Miata Mailing List: September 1993, Message #160
sponsored by



     


   From: Herb Samuels 
Subject: Re: 5W-30 and synthetic oils
   Date: Mon, 20 Sep 1993 19:01:21 -0400

I first changed to synthetic oils when I installed a BBR turbo.  I used 
Castrol Syntec (5W-50) first and then recently changed to Mobil I 5W-30. 
Interestingly, both oils show similar oil pressures when the engine is
fully warmed up; slightly less than 30 at idle with the Castrol
slightly higher than the Mobil I and at 3,000 rpm a pressure of about
45.  I was surprised to find that the Mobil I exhibited a slightly
higher pressure over 3,000 rpm than Syntec.  In any case, with either
oil start up lifter noise is virtually non-existent.  I never heard it
with the Casrol.  I've only had the Mobile I in for about 2 weeks.  I
started it up yesterday after not driving it for a week and there was
no lifter noise.  Before either of these, I would hear lifter noise with
conventional oils within a month of changing the oil.  Since the Miata
is usually dirven at high RPMs to achieve maximum power, it is
possible that conventional oils break down faster than we think at
high RPMs.

One other point concerning manual transmission fluid.  About 2 months
ago I changed to Redline MT-90 (75W-90).  I originally asked for
Redline MTL which is a 75W-80 but the Redline person who took the order
said that they did not recommend the MTL.  However, Rod Millen sells 
MTL only for the Miata.  I didn't notice any difference between the
MT-90 and the stock manual transmission oil.  I called and recently
spoke with one of the chemists at Redline.  He told me that the order
clerk does not recommend MTL because Mazda recommends a 75W-90 for the
Miata.  However, he said that they have done extensive testing and
that MTL is perfectly safe (he said that it actually is a 75W-85 at
higher temperatures).  I recently changed to MTL and the transmission
is now really smooth with no evidence of any notchy shifting which I
only had from 1st to 2nd when the engine is cold.  Shifting feels not
only smoother but more precise.  MTL is worth a try is your shifting
is not a smooth as you would like.


Herb Samuels