted By: shDK
I am planing to use total transmission syn fe. It carryes both gl4 and gl5 as well as a lot other approvals.



Go for it. Should work just fine.

 

[440Magnum]

Originally Posted By: shDK
Originally Posted By: ksp7498
The difference is that GL5 has EP (extreme pressure) additives that are needed for hypoid gears (like in the differential of a 4WD or RWD vehicle). Problem is that those additives are also corrosive to brass, which is commonly used in the synchros of manual transmissions, so in many transmissions you should not use GL5. If your transmission says it can use either one, then it does not have any yellow metal and this is not an issue.

In this case it really doesn't matter which one you use. GL5 will not offer "better" protection but it also will not hurt. Use whichever you can find at a better price.


Won, t those extra additives still be an advantage for the overall protection and maybe specially for for the diff in the gearbox?


No. They're made SPECIFICALLY for hypoid ring-and-pinion gears in rear-drive rear axles. Hypoid gears do not even exist in most FWD transaxles, notable exceptions being some FWD vehicles with longituinally mounted engines like the Chrysler LH series.

 

[skyactiv]

Use a GL4 fluid if you have a choice. GL5 fluids in my experience are no good in manual transmissions. GL5 fluid is more slippery and you can lose your ability to shift faster between gears without grinding. GL4 is a much better fluid to use in your application. Your gears may grind between shifts with GL5 unless you shift slow from my experience.

 

[MolaKule]

Certain Subaru's with the common manual transmission/hypoid diff specify a GL-5/GL-5 fluid such as the Motul 300 series that uses a vey high level of AW/EP additives with friction modifiers due to the common sump design.

Unless you own a Subaru with the common manual transmission/hypoid diff sump, I see no reason to use GL-5 since there are very good dedicated GL-4 MTLs, such as Redline MT-90 or Amsoil MTG.

Here is a link that may help:


Technology of Manual Transmissions and Lubricants

 

[RobS]

Originally Posted By: MolaKule
Certain Subaru's with the common manual transmission/hypoid diff specify a GL-5/GL-5 fluid such as the Motul 300 series that uses a vey high level of AW/EP additives with friction modifiers due to the common sump design.

Unless you own a Subaru with the common manual transmission/hypoid diff sump, I see no reason to use GL-5 since there are very good dedicated GL-4 MTLs, such as Redline MT-90 or Amsoil MTG.

Here is a link that may help:


Technology of Manual Transmissions and Lubricants


I was just going to say this. Every Subaru I've ever had called for a GL5 in the trans.

 

[shDK]

When searching the internet. I found out the oem mazda gearoil for the fwd models are also api gl5 approved. Allthough i get your point i believe they use oem gl5 for a reason and i will do the same.

 

[supercity]

If they say a GL4 is suitable then that is all you should need. Unless you are using the OEM fluid or an expensive synthetic GL5 product that is described as suitable for Syncromesh transmissions I would stick with GL4.

 

[shDK]

The datasheet says it it made for manual transmissions with and without syncro.

 

[440Magnum]

For a manual trans, my rule of thumb is that if it says GL 3/4/5 is OK, they're giving you permission to use the LOWEST with impunity. I'd only put GL-5 in a manual transmission if the manual says GL-5 is REQUIRED. Gear oils in MTs is a definite case of lower GL # is better, unless the higher number is mandated.

 

[shDK]

Originally Posted By: 440Magnum
For a manual trans, my rule of thumb is that if it says GL 3/4/5 is OK, they're giving you permission to use the LOWEST with impunity. I'd only put GL-5 in a manual transmission if the manual says GL-5 is REQUIRED. Gear oils in MTs is a definite case of lower GL # is better, unless the higher number is mandated.



Is that still the case when a gearoil has both api gl4 and gl5. ?

 

[MolaKule]

Quote:
Is that still the case when a gearoil has both api gl4 and gl5. ?


For what application? MTLs or Diffys?

 

[supercity]

Originally Posted By: shDK


Is that still the case when a gearoil has both api gl4 and gl5. ?


The answer is not always. GL5 is a gear oil specification, not a transmission specification. GL5 exceeds GL4 so any oil meeting GL5 will also meet GL4. That does not necessarily make it suitable for an application that calls for GL4.

 

[antiqueshell]

I'd stick with the GL-4 rating because your gearbox does NOT need the extra additives that come with GL-5.

Also it is generally accepted that GL-4 spec is better suited to the characteristics of synchronizers in the typical FWD gear box. This includes specific friction modifiers and related additives.