Safe to switch from SAE 80 to 75W-80?

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Since i bought my 94 Opel/Chevrolet (4 years ago) i am trying to decide which MTF to use. It has a manual transmission and it's front wheel drive.

The recommendation was SAE 80 as a "lifetime" fluid, and today there is pretty much only one option around here to choose from, which is a mineral oil and doesn't even mention the API rating (should be GL4), no OEM approvals.

cSt @ 100°C = 10,5

I had a good deal on some Total Traxium Gear 9 FE 75W-80 GL4 MTF, and been thinking about making the change this week, to replace a leaking gasket.

https://cdn.shopify.com/s/files/1/0...MISSION_GEAR_9_FE_75W-80_TDS.pdf?v=1625496725

I don't know a lot about transmission fluids, so i thought i should ask first, what do you guys think about the change?
 
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The viscosity itself is essentially the same, I wouldn’t bat an eye there. I think the area to watch to make sure the oil is correct for the synchro material, or you could end up eating the synchros quickly. Something about brass used in some vehicles? youre probably fine, I’ve swapped a lot of MTL before learning this and didn’t run in to trouble, but someone here might know a little better about that than me. Viscosity-wise, that’s good to go.
 
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You can use 75W-80 in place of SAE 80 without any issues.
Not sure about MT’s, but my understanding is that cold viscosity can be more important than hot viscosity for some differential applications due to the temperature at which they operate. Supposedly that is why Honda and Toyota have recommended SAE90 for above 0 temperatures.
 
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You can use 75W-80 in place of SAE 80 without any issues.

I'd agree under very most circumstances, but given the provided data is correct
going from 10,5 sSt down to 9,35 cSt is still thinner. This and perhaps hot climate
in Brasil would make me look for a 75W-85 GL-4. Unfortunately choice/availability
is much more limited. Maybe even look for a 75W-90 GL-4.
.
 
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A 1.15 cSt difference wouldn't concern me, especially since the quality is likely a bit better compared to 30 years ago.

There's certainly nothing wrong with going the 75W-85 or 75W-90 route either. RedLine MT-85 might be a good choice, but I don't know if that would be available down there.
 

LeoStrop

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I agree that the 75W-85 is a better choice, i regret that now. But the Total was a great deal and had to take it.

The most ideal product here should be the AC Delco 75W-85 GL4, which is recommended for later models, and i read somewhere the cSt was around 12. I didn't grab it because it was twice the price.

I thought the 75W-90 could be too thick, that's why i didn't considered using it.

But yes, temperatures here are very high and the car runs mostly above 3000 RPM in fifth.
 
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Yes you can use it. Total 75w80 usually are strong GL4, near or really unmarked GL4+ so protection should be good.
You can check Opel/GM and Fiat oils, here are 75w85 GL4 (GM 93165290 and Tutela Matrix).
 

LeoStrop

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I think i will skip the 75W-80, i have a friend that can use it in his Renault.

I am a bit afraid of going thinner, i live in a hot climate and sometimes push the car a little bit. Maybe my trans only reach 80°C/176F, and the difference there is around 3,2 cSt. ( the oils have a VI of 106 against 157)

Not sure how much that matter, but i will feel more comfortable using the 75W-85. Also because it needs to take the pan and replace the gasket to change the fluid on this car.
 

LeoStrop

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So, i sent the Total 75W-80 back, paid the difference and received the AC Delco 75W-85.

7585.jpg


On the bottle it says that it is imported from Germany and made by BP Europe SE Castrol.

The only Castrol 75W-85 made in Germany that i found was the Syntrans, so it should be similar to this:


Yesterday i made the change and all went well. The SAE 80 that was in there only had about 15K miles, but shifting definitely improved.

Hope the new gasket + a little bit of silicone will not give me any leaks this time.

Thanks all.
 

FCD

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I asked this same question a few years ago here, both my 1975 Ford Capri and 1988 Ford Escort spec SAE 80 for the gearbox, i ended up putting the recomended SAE 80 in both, but since it is getting harder and harder to find i might use 75W-80 the next time, or 75W-85.
 
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So, i sent the Total 75W-80 back, paid the difference and received the AC Delco 75W-85.

On the bottle it says that it is imported from Germany and made by BP Europe SE Castrol.

The only Castrol 75W-85 made in Germany that i found was the Syntrans, so it should be similar to this:


Yesterday i made the change and all went well. The SAE 80 that was in there only had about 15K miles, but shifting definitely improved.

Hope the new gasket + a little bit of silicone will not give me any leaks this time.

Thanks all.

Well interesting.
From my data it's not Syntrans, it's Castrol 75w85 for GM family (high quality group III) true GL4 (Castrol BOT 402, Opel 93165290, Saab MTF063 etc). Good move.
 

LeoStrop

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I asked this same question a few years ago here, both my 1975 Ford Capri and 1988 Ford Escort spec SAE 80 for the gearbox, i ended up putting the recomended SAE 80 in both, but since it is getting harder and harder to find i might use 75W-80 the next time, or 75W-85.

I saw that when i was searching for some threads of this subject, i was going to ask you what you ended up using.

From what i saw, most SAE 80 and "80W" GL-4 have a [email protected] around 10~10,9, the 75W-80's around 8.9~9,5 and 75W-85's around 11~13.

So for our oldies, the 75W-85 will give us a little less drag in cold temperatures and a little bit of extra protection at high temps. I did not considered Motul because it was both GL-4 and 5, but maybe Total has a good option around there?

Well interesting.
From my data it's not Syntrans, it's Castrol 75w85 for GM family (high quality group III) true GL4 (Castrol BOT 402, Opel 93165290, Saab MTF063 etc). Good move.

Well that makes even more sense!


Looking at this old TDS , it meets Opel B 040 2071 and GL-4, both are also behind the bottle of the AC Delco, and also red colour.

Thanks for the info!
 
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So, i sent the Total 75W-80 back, paid the difference and received the AC Delco 75W-85.

View attachment 96615

On the bottle it says that it is imported from Germany and made by BP Europe SE Castrol.

The only Castrol 75W-85 made in Germany that i found was the Syntrans, so it should be similar to this:


Yesterday i made the change and all went well. The SAE 80 that was in there only had about 15K miles, but shifting definitely improved.


Glad to see everything went well while interesting to see this AC Delco made
by BP/Castrol Germany is sold in 1 Liter bottles. Oddly enough Castrol Transmax
Manual Long Life 75W-85 GL-4 (formerly Castrol Syntrans 75W-85) is available
in Europe in 20 Liter jugs and up only. Guess why I don't use it. That said Castrol
recommends using it in commercial trucks and busses.
Same or not - I'm convinced Castrol/BP makes excellent transmission fluids. I do
use them wherever possible.
.
Castrol Transmax Manual Long Life 75W-85 GL-4  9 2020.jpg
 
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FCD

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If it wasn't so expensive i would get some Redline MTL 75W-80, it even states on the website it is recommended as a replacement for SAE 80, with the Monograde 80 it's true that the shifting is a little notchy when cold, but perfect once the oil has warmed up a bit.
 
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If it wasn't so expensive i would get some Redline MTL 75W-80, it even states on the website it is recommended as a replacement for SAE 80, with the Monograde 80 it's true that the shifting is a little notchy when cold, but perfect once the oil has warmed up a bit.
How much is over there in Spain?
 

FCD

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Glad to see everything went well while interesting to see this AC Delco made
by BP/Castrol Germany is sold in 1 Liter bottles. Oddly enough Castrol Transmax
Manual Long Life 75W-85 GL-4 (formerly Castrol Syntrans 75W-85) is available
in Europe in 20 Liter jugs and up only. Guess why I don't use it. That said Castrol
recommends using it in commercial trucks and busses.
Same or not - I'm convinced Castrol/BP makes excellent transmission fluids. I do
use them wherever possible.
.
View attachment 96641
I also am a fan of Castrol's gear oils.
Mannol however does make a Synthetic Blend 75W-85 that is GL-4 and is sold in 5 Liter jugs, and it's very well priced.
 
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