About GL4 and GL5 gear oil

[baomo]

I've been doing maintenance work on my '02 Kia recently and noticed a leak in the transfer case. I can't tell yet if it's a seal or is just seeping from somewhere. Doesn't get a lot of miles so I'm going to top it off an keep and eye on it and see how much it leaks.
The manual specifically calls for 75W90 GL4 for the transfer case (and GL5 for the differentials) so I assume there is yellow metal or something in there. Most gear oils I'm seeing are GL5. I saw Redline and Royal Purple make GL4 but I'd rather not put a $20/quart fluid in there just to have it leak out in a week and on the other hand if I top it off and it doesn't leak badly I may leave it in there for a while so I don't want something corrosive in there.

Is there an easily found affordable GL4 gear oil? I see Valvoline for around $6 advertised as GL4/5 for differentials and GL5 for 'nonsyncro tranny' which I take to mean not really yellow metal safe. Or am I understanding that wrong?

 

[drtyler]

Napa and Amazon sell GL4 rated Sta Lube 85W90.

I would just use one of the dual rated GL4/GL5 oils.

 

[MolaKule]

What is the maintenance history? I.e., is this the factory fill or has it been replaced since '02 and with what fluid?

You have to determine if the leak is caused by a Gasket or a rotating component Seal.

A drain and refill with say synthetic Mobil 1 75W90 or Redline MT-90 could possibly (no guarantee) swell a rotating component seal.

The most likely reason for specifying a GL-4 rating is that the loads within the TC are not as high as the loads encountered in a hypoid differential and has nothing to do with copper alloy components.

 

[d00df00d]

Originally Posted By: MolaKule
The most likely reason for specifying a GL-4 rating is that the loads within the TC are not as high as the loads encountered in a hypoid differential and has nothing to do with copper alloy components.


Interesting.

Isn't it true that GL-4 fluids tend to be nicer to copper than GL-5 fluids, at least per ASTM D130 (ratings of 1A vs. 1B, respectively)?

 

[baomo]

I think it's the original fill but can't be 100% certain, it only has around 65k miles. I can't quite tell if the leak is coming from a seal or gasket, that why I want to top it off and monitor it.

So it has nothing to do with metal corrosion, in that case any GL5 would be suitable?

 

[MolaKule]

Originally Posted By: d00df00d

Interesting.

Isn't it true that GL-4 fluids tend to be nicer to copper than GL-5 fluids, at least per ASTM D130 (ratings of 1A vs. 1B, respectively)?


In most Transfer Cases, the power transfer components and bearings are steel alloys with aluminum cases.

In the past GL-4 fluids simply contained lower levels of active S-P EP additive that were also used at higher levels in GL-5 fluids and the S-P additive was unbuffered.

Today's EP additives contain lower levels of sulfur and are buffered. In fact, many formulations today contain mostly multi-functional phosphate additives with a little ZDDP, hence the low sulfur content.

 

[MolaKule]

Originally Posted By: baomo
I think it's the original fill but can't be 100% certain, it only has around 65k miles. I can't quite tell if the leak is coming from a seal or gasket, that why I want to top it off and monitor it.

So it has nothing to do with metal corrosion, in that case any GL5 would be suitable?


You could, but for reasons of economy, the StaLube 80W90 would also be a good choice until you find the leak.

IN my experience, the clamshell gasket is usually not at fault, but rather it is one of the shaft seals that has worn.

 

[spasm3]

.

 

[JustN89]

Originally Posted By: MolaKule
What is the maintenance history? I.e., is this the factory fill or has it been replaced since '02 and with what fluid?

You have to determine if the leak is caused by a Gasket or a rotating component Seal.

A drain and refill with say synthetic Mobil 1 75W90 or Redline MT-90 could possibly (no guarantee) swell a rotating component seal.

The most likely reason for specifying a GL-4 rating is that the loads within the TC are not as high as the loads encountered in a hypoid differential and has nothing to do with copper alloy components.


Glad to see you posting again, Mola.

 

[baomo]

Originally Posted By: MolaKule
Originally Posted By: baomo
I think it's the original fill but can't be 100% certain, it only has around 65k miles. I can't quite tell if the leak is coming from a seal or gasket, that why I want to top it off and monitor it.

So it has nothing to do with metal corrosion, in that case any GL5 would be suitable?


You could, but for reasons of economy, the StaLube 80W90 would also be a good choice until you find the leak.

IN my experience, the clamshell gasket is usually not at fault, but rather it is one of the shaft seals that has worn.

I suppose the 85w90 being thicker than the called for 75w90 could slow the leak if it turns out to be just a gasket seep.
For arguments sake once do I get the source of the leak taken care of, you're suggesting I can refill with GL5? Is the low sulfur buffered GL5 you're referring to the MT-1 spec?

 

[MolaKule]

Both of the oils you reference are SAE 90 grades so should have very similar viscosities.

Here is what I would try to do. Find an exploded view of your Transfer Case and determine for sure there are NO brass bearings or brass clutch components before going to a GL-5 rated lubricant.

My Frontier uses a GL-5 rated 75W90 but I know for sure its components contains only steel alloys.

 

[baomo]

Thanks for the help. I checked a repair manual that has a tear down of the transfer case. It doesn't say whether the sycro is steel or brass but does mention a bronze plug inside. But I guess that's considered a red metal. Confusing the matter further it simply recommends a 90W gear oil without mention of a GL spec.
I'll top it off this weekend with the Sta-Lube 85W90 from Napa, for $11. When I track down and fix the leak I'll refill with either GL4 Redline or RP to be safe (it only takes 1.8qt) unless I find a reason to do otherwise.