Miata Mailing List: June 1992, Message #69
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   From: (none)
Subject: Redline MTL summary
   Date: (none)


Thanks to those who responded to my post, "What is 'Redline MTL?"'  I
summarize them here.

ctsx!ctsx!alan@uunet.uu.net (Alan) writes:
> RedLine is a synthetic (non-petroleum) gear oil.  There are two main
> advantages: it's 'slipperyer' and the viscosity doesn't change with
> temperature.  The second reason is more important to me since my car
> used to shift poorly when the lube was cold (and gooey).  With RedLine the
> car shifts great hot or cold.  It feels like there's Armour-All in the
> gear box!
> 
> Haven't tried it in real hot weather yet, but it's 95 degrees today so I'll
> see if it feels different after work.
> 
> I've been using it since March, haven't had to change it yet.
> 
> I paid $8.95/quart at the local dealer.  I think you can get it less
> mail-order.  The real bitch is that the Miata holds 2.1 quarts so you
> need to buy 3 quarts.  I ended up using 2.4 quarts including spillage.
> 
> I was told to drain the old gearbox oil out for 1/2 hour before
> putting in the RedLine.  It helps to have the transmission hot as well.

After affirming the above, mja@kpc.com (Michael Abbott) adds:
> Mazda recommends certain ratings and weights of gear oils (I think the Miata
> takes GL-4), but not specific brands.  The issue of natural vs. synthetic
> depends more on your "religion" than anything else.  As long as you use
> something that falls within the Mazda recommendations you should be OK.
> Using something outside their recommendations might void your warranty :-(.
> 
> There was recently (might still be) a thread on rec.autos or one of those
> automotive newsgroups comparing GL-4 vs GL-5 gear oils.  Some say that using
> GL-5 in a gearbox that requires GL-4 might damage it because it eliminates
> so much friction that the synchros wear very quickly (synchromeshes need
> some friction to work properly, but the rest of the gears hate friction).
> I don't remember if Red Line MTL is GL-4 or GL-5.

To which tkacik@hobbes.cs.gmr.com (Tom Tkacik CS/50) adds:
> It is GL-4, which is what you want.

To which in turn "STEVE AN"  adds:
> I called Red-Line and they recommend MT-90 (75W90) for the Miata, I used to
> used the MTL (75W80), which I felt got too thin under extreme
> use or when it gets too hot. They are both GL-4 rated. 

Finally, I took a peek in the owner's handbook.  The gearbox oil is supposed
to meet "SPI ...?" (sorry, I wrote it down and then promptly lost it) *and*
"GL-4, GL-5", with no explanatory note about when to use one or the other.
For gearbox oil viscosity, a chart shows that "75W90" is recommended over all
operating temperatures and "80W90" at temperatures above 40-60 degrees F.  The
recommendation from Redline received by Steve An (viz., "GL-4, 75W90") seems
to jibe with the manual's.
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  James Miller -- developing Unix software at (!) IBM -- Austin
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