oil press warning

Phil Rose pjrose at frontiernet.net
Sat Sep 4 18:07:42 EDT 2004

At 1:41 PM -0600 9/4/04, Henry A Harper III wrote:
>  > >So the question is...  Will over pressure tip off the warning?
>>  There are two pressure sensors--low and high. So, yes, it can react
>>  to excessive pressure. But although I've often seen 5 bar briefly
>>  during warm-up, I've never had the pressure warning. The ECU
>>  considers the combination of RPM and pressure (and perhaps engine
>>  temp) to decide on whether to issue a hi/lo warning. The "critical"
>>  RPM is about 3K, I believe. I'm sure some lister knows the exact
>>  parameters for oil pressure warnings.
>The "high" pressure sensor is actually to check for oil pressure *below* a
>certain level at a particular RPM - 1.8bar at 2000rpm or something like
>that. It's not an overpressure sensor.

Right you are. The oil pressure switch checks for pressures to be  at 
_least_ about 1.8 bar. There is a specified _minimum_ spec of 2.0 bar 
at 2000 RPM, but it's not clear in the Bentley if a warning light 
comes on if that (2.0 bar) is not reached. As to "overpressure" 
situation (meaning oil pressures well above 5 bar): if that occurs we 
don't get a warning light and, according to the Bentley, that 
situation (excess pressure) will just stall the engine due to 
excessive pressure on the hydraulic lifters.

The oil pressure sender (G10)--besides producing a signal 
proportional to oil pressure--evidently also contains a switch to 
cause a warning light for minimum pressure failure-mode (e.g., 
pressure below 0.3 bar) on startup. In the MC engine this function is 
carried out by a separate switch.

Bentley warns that "incorrectly installed" wiring to the G10 sender 
switch (two wires) will cause the Auto-Check oil-pressure light to 
come on. Perhaps just a loose/dirty connection will trigger that 
light (?)

>Umm...20w-50 is the recommended summer viscosity, and it was a "hot day".
>According to the little chart in Bentley. 10w-40/10w-30 should not be used
>at ambient temperatures over 60F

True enough, but too finicky for me. I tend to use 10W30 year-round 
from (a) sheer laziness, and (b) the fact that our local ambient 
temps  rarely warm up  in coordination with my oil-change schedule. I 
know, it's letting the "cart lead the horse". ;-)


Phil Rose
Rochester, NY
mailto:pjrose at frontiernet.net

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