The SAE papers that I read about the
original GM
Oil Life Monitor (OLM) system stated that it only used TIME and TEMPERATURES, there were NO special sensors (viscosity, ph, etc.) involved.
How the OLM works.
GM engineer, Ms. Ellen Shirley Schwartz, PhD, is one of the researchers who developed the GM patent (#6,327,900 B1, dated 11-Dec-2001):
http://www.google.com/patents?id=jpo...page&q&f=false
...the flow chart in Fig. 2 explains which parameters the OLM monitors and measures. Basically, there are three
controlling parameters: the engine revolutions, the oil temperature, and the oil contamination:
• the oil "
temperature (
T) equation" used in the program is:
T(o) = k(2) + k(3)*S(e) + k(4)*T(c) + k(5)*F(q) - k(6)*T(a) ± k(7)*V(s)
...where:
S(e) = engine rotational speed, rpm
T(c) = coolant temperature, șC
F(q) = fuel quantity, cubic-millimeters-per-cylinder
T(a) = air intake temperature, șC
V(s) = vehicle speed, mph
k(2) = constant (-9.0 *)
k(3) = constant (0.012 *)
k(4) = constant (0.95 *)
k(5) = constant (0.21 *)
k(6) = constant (0.001 *)
k(7) = constant (0.01 *)
• the oil "
contamination (
C) equation" used in the program is:
C = k(8) + k(9)*I(t) + k(10)*F(q) + k(11)*T(o) + k(12)*S(e)
...where:
I(t) = fuel injection timing, degrees crank angle
F(q) = fuel injection quantity, cubic-millimeters-per-cylinder
T(o) = calculated oil temperature, șC
S(e) = engine rotational speed, rpm
k(8) = constant (-2.7 *)
k(9) = constant (0.2 *)
k(10) = constant (0.03 *)
k(11) = constant (0.02 *)
k(12) = constant (0.001 *)
* = derived values for GM 6.6L V8 diesel test engine.
Thus, contrary to what Mr. Bob-the-Oil-Guy said, GM is actually tracking "calculated" oil
contamination--
not its ZDDP content--with the OLM...at least, as stated in their 2001 US Patent.