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Unread 02-26-2012, 10:43 AM   #1
fitterdude
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2011 WK 
 
Join Date: Jan 2012
Location: , Kentucky
Posts: 13
pentastar V6 oil pressure question

I was wondering if anyone could tell me if this is a normal condition or not:

I've noticed that when the engine and the oil are cold, the EVIC says that the oil pressure is 80 psi (+/- 5 psi or so). That seems very high to me. As the engine warms up and the oil temperature reaches about 150 degrees, the pressure quickly drops and stays in the 30 psi range, dropping to as low as 27 psi. I've never had a gauge that told me the exact oil pressure before, so I was wondering if these pressure variations were ok or should I take it in for service before the oil pump goes out. The engine also uses oil, could this be why?

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Unread 02-26-2012, 11:08 AM   #2
padgett
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2012 WK 
 
Join Date: Feb 2012
Location: orlando, florida
Posts: 582
I went as deep into that subject as possible online and without a factory service manual but apparently it is a two element (mechanical and electrical) oiling system and I suspect part (the relief ?) is under electronic control so if it bothers you, it may be possible to unplug something.

The bottom line is that apparently the designers agree with what Herb Adams used to say about race engines, "at idle you don't need any oil pressure", the factory spec seems to be "over 5 psi" at hot idle so twenty-something is in spec.

It seems to be part of the search for torque and MPG. Below 158F coolant temp, the oil pressure is quite high - I see 60-80 psi at a (Florida) cold idle. Once the magic temperature is sensed, I imagine a bypass opens and the pressure drops to twenty-something idle and high-thirties at 60 mph. Exceed 3500 rpm and the "something" closes and full oil pressure is back.

Back in the day, the adage was "10 psi for every 1000 rpm" and it certainly meets that but is really a function of bearing surface area (do not have all the specs but seems large enough), and loads plus enough flow to keep everything that needs oiling lubricated. Do remember Grumpy Jenkins saying he ran 20 weight oil in the "Toy" because it was worth another 10 hp. Might mention that bearing loads increase with the square of RPM so maybe it is good for another MPG at sub-2000 rpm cruise on the Interstate. They do guarentee the Pentastar for 100,000 miles and the oil change interval seems to be a variable so may be sound.

Frankly, I wonder how much difference it makes and full pressure could be a single unplug away. OTOH the green sheet newsletter of the 70s warned that 55 psi was enough and that too much could wash bearings away. I imagine materials have improved since then. Whether disabling will trip something else or will need a 5 ohm jumper I have not a clue. "The exercise is left to the student" but suggest the engineers probably knew what they were doing.

That said from the specs it looks like it has a georotor oil pump which IMNSHO is far superior to a gear type. YMMV.

To answer the other question, "uses oil" ? On the third tank & mine is still full.


One of these is a diesel.
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