One of things that occurs to me in this oil discussion is that some of
us have 1.9 engines and some 2.1 and our perceptions may be affected by
this. Though the engines are quite similar the 1.9 has a very basic oil
pressure warning system while the 2.1 has the later dynamic oil pressure
warning system. As posts on this list have shown over the years, people
who use lighter weight oils in 2.1 models can experience oil pressure
alarms as a result. This seldom happens in 1.9s, or at least is seldom
noticed.

The 1.9 has a classic single oil pressure switch that turns off the oil
light at about 4 psi of pressure. The 2.1 has this as well as a second
switch set at about 13 psi. The second switch is ignored unless the
engine rpm is above a certain point, 2000 rpm. Then the oil warning
system starts monitoring the second switch and if it does not have
enough pressure the oil alarm goes off, blinking the led and sounding
the annoying buzzer.

A consequence of the different oil pressure sensing systems is that
people with the 1.9 setup can drive around with low oil pressure,
blissfully unaware, accept perhaps for a dimly glowing oil light at low
idle speed. The 2.1 system is digital, if you will. The current through
the pressure switch does not directly flow through the led like it does
in the 1.9. The 2.1 system does not allow the led to glow only dimly at
marginal pressure like the 1.9 can. If the oil pressure is low, it
triggers the oil logic board which flashes the led at a constant
brightness. At 2000 rpm or above it also sounds the audible alarm. No
way to miss this, ignore it, or think it is normal, like you can in a 1.9.

So, 2.1 drivers can be made clearly aware of a low oil pressure
situation that 1.9 drivers would remain blissfully ignorant of. Put
10w30 in a 2.1 and drive it hard on a hot day. Be prepared for an
occasional oil alarm to jolt you to full attention. Put 10w30 into a 1.9
and drive it hard on a hot day, nothing different as far as the driver
knows. 10w30 must be ok for 1.9 engines then, right? Nope.

Mark