Best tranmission oil?
 

2005 Nissan 350z Enthusiast --- First time changing the transmission oil, possibly since the car was made (not sure about previous owners work done on the vehicle)

I want to know the best tranmission oil to use?
I am seeing a lot of reviews about mixing 50/50 Redline MTL with MT-90.
I understand that at the end of the day it is all preference, but I do not know much about tranmission oils or transmissions PERIOD.

Presuming you're referring to a 6MT.

Redline MT-85 (undiluted) is arguably the best fluid BECAUSE it is pretty much the only thing out there that has the proper blending of friction modifiers (additive to the GL-4 spec fluid to make it "not so slick") required of the Nissan transmission. Use the recommended 75w-85

You also cannot go wrong with the OEM fluid, also in 75w-85.

Shop I use used to use MT-85 exclusively but now they're back to Nissan fluids.

I guarantee others will swear by what they use, Royal Purple, Motul, etc. but I've run MT-85 in all my cars with transmissions ranging from CD001, 008, 009. All run great with Redline.

MTL blended with MT90 is essentially MT85. I run MT85 in both my street and race Z and swear by it. Nuff said.

I run Redline MT90 and I have some hard / slow shifts in my higher (4th / 5th / 6th) gears ... next time I swap trans fluid I'll be doing what DK said and running MT85.

I've just stuck with the Nissan OE fluid in my MT. I do like Amsoil in the diff though. You might as well change both fluids while you're under there.

Service manual only specifies intervals for inspection of these fluids, my car is low mileage but 10 years old at this point, is there a recommended mileage/years when this should be done?

If it's never been done before, you should just change it out as preventative maintenance after 10 years.

I used "Mobil 1 Delvac Syn Gear 75w-90" for the last change in my CD009 equipped G sedan, and I like it better than OE fluid and regular M1 75w-90 synthetic in cold (<40°F) conditions. Once up to temp, I can't tell the difference between the 3.

Sorry to say, the Mobil 1 Delvac Syn Gear 75-90W oil is a GL-5 rated lubricant. It's intended for use in non-synchronized gearboxes, diffs and final drives. The beautifully built 6-speed in your Z is specifically rated to use a GL-4 lubricant. The pressure sensitive compounds included in the Delvac gear oil will degrade and damage the soft metals (like brass) in your Z's syncros.

Don't believe me? Read it on Mobil's own website: https://www.mobil.com/english-gb/com...gear-oil-75w90

Good to know.. I guess I'm due for another fluid change! Fortunately I've only been running it for ~2500 miles.

EDIT: This paper does a pretty good job explaining why I done fudged up: 'When we use a GL-5 product in a transmission that requires GL-4, we normally find 2 to 4 times as much copper in the used oil as we would with a GL-4 product."

Always been Nissan OEM fluid for me. Went 75kmi on my CD008 before replacing it a few months ago, about 30k of those are track miles...

Oh, and brutally honest confession...didnt change the transmission fluid once.