GL4 MT synthetic transmission fluid for Forte Coupe 6 speed. Can i use GL5? + other questions.

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I've been thinking since another user posted and informed me on, that i might of bought the wrong mt fluid for the kia. It is Full Synthetic Valvoline 75W90 gear oil but i believe it is GL5, and not GL4, and to be honest I know very little about MT fluids - but i'm learning fast!.
The plan was to change the current fluid out with the Valvoline 75W90 run for some time, then drain and refill with Amsoil Manual Transmission & Transaxle Gear Lube 75W-90. But if the Valvoline is GL5, (is it backwards compatible with GL4?) or should i skip the pre change, and just go right to Amsoil GL4 Synthetic MT fluid:

Backstory is i called the dealer looking for OEM 75W90 fluid, and they told me they dont sell it by the qt, they only have a 55 gal drum type deal, and to go to autostore and pick up any 75W90 and it will be good to go so i did that not understanding anything regarding GL4/GL5, or anything else about the MT fluid.. Can any one shed some light? Should i return the Valvoline, and just do one change of the MT fluid to Amsoil - then call it good? Its about 23$ a qt, but its not like im changing it out every 5-10K miles. I'd have to order it online, and have it shipped. It seems like all the kia forums highly recommend this fluid for the six speed manual transmission, but i've never personally used Amsoil before... in anything.
I am not trying to correct any issues, no pop outs, grinds, or abnormal notchy-ness, i'm just looking for optimum protection, and to have the MT feel as good as it can get it.

So my questions, is there a fluid locally that I can just pick up and use that is full synthetic and GL4 compatible?
Whats the OCI on a MT fluid? It feels pretty good currently, so im assuming its been replaced in past, with what im not sure. Kia might tell you never to change it, you know "fluid for life" type deal, but it does have drain plug with magnet, and fill port that you put in about 1.9 qts of fluid.
Stick with GL4 Amsoil Synthetic, or would another GL4 synthetic 75W90 work from auto store?

Thanks for all your feedback and suggestions - it never goes unnoticed, i know as one member said im "all over the map" and there is a little truth to that. I try to stay on track, think straight and logical, but sometimes my OCD kicks in to the max, and i just cant lol, and what seems insane to some of you, (like to give the mt a change of fluid before putting in the good fluid thus in turn changing it twice) and things like that. I am working on it.... honestly.. :) Thanks!. 🙏
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I would skip the pre-change with the GL-5 and put in the GL-4 lube if that's what is recommended. Just go with a GL4 synthetic 75W90 from your auto store. I wouldn't waste the money on an OEM lube or any Amsoil product. Save the GL-5 stuff for a differential. The LSD additives likely will cause issues with your transmission.
 
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dnewton3

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My MX-5 has the same spec; GL-4 75w-90 for the 6-spd manual.

Do not use the typical GL-5 gear oil. Get the GL-4 specifically made for MT applications. None of the choices will be "cheap", but the OCIs can be fairly long (anywhere from 50-100k depending upon shearing loads from your driving style), so the OCI cost is spread across several years.

Here's a list of fluids that you might consider. Many of these would be available at a local dealer or auto-parts if they "order" it for you.
Ford: https://www.fcsdchemicalsandlubricants.com/Products/Details?cid=120&pid=239
Mazda: (can't find the link, but it's their MT GL-4 fluid at the dealer parts counter)
Amsoil: https://www.amsoil.com/p/manual-transmission-transaxle-gear-lube-75w-90-mtg/?code=MTGPK-EA
Red Line: https://www.redlineoil.com/mt-90-75w90-gl-4-gear-oil

The RL is the product I chose because of price and availability from Amazon, but any of those would do nicely.

You don't need to do a "flush" cycle on a small manual trans. Just drain out the oil, fill with the new, and drive it another 50k or more. All these syn fluids listed above are excellent products and will last a long time in service. There's no combustion byproducts in the manual trans fluid like an engine, so a flush isn't necessary. Just draining the oil fluid out when warm will carry out the bulk of the break-in metals in the OEM fluid.
 
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1 SX

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You shouldn't use a GL 5 in a manual transmission.

Go with a GL 4. But something like the Redline MT-90 would work. (75w90).
Now that i see it in text, it looks funny (and apparently wrong) maybe i should be looking for redline and not amsoil. I dont know where i got amsoil from, but the kia forums are mentioning REDLINE, not AMSOIL...

Where can i pick up redline? Is this online only order or would a local napa or something carry it? MT-85/MT-90 would be perfect.
 

dnewton3

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If your application will be difficult to get the fluid in due to space considerations, the Amsoil has that nice flexible packaging which makes getting into tight spaces very easy.

I have a little manual pump that installs on the bottle threads, so I just used the Red Line with my car on a lift.

Again, the RL is easy to get right off Amazon. Just make sure to get the right one; see my post above.


If space considerations are important, I'd pay for the Amsoil because of the packaging with the collapsible container.
If not, then I'd get the RL (which is what I did) due to being about $4/qrt less money. Amazon has a 2-pack of the MT-90 for $37, which also qualifies for free shipping to your door. Doesn't get much easier than that.
 
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1 SX

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Might be in luck with O'Reilly, they have the MT-85 for Hyundai/Kia and a couple others. Its GL4 and full synthetic, 20 bucks a bottle - two needed. Not to shabby. There is a local O'Reilly near me, i'll call and see if they have any in stock, website says they do.
MT-85 75W-85 GL-4; Gear Oil; 1 Quart; Fully-Synthetic; Manual Transmission; MT-85 75W85 GL-4 - fully-synthetic, ester based for manual trans and transaxles, safe for brass, balanced friction for improved gear and synchro life, better cold shifting, for Nissan, Mitsubishi, Hyundai, Kia, NV4500

If out of stock, i'll have them order it, or Amazon it. Im in no rush to change out fluid, just want to do it for piece of mind.
 
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Usually Advanced Auto Parts and O Reiley's sell it., or you can order if of their website or FCP Euro. Redline and Amsoil are fine. But do you need a 75w85 or a 75w90? I would put your car into both Redline and Amsoil product lookup page and see what they say.
 

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Usually Advanced Auto Parts and O Reiley's sell it., or you can order if of their website or FCP Euro. Redline and Amsoil are fine. But do you need a 75w85 or a 75w90? I would put your car into both Redline and Amsoil product lookup page and see what they say.
I think the factory spec is 75W85 but 75W90 would work. . Amsoil says 75W90, Redline says 75W85.

I'd like to stick to as close as possible to the factory spec fluid so i will most likely order the 75W85 redline, and skip everything else. Change it once, and de done with it.
 

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Ok, i am very happy i did not use the wrong fluid, so thank you for noticing that. I ordered the correct Redline 75W85 GL4 full synthetic MT fluid from O'Reileys 2 QTS. its in the hub, will be delivered to store today by 1PM today.. I won't get around to changing it today, but will this week.. Will update if anything pops up, but this should be easy drain and fill, and good to go.. Thank you for guiding me to the correct fluid, it was only $43 bucks after tax. Seems reasonable to me.
 
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I used the same redline fluid in the mazda 6 speed. Worked well even at -30 and colder this winter.
 
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Ok, i am very happy i did not use the wrong fluid, so thank you for noticing that. I ordered the correct Redline 75W85 GL4 full synthetic MT fluid from O'Reileys 2 QTS. its in the hub, will be delivered to store today by 1PM today.. I won't get around to changing it today, but will this week.. Will update if anything pops up, but this should be easy drain and fill, and good to go.. Thank you for guiding me to the correct fluid, it was only $43 bucks after tax. Seems reasonable to me.
Sounds good! Don't forget to update us, even on the good results
 
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Backstory is i called the dealer looking for OEM 75W90 fluid,

So you're saying OE fluid is 75W-90.


So my questions, is there a fluid locally that I can just pick up and use that is full synthetic and GL4 compatible?

No, it isn't 'backwards compatible'. API GL-5 is for different applications, e.g. differentials
on RWD cars and trucks. It is rarely used in manual transmissions using synchronizers and
likely will led to poor shifting.


I think the factory spec is 75W85 but 75W90 would work. . Amsoil says 75W90, Redline says 75W85.

So it's 75W-90 now? Wouldn't it be better to first determine the OE fluid's specs first?
Perhaps there's a UOA or even better a VOA of this OE MTF to be found on this forum.
Most of the time it isn't a good idea to go thicker without any requirement to do so.
Thicker MTF will also tend to make shifting worse when cold. A typical 75W-90 is almost
always thicker compared to a 75W-85 and more so compared to a 75W-80 or even 75W.


I'd like to stick to as close as possible to the factory spec fluid ...

I too would recommend to retain the OE specs. This is a small FWD car with a transverse
mounted engine, true? The vast majority of these need a thin (75W or so) GL-4 MTF. The
Valvoline isn't even a MTF and it seemingly also doesn't say GL-4.


I ordered the correct Redline 75W85 GL4 full synthetic MT fluid from O'Reileys 2 QTS. its in the hub, will be delivered to store today by 1PM today.

You're quick, perhaps too quick. I'm under the impression it isn't even 100 % clear what
spec the OE fluid is. There's so much helpful information on the forum. Why don't you
spend some time to read it?
.
 

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So you're saying OE fluid is 75W-90.




No, it isn't 'backwards compatible'. API GL-5 is for different applications, e.g. differentials
on RWD cars and trucks. It is rarely used in manual transmissions using synchronizers and
likely will led to poor shifting.




So it's 75W-90 now? Wouldn't it be better to first determine the OE fluid's specs first?
Perhaps there's a UOA or even better a VOA of this OE MTF to be found on this forum.
Most of the time it isn't a good idea to go thicker without any requirement to do so.
Thicker MTF will also tend to make shifting worse when cold. A typical 75W-90 is almost
always thicker compared to a 75W-85 and more so compared to a 75W-80 or even 75W.




I too would recommend to retain the OE specs. This is a small FWD car with a transverse
mounted engine, true? The vast majority of these need a thin (75W or so) GL-4 MTF. The
Valvoline isn't even a MTF and it seemingly also doesn't say GL-4.




You're quick, perhaps too quick. I'm under the impression it isn't even 100 % clear what
spec the OE fluid is. There's so much helpful information on the forum. Why don't you
spend some time to read it?
.
So the dealer told me 75W90 is "compatible" for this car and what they use for MT fluid changes, its in the 55 gal drum though, and they cant sell me any. I did not at the time pick up on the word "compatible"

The OEM correct factory spec is 75W85 in GL-4. Filled for life. about 2 QTS.

I will try to stick with the factory spec, and rating, now that i know what it is with more research/reading on these and multiple different forums. (I did research, and found answer- thanks!. I would of been in trouble if i listened to the dealer, with out more research, and just dumped in GL-5 75W90. I also made the mistake by assuming 75W90 was the correct fluid, and never thought about the actual underline spec or anything else... I simply did not know, and was going off what the dealer told me. "Yeah go to any parts store pick up 75W90 and change it out" - But now i know, and am very thankful for the info :-D

Im not looking for "compatible", im looking for as close to OEM spec as possible, but with synthetic properties.

I now dont trust the dealer when it comes to fluid changes such as automatic and manual fluids changes if they are using "compatible" and not OEM spec fluids. I was naïve to think otherwise I guess.
IMHO big difference there.
 
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dnewton3

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Regarding the choice between 75w-85 and 75w-90 for this application, you will never know the difference when driving. And the trans isn't going to know the difference in terms of wear. Don't sweat such minor details; you'll only needlessly frustrate yourself.
 

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The Kia and Hyundai spec from the factory for the 6 speed manual transmission was 75w85 GL-4 (Red Line MT-85) but a few years ago they changed it to 70w GL-4 (Redline MT-LV 70w/75w), even for older models. This is what I bought for my 19’ Soul.

You’re fine using the Redline 75W85 GL4 you just ordered. But do not use GL-5 in your manual transmission.
Thanks!, I will not use GL-5. The wrong GL-5 Valvoline 75W90 will be returned, and i will use the closer oem spec redline 75W85 GL-4. Will update with any improvements or anything else that I notice, but alot of kia/hyundai people are using this redline fulid with zero complaints, and most even noticed an improvement in all weather shifting, and smoother "feel".

I did not know about Hyundai changing the spec/weight, but its not the first i've heard of a car company changing a spec years after release.
 
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Rock Auto used to have a Valvoline MTF that is actually suitable for your manual transmission (called Valvoline Professional Series or VPS), but they don't have it in stock. Part number 508216. It is primarily only sold to shops and available at VIOC quicky lubes. Maybe you can find another place that will sell it to retail customers :unsure:

Otherwise, the only 75w90 GL4 usable in a manual transmission you'll find on the shelf of a US store is Liqui-Moly 20012 at Napa.
 
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