byez

Mazda recommends both. Can anyone tell me which one works best for the 6 speed or is the difference really unnoticeable?


GL-5 is for DIFFERENTIAL ONLY (LSD)

GL-4 is for Manual 6 Speed TRANSMISSON ONLY

For all RX-8's ASH8

mysql

GL5 for 3 years, got a new transmission. Now GL4 (Amsoil)

newguy

I dont know the mazda trans at all but in any trans with any brass parts like syncros it is a big no-no to use GL5, it contains additives that eat away at brass. GL4 for me and hopefully a non sulfer based fluid after reading the horror stories of trans oil stinking in the cabin right after the fluid is changed, with no real resolutions to the problem that i read

mysql

It took about 26k miles or so before my tranny developed grinding issues from the GL5. Before the grinding, the GL5 stuff felt great .. better than stock fluids.

It took another 10k miles before the grinding was so bad that the mazda techs couldn't deny there was an issue. They kept telling me they were not able to replicate the grinding.

So at 47k miles Mazda wanted the dealer to rebuild the tranny. But it was so eaten up that they decided to give me a brand new one instead.

b'Eight'

From my back ground in fluid power, I know some hydraulic fluids such as Quinta lube (a hydraulic oil which is similar to ATF) can cause "chemical attack" on bronze parts. Even parts that are zinc & bronze, the fluids will leech out the bronze and cause parts to mechanically explode / fail.

nycgps

iTrader: (1)

Use GL4 for ur tranny if u want it to live long.

newguy

Ive had GL5 especially synthetics cause grinding in other cars also, I believe it is to slippery and fails to let the syncros do thier job and line up quickly, b/c theyre too slick to engage quickly this causes you to grind by engaging the next gear too quickly eventually wearing down the gears. I switched back to Redline GL4 and after a flush and things improved

mysql

I couldn't find anything besides GL5 and GL4/GL5 fluids in local auto stores. I ended up having to order amsoil from online... craziness.

olddragger

iTrader: (3)

doesnt this increased wear only come if you are trying to shift faster than the syncos can line up? Or is this regardless how fast you shift?
I have 60K on my trans and other than a little reverse noise and very little whining in 4th and 6th while cold---i'm good.
I think the noise is more of a result of the short shifter--than the trans
i have always used rp 75/90 mixed with rp 85/140 half and half.
OD

Icemark

that is only applicable if the gear oil exceeds 225F/250F.

Yeah, the solution is not to overfill the tranny or try and fill the tranny from the shifter (which some shops try and do). If you spill the oil on the boots, they will absorb it and let out the fumes from the heat when driving.

ZumnRx8

the first one. GL5

Icemark

GL-4 gear lubes have half the extreme pressure additives of GL-5 lubes... it does not change anything with how slippery a gear oil is.

API service classifications range from GL-1 through GL-5, with the number indicating level of service severity. GL-1 is the least severe, and its requirements are normally satisfied with motor oil. GL-2 requirements are met with rust and oxidation inhibited oils. GL-3 through GL-5 require the addition of extreme pressure (EP) additives, with higher GL numbers indicating a higher level of EP additive. That is the only difference.

According to the API: GL-4 is spec'd for Manual transmissions, spiral bevel and hypoid gears in moderate service, while GL-5 is spec'd for moderate and severe service on hypoid and other types of gears and may also be used in manual transmissions.

Now I have seen some major issues with RP gear lubes in rear ends (mostly from viscosity break down and etching on non steel parts) and I can not recommend RP use as gear oil... perhaps that is the GL5 issue you are confusing. Were you using RP gear lube before?

mysql

yes, rp maxgear.

I haven't had any issue with maxgear in the diff though.

olddragger

iTrader: (3)

yea i went with mobil 1 in the diff--still have rp max in trans but a heavier weight.--change it every year.
OD

LionZoo

Next time I change my gear oil, which should be in a few months, I'll try a Motorcraft synthetic blend that the Miata guys say is very helpful in curing any grinds and is supposedly specifically formulated for NB 6 speeds of which the 2004-2008 RX-8 transmission is a variation of. I'll check back when I do.

newguy

Im new to the mazda trans, do you guys use these brands in the GL4 or GL5 rating? Ive used mobil1 in the past also with no problems in other cars and I hear good things about the ford fluids

Icemark

Pricey stuff... last I checked almost $35 a quart.

Icemark

Yeah, the RP max gear tends to etch brass and copper which will lead to shifting issues, as well as breaks down under high shear loads (up to 40% loss in viscosity during the KRL Shear Stability Test).



Ideally a good quality gear oil will be in the gray area before and after the test. Lucas 75/90 Synthetic, at 22.35 cSt, and Royal Purple Max-Gear 75W-90, at 19.32 cSt, both exceed the maximum 18.49 cSt initial viscosity (red), failing the SAE J306 requirements for SAE 90 gear lubricants. All other gear lubricants were within the required high-temperature viscosity range prior to the KRL Shear Stability Test.

Viscosity measurements following the KRL Shear Stability Test revealed that seven gear lubes sheared down below the minimum viscosity requirements (orange), failing the shear stability requirements of the SAE J306. The two gear lubes with the largest viscosity loss, as reflected in the following graph, were Royal Purple, losing 40.6% of its viscosity, and Torco SGO Synthetic, losing 35.2% of its viscosity. Royal Purple was the only gear lube to fail both the initial viscosity requirements
and the shear stability requirements. It started out too thick and ended up too thin.

Full test here: http://www.amsoil.com/lit/g2457.pdf

But I personally have seen the etching issues when RP gear lube was used in FC (2nd gen RX-7) transmissions and rear ends.

If your diff starts getting noisy I would replace the RP with Redline or Amsoil fast.

LionZoo

$20 a quart from somewhere. All for you guys' knowledge base right? And smoother shifting.

Icemark

Ah my local Ford dealers like to rip everyone off.

tunerwannab

iTrader: (1)

THe oil rep for my work explained this to us once and long story short if it calls for gl4 you should not use gl5. I cant remeber how he explained it so I will try to talk to him this week and report back the reasoning he provided.

tunerwannab

iTrader: (1)

API GL-4 and API GL-5 products typically use the same extreme pressure (EP) additive system, with the API GL-5 having about twice the concentration of a API GL-4. In service, these additives become active under extreme load and temperature when the protective oil film can be squeezed away. EP additives work by forming wear-resistant compounds with the metal of the gear tooth surface. As the gears mesh, these compounds shield the gear teeth from direct metal-to-metal contact that would cause wear and damage to the gears. If too little of the active additive is present, proper protection would be compromised. Too much of this additive could cause excessive chemical corrosion of the gear surface. If an API GL-5 gear oil is used in a application where API GL-4 gear oil is called for, chemical corrosion of "yellow metal" components may occur, such as bronze synchronizers, brass bushings, etc. This may lead to shifting difficulties or shortened equipment life.

newguy

great info^ Ive used redline MTL GL4 and liked it. Id like to run the 75w90 but its GL5 i believe.

So my question is does the RX8 tranny get hotter than 250*F internally during 100 degree summer days? I dont want to risk reaction to yellow metal above 250*. My center console like everyones gets pretty warm in summer.

rx8dad

Just bought some of the Motorcraft manual transmission oil.

http://www.fcsdchemicalsandlubricant...ission%20Fluid

It's a full synthetic GL-4, supposedly German made.

Hope it is as good as the Miata/Focus guys say it is.

Probably install it this weekend.

bsteimel

iTrader: (5)

Have you seen any tests like this with amsoil's gl-4 transmission gear lube? I put the severge gear in my diff and never had any complaints but it is gl-5 spec and don't want to put that in my tranny.