| Re: [GMCnet] Fluctuating Oil Gauge Readings [message #189635 is a reply to message #189620] |
Thu, 08 November 2012 14:10   |
James Hupy
Messages: 6806
Registered: May 2010
Karma:
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Senior Member |
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Keith, It is a matter of the engine design. Modern engines have closer
tolerances and are designed to have higher oil pressure even at idle. The
pumps produce more pressure even at idle then the Oldsmobile does.
Therefore the bypass circuit is in operation even at low engine speed with
the result that there is almost no fluctuation on the guage. Olds engines
for the most part bypass only above 35psi on the stock pump, and when the
engine is running at idle, the camshaft driven oil pump which turns at 1/2
engine rpm does not produce much pressure, which is a result of restriction
to flow. They can be modified to produce higher pressure as well as
increased volume, BUT the oil returns for the heads are not sized to return
a large volume of oil, so the rocker arm covers will retain a good deal of
oil at high engine speed like climbing long grades with the result of oil
starvation to the crank and cam bearings. Not a particularly good thing for
engine durability. They can be enlarged but such work is by hand by experts
and not inexpensive.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Thu, Nov 8, 2012 at 9:55 AM, <enate98690@mypacks.net> wrote:
> Hi,
>
> Does anyone know why the oil gauge readings on the GM/Olds engines
> fluctuate with engine speed (i.e., lower pressure at lower RPM and vice
> versa)? I have seen this occur with other engines but also note that the
> reading on my 2006 Dodge Truck NEVER fluctuates.
>
> I don't believe this is just an oil pressure sender unit issue. It would
> seem that it would be the way the engine is designed with Chrysler etc
> using a system that just relieves excess pressure (to get the consistent
> reading) with GM using a design that just pumps the oil directly to the
> engine based on engine speed.
>
> Does anyone have any information on this issue?
> Thanks!
> Keith Lee
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