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! CLT.
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 mind.
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.
============== 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... ?
. Bob Griffiths
Air bubble in the cooling system?
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.
jmc
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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 much time... Bob G
Take a look to the fan, may be it need some work!
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