Redline MT-LV 70W/75W gear oil for 5 speed manual Mirage (OE is 75W80)
 

I was poking around today looking at different gear oils. The 2014+ Mirage calls for a 75W80 gear oil. The 75W is the engine viscosity when cold, and the 80 is the viscosity when its hot. All oil is substantially thicker when cold, so getting a low first number is a good thing as it will always be thinner when hot. You just don't want it to get too thin, or you can accelerate wear in your transmission. Here is a chart to help illustrate things.

https://mirageforum.com/forum/attach...0&d=1543607872



Therefore, I was looking to see if I could get a 70W80 or even 65W80. Alas, I can not find anything like that. However, what I did find was Redline MT-LV 70W/75W. You'll notice this doesn't follow the normal naming convention. So, I'm not exactly sure what to think about it. It is quite a bit thinner than Redline MTL 75W80 that many here have used.

https://mirageforum.com/forum/attach...1&d=1543608490

Here are the viscosity specs of the two:

75W/80 (OE spec)
Vis @ 100°C, CSt 10.2
Vis @ 40°C, CSt 50

70W/75W
Vis @ 100°C, CSt 6.5
Vis @ 40°C, CSt 9.8


For reference, 40C is 104F. That already seems warm for a manual transmission, but I haven't measured my transmission's temperature. Anyway, at 104F, you can see the 70W/75W is 5 times thinner than the 75W80 oil. Thats a heck of a lot less churning going on. Less churning means more power and efficiency.

Anyways, I post this info because I am thinking about using it in the Mirage. I have contacted Blackstone Labs, a third party oil analysis company. I've asked them how they recommend I proceed with testing this oil with minimal risk to my transmission. I've used them many times in the past for engine oil analysis and they're very helpful.

104 I can still touch. My Zf6 in the 250 gets too hot to touch, more like coolant temps or above.

All the manual transmissions I have worked on with in the last 20 to 25 years all had ATF in them or special synchro manual transmission fluid (a GM thing) that looks, feels, smells and tastes a lot like ATF.

My leaf even uses ATF.

I got a reply from Blackstone Labs.


He didn't tell me I'm crazy or anything, so I think I am going to source the gear oil and find a time to put it in.

I got another reply from Blackstone Labs. I had asked them if they had wanted to do a virgin oil analysis on the MT-LV fluid. They said no, unless I wanted it for reference. Just send in the oil at 5k miles.

Naming convention
 

The T56 in the Viper used 75W/85W. I remember very specifically because there was an extended forum thread asking about alternatives, and our resident fluids guru, an oil formulator for Texaco, said the second W isn't a typo and there was something different about oils marked as such (but I can't for the life of me remember what the actual differences are).

I ordered two quarts of Redline MT-LV gear oil for my 2014 Mirage. It was a bit pricey at $42 shipped. I ended up ordering it from ebay. I had a real hard time finding it anywhere else than Redline's own site. The priced shipped from them was only a few dollars more. But, all the distributors on their site didn't even carry it. In any case, I am looking forward to trying it out.

Nice. I tried sourcing that oil locally and gave up.

I'm not surprised at all. I think its pretty new and nobody has it. No OEMs are really speccing it yet, so its probably not selling well yet.

Bit off topic...but why do they rate the thickness of engine oil different from the manual trans oil? I'd have assumed, based on the numbers, that 75w is a heck of a lot thicker than 10w.