Miata Mailing List: April 1994, Message #36
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   From: a.mccombs3@genie.geis.com
Subject: Re: Valve Chatter
   Date: Sun, 3 Apr 1994 09:37:26 -0400

Tom, back last fall when we were getting serious about Miatas, I test drove
about eight or ten, and I recall two to four of them that had some valve
clatter on startup for anywhere from one to three seconds (approximately).
Most of these were stone cold at startup, although some had been driven
relatively recently and were lukewarm; I don't recall any that had just been
driven hard and shut down immediately before I hopped in and fired it up.
MIleage on these cars ran from as low as 20k or so up to 70+k; I don't
recall any particular correlation between mileage and valve noise.
 
This seemed to be a sufficiently high sample that I asked John Duff, of the
Mazda Sports Car Club of Washington (DC), about it when I ran into him at a
dealership where I was looking at yet another Miata or two.  He said there
are no recalls on this, and that it is somewhat unusual, but not unheard of
(obviously), as I recall.  He didn't seem to think it was any big deal, so
long as the noise went away after a very few seconds.  Whether it is lifters
which have drained and need some time to refill (that would seem unlikely,
given the startup very shortly after shutdown that you describe) - or just
what, I don't know.  At the time, I attributed it to poor maintenance by
previous owners (all the above cars were used '90 - '91 models) who had
failed to change oil as often as required, and had gotten rid of their cars.
 I wrote off any cars displaying such symptoms from my list.  The '90 Miata
we ended up purchasing displays no such symptoms, although the previous
owner had let some major maintenance items go on it (like the timing belt
replacement at 60k).
 
Why the difference in different cars?  --Idunno.  Just WPG (wild posterior
guessing) here, but I assume it has to do with tolerances, both new and as
the engine wears, the oil used (both weight and additives), previous oil
used and any deposits left behind thereby, frequency of oil changes, etc.,
etc.  (Yeah, I know, big help).  Since it might be a matter of partially
blocked oil passages somewhere, have you thought about trying some super
detergent additive?  Can't hurt anything (hopefully!) to try.  However, I
suspect the opposite - relatively rapid drainage from the lifters and a
second or so for the oil pump to fill them again on startup.  So why doesn't
it happen when it's cold or under moderate driving?  Ya got me.
 
Some cars are picky not only about the viscosity of their oil, but also
about the additives and particular brand.  Once had a'71 Pinto, 1.6L engine,
which was happy enough on about anything, so long as it received regular
maintenance.  Gave it an oil change once, and it smoked to high heaven when
we drove away. After a couple miles, it was evident that it wasn't just oil
spilled on the exhaust manifold or some such thing.  We took it back, and
they questioned us about the brand of oil we'd been using.  Answer was
nothing in particular, but the shop had been primarily using Pennzoil.  This
shop put in Quaker State, as I recall (don't hold me to those exact brand
names, but that's what I recollect).  They drained the stuff they'd just put
in and installed the (Pennz or whatever we'd been using before), and the
problem was solved.
 
NOTE:  This is NOT to say that one major brand of oil is all that much
better than another, or that QS (or whatever) is junk, but that some engines
get used to a particular oil's "feel", by which I mean viscosity, additives
(in addition to the detergents or dispersants), etc.  Some of these things
may loosen up deposits, get by rings and/or seals, etc., whereas the other
stuff did not - hence, the smoke.  The lifter noise at startup under some
conditions may be analogous; again, just a WAG.  Keep us posted on what your
experiments turn up on this.
                                                          --Jack M.--