What is best transmission oil?

[nightheron]

What do you think is the best gear oil for the 240sx with a manual transmission. I've been using Red Line MT-90 , but it seems too thin. Any input would be good.
Thanks

[waxdnuggz]

Amsoil gl4 synthetic gear oil. Cannot go wrong. I have always used that in my 240s and I love it it has eliminated 1st gear grinds and reverse problems. Ill never use anything else

[2_Liter_Turbo]

^^^ Great Oil, but if you're on a tighter budget (some people are), then make sure you get a GL4 certified oil. If it's GL5 it contains chemicals that will eat away at the synchros. It can be both GL5 and GL4, but not GL5 alone. Amsoil makes great stuff though, so if you can swing it, it's definitely a good choice.

[nightheron]

What do you think of the Red LIne MT-90 GL4?

[waxdnuggz]

I personally do not like redline. I feel its very thin. Amsoil is the only fluid I will use. 40$ in fluid is worth a 125 transmission in my book any day plus a hell of an hour replacing a trans. Never use gl4/5 mixture. Its just as bad as plain gl5 gl5 should only be used in our diffs.

Redline is 11.99 qt and amsoil is 13.49 you need 2.5 qts it is 100% worth it.

[2_Liter_Turbo]

Never use gl4/5 mixture. Its just as bad as plain gl5 gl5 should only be used in our diffs.

It has been awhile since I looked at GL4 vs GL5 specs, and it seems that I made an error here. You are correct in that you should not use a GL4/GL5 gear oil. It meets the spec, however, even though it can have less than plain GL5, it still has too much of the additive that corrodes the brass synchros.