When i first strat the engine in the morning the oil presure remains
constant in the presure indicator but when the engine reaches the
normal temperature, the presure starts to fluctuate. When i put some
gas the presure gets higher and when i stop the presure goes down. Is
that correct? Is there a oil pump to maintain the presure up when the
engine is cold? Mine is a 99 3.9L!
The oil is thicker when cold, hence the higher pressure.
I had the same problem in my '87 3.9, and '91 5.2.
Had virtually the same in my 1st gen Camaro, when the rear main seal let
go, I had them change the oil pump too.
Now the guage is nice & healthy, definately worth the $ for the peace of
What you are seeing is just wear on the engine. When the oil is cold, it is
thicker and cannot flow as quickly through small gaps so pressure is
constant. As it warms up, it thins down and can more easily flow through
the wider gaps in a slightly worn engine and at idle, there is not enough
volume to maintain steady pressure. When you step on the gas, the oil pump
increases volume output and the pressure goes up. If the lower pressure
bothers you, you can use a heavier weight oil.
If at first you don't succeed, you're not cut out for skydiving
=============Perfectly normal.... as others have noted cold oil has a viscosity
much thicker then warm oil... (try pouring a cup of oil which was
stored overnight in your trunk.. into a coffee cup in the middle of
January... and repeat that experiment again in August) ...oh sorry it
might take you until August to pour that January cup... !
Seriously when the engine is at normal operating temperature the warm
oil is flowing fine...and any change in engine RPM's will change the
oil pressure accordingly....
What I can not figure out is why my 3.9 "sounds" so weird when I first
start in on cool mornings... not a mechanical sound at all...more like
the sound of wind blowing thru bent up ductwork... ????
any ideas anyone... ?
Suddenly, without warning, Bob G. exclaimed (5/19/2005 5:55 AM):
Does it sound like the fan's gone hyperactive? My 4.7 does the same
thing, in a narrow range of morning temperatures (cool mornings, but not
cold). Goes away once I get up to 3rd gear, and stays gone till the
next cool morning.
That is a better discriprion then I could have come up with...BUT
yes it somewhat fits the noise I hear... And yes it is gone until I
get into 3rd gear also... which with my little 3.9 does not require
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