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

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I'd largley ignore the API rating and just look specifically for a manual transmission fluid in the viscosity you require. Some MTF's are indeed GL-5 rated lubes and can be used perfectly well in a manual transmission.
 

MolaKule

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...Some MTF's are indeed GL-5 rated lubes and can be used perfectly well in a manual transmission....
Some, but few are and usually for special applications such as common sump transaxles and HD trucks.

GL-5 fluids have a different chemistry and base oil mix than do GL-4 MTF's.

Don't assume because they are both "gear" oils that one can be substituted for another.

Most vehicles and light duty trucks with MT's specify GL-4 MTF's.

If in doubt, take a sample, have it analyzed, and post it here on BITOG so we can attempt to match it up.

 
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1 SX

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To update on this. Changed out the engine oil, and transmission fluid today. For the engine oil i used 5W30 valvoline synthetic with a OEM Hyundai filter - and it took all 5 qts, not 4.5 (and even still its only at 85% full.) But i let it drain for 1.5 hours, and the sonata is the same way, takes about 5.6 qts on a 1-2 hr drain.

I used the OEM spec GL-4 Synthetic RedLine 75W85 fluid that is Hyundai & Kia approved in the manual transmission and it really does feel better. It was not bad to begin with but I just think the fluid it was old, and slightly deteriorated so it was affecting the shift "feel". It now no exaggeration glides into any gear at any RPM. The is also no transmission gear noise, and no grinds. I'd call this a success.. Pictures for enjoyment
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MolaKule

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I used the OEM spec GL-4 Synthetic RedLine 75W85 fluid that is Hyundai & Kia approved in the manual transmission and it really does feel better.
I am not sure that RedLine 75W85 is Hyundai & Kia approved, or that Redline has approvals by them.

Your choice of viscosity may be correct, but approvals?

So if it shifts better that is good.
 

1 SX

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I am not sure that RedLine 75W85 is Hyundai & Kia approved, or that Redline has approvals by them.

Your choice of viscosity may be correct, but approvals?

So if it shifts better that is good.
okay its "recommended" for Hyundai kia, and a few others. My wording was off. I should of said recommended.....
Redline .jpg
 
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Some, but few are and usually for special applications such as common sump transaxles and HD trucks.

GL-5 fluids have a different chemistry and base oil mix than do GL-4 MTF's.

Don't assume because they are both "gear" oils that one can be substituted for another.

Most vehicles and light duty trucks with MT's specify GL-4 MTF's.

If in doubt, take a sample, have it analyzed, and post it here on BITOG so we can attempt to match it up.


That's why I was quite specific that it had to be an MTF.

I use Fuchs Sintofluid 75w80 as a universal oil for most manual gearboxes. It's a GL-5 lube despite being an MTF.

 
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MolaKule

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That's why I was quite specific that it had to be an MTF.

I use Fuchs Sintofluid 75w80 as a universal oil for most manual gearboxes. It's a GL-5 lube despite being an MTF.

What is the 40C and 100C Kinematic Viscosity of this fluid in cSt.? 75W80 tells us nothing but the 'range' of possible viscosity.

 
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MolaKule, could you explain your comment, a bit more please (post # 24, above)? Are you suggesting that the nominal SAE rating, e.g. in this case 75W-85, represents a range of viscosities and that a Mfr may want more specificity than just a range? Also, would a Mfr want to know an oil's chemistry or friction properties or Brookfield (is that Dynamic- ?) viscosity too? Just how important is a Mfr's approval if the oil meets the nominal SAE rating?

TIA
 

Job

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I saw this gear oil, and it is GL 5 but also ok for synchronized transmissions. When they say it specifically, I trust it. My vehicle states GL 4 or 5 so I am safe, but I wanted to be safer. Plus it wasn't expensive with Napa coupon, like $11 something. Interested to learn more about it. It seems they claim better quality base oil and less ep additive as the reason.
 

MolaKule

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Here's the problem as I have pointed out in many posts about the SAE grades. The 7XWYY tells you nothing about the actual viscosities at 40C and at 100C. You have to go to the Oil properties Product Data Sheet to see what the actual viscosities are or have it tested. I consider the 100C very important as this is the viscosity at which the minimum film thickness is present.

An approval simply means the fluid has been tested, the results given to the OEM, and the OEM has stamped it as qualifying for a specific application, and put on their approval list.

If the required tests by the Blender showed the tests passed according to the OEM's testing protocols, then no specific chemical information about the MTF is needed by the OEM.

This is why I have commented many times that one should pull a sample of the OEM fluid and have it analyzed and then post it on BITOG so we can attempt to match it up with a third party fluid.
 

Job

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Which vehicle? I wouldn't use this oil in any synchronized transmission.
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Are you referring to the Eneos? They say very definitely it is ok. It’s in the link. Made in USA. My vehicle,Toyota T100 with W59 trans says use gl4 or gl5. But I decided this is safer than one that says gl4 alone, as it specifically states compatibility in writing. Since I saw Valvoline says gl4 but also not for synchromesh, I said wait a minute here.
 
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Are you referring to the Eneos? They say very definitely it is ok. It’s in the link. Made in USA. My vehicle,Toyota T100 with W59 trans says use gl4 or gl5. But I decided this is safer than one that says gl4 alone, as it specifically states compatibility in writing. Since I saw Valvoline says gl4 but also not for synchromesh, I said wait a minute here.
Is yours a hypoid transmission?
 
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Are you referring to the Eneos? They say very definitely it is ok. It’s in the link. Made in USA. My vehicle,Toyota T100 with W59 trans says use gl4 or gl5. But I decided this is safer than one that says gl4 alone, as it specifically states compatibility in writing. Since I saw Valvoline says gl4 but also not for synchromesh, I said wait a minute here.

Yes, I refered to the Eneos. Just being 'ok' doesn't sound like a perfect match to my ears.
They don't mention 'suitable for W59 transmissions' or similar. That would be 'definitely'.
I don't get why you think GL-4 AND GL-5 simultaneously would be anything superior in
your longitudinal manual transmission as it most definitely doesn't use any hypoid gears
at all (unlike your rear diff). I have abolutely no experience with this W59 transmission, so
take this with a grain of salt, but in the vast majority of similar cases a GL-4 only MTF is the
most appropriate fluid. I think waiting a minute was a good idea.
 

Job

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Yes, I refered to the Eneos. Just being 'ok' doesn't sound like a perfect match to my ears.
They don't mention 'suitable for W59 transmissions' or similar. That would be 'definitely'.
I don't get why you think GL-4 AND GL-5 simultaneously would be anything superior in
your longitudinal manual transmission as it most definitely doesn't use any hypoid gears
at all (unlike your rear diff). I have abolutely no experience with this W59 transmission, so
take this with a grain of salt, but in the vast majority of similar cases a GL-4 only MTF is the
most appropriate fluid. I think waiting a minute was a good idea.
Did you read what the bottle says? compatible with synchromesh , and further enables easy and smooth shifting in low temps. Do you think they are talking about easy and smooth rear axle gear shifting?
"OK" is my description, for me. Many kinds of "ok". It isn't something to say, OK doesn't sound good enough.
 
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I've read the entire product description. Bottle says 'LSD gear oil' and
'LSD, GL-5' on front. I'd say this makes me pondering, to say the least.
I'm sure I'm not a person who comments inconsiderately on a subject.
I'd suggest to compare this product data sheet to others to get a feel
about the differences in the wordings.
.
 

Job

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I've read the entire product description. Bottle says 'LSD gear oil' and
'LSD, GL-5' on front. I'd say this makes me pondering, to say the least.
I'm sure I'm not a person who comments inconsiderately on a subject.
I'd suggest to compare this product data sheet to others to get a feel
about the differences in the wordings.
.
The back of the bottle says compatible with synchromesh. This takes away the yellow metal worries. Then it says our proprietary tech enables easy shifting. That’s my end of specificity needs.
Whatever company, if they are reputable and say compatible with synchromesh, and GL4 or 5, on my vehicle it is OK. What bothered me was Valvoline and others putting GL4 and for non sychronized on the bottles. So if Fly By Night Oil says GL4, but nothing else, it does meet GL4, but is it compatible with synchromesh? They only have to say GL4.
I just thought people might be interested in a GL5 that also works for manual transmissions. It definitely shifts like a champ now. But I did make some repairs to poor work on the shift lever area. The shift lever seat and nylon ball on the shift lever end were gone, not there. $8 worth of oe parts and they are back in again. So easy to do too.
 
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Dude, I've seen all of that, no need to repeat it again and again.
This product obviously is still marketed primarily as a 'GL-5 LSD
gear oil intended for rear differentials'.
If you made your choice before asking here just use it. However
you won't convince me it's a wise choice for longitudinal manual
transmission applications like yours.
.
 
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I would add that manual transaxle use in most cases would have identical considerations to (mostly rear wheel drive) longitudinal manual transmission considerations vis à vis GL-4... meaning most transaxles have (only) helically-cut gears, i.e. no ring and pinion arrangements. So they too do not warrant high EP formulations, and instead warrant GL-4 lubricant use only (for best synchromesh unit care).
 
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