Pressure sending unit?
03-14-2013, 04:54 PM
#1
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Year: 1989
Model: Cherokee
Engine: 4.0 L6
Pressure sending unit?
I just got done putting a new motor in my 01 XJ, thanks to the 0331 head. oil pressure is back up to 40-50 psi now, but it drops to around 15-20 at hot idle. I've heard a lot about Mopar sending units working better than BWD (whats in mine now) is there any truth to this? or is it all just rumble?
03-14-2013, 05:01 PM
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Year: 1999
Model: Cherokee
Engine: 4.0L OBD-II
Generally yes, the Mopar sensors are superior, but BWD is not normally associated with crap. That kind of pressure drop is totally normal. If you're concerned rent or borrow a mechanical gauge to test with.
03-14-2013, 08:44 PM
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Engine: 2000 4.0
Don't get too worked up about oil pressure,your numbers are within spec.
Most engine re-builders including the local one here error on the loose side. Clearances in a rebuilt engines are usually targeted mid-spec which may drop pressure but does not hurt a thing. I would rather have this condition then the risk of spinning a bearing. Excess oil pressure is a waste of horsepower and has nothing to do with engine longevity. Oil pressure is the most mis-understood and the most mythed subject in the automotive field. People were more at ease when cars had only idiot lights that didn't flash on until pressure dropped below 3 psi.
Most engine re-builders including the local one here error on the loose side. Clearances in a rebuilt engines are usually targeted mid-spec which may drop pressure but does not hurt a thing. I would rather have this condition then the risk of spinning a bearing. Excess oil pressure is a waste of horsepower and has nothing to do with engine longevity. Oil pressure is the most mis-understood and the most mythed subject in the automotive field. People were more at ease when cars had only idiot lights that didn't flash on until pressure dropped below 3 psi.
03-15-2013, 01:47 AM
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Year: 1989
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Call it me being OCD about that kind of thing lol I'm not worried about the gauge reading, bearing resistance is clearly there or i would hear unhappy lifters for sure. It's more annoying than anything to watch a gauge drop. I just needed some sort of backwards reassurance i'm making a mountain out of a molehill
03-15-2013, 10:18 AM
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Herp Derp Jerp
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Year: 1999
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Nah, it's highly dependent on the oil weight and ambient temperature. Most 10W30s will be 5-6 times LESS viscious at operating temperature than at 40oC. They're even thicker when sitting cold.
03-15-2013, 05:44 PM
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Year: 1999
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Your numbers are okay and within spec; I've seen a variation of pressures between engines. But if you are so inclined, a mechanical gauge would easily verify your numbers and take only a few minutes. This gauge can be rented from many parts stores; call around.
I hope your new engine doesn't have a factory 00-01 0331 cylinder head on it!
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