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Unread 07-27-2010, 03:27 PM   #1
ek1
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oil psi at idle

Hey jeepers, I recently bought a 97 Tj 4.0, 105,000 miles. I have 6 qts of 10-30 in it. My oil pressure holds steady at about 42 when driving, but my warm idle psi drops to about 10 and bounces from there to 12 and back. This seems a bit low to me and I thought i would get your opinions.

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Unread 07-27-2010, 03:54 PM   #2
demon67
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sounds like a bad gauge to me
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Unread 07-27-2010, 05:22 PM   #3
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Screw a mechanical guage in it and see what it really is.
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Unread 07-27-2010, 06:36 PM   #4
madmilitia
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mine does the same but at warm idle it sits at about 20
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Unread 07-27-2010, 06:38 PM   #5
makaioM3
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Mines does the same when warm. I have 135,000 miles on my 4.0. I'm not too worried about it.
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Unread 07-27-2010, 06:47 PM   #6
DevilDogDoc
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Well per the big book min psi at hot idle is 13. Above 1600 36-75
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Unread 07-27-2010, 10:49 PM   #7
ek1
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I also read somewhere chrysler says it can operate at 3-4 psi at idle. I'm not really comfortable with it being that low. i actually have a mechanical gage sitting in my garage. I'll hook it up and see what happens. thanks for all the input
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Unread 07-28-2010, 02:31 AM   #8
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Mine was idling ~20 psi, and was running around 40 psi when driving. Changed the oil today and it was idling close to 40 and 50 at ~2k rpms. Used 10w-30 oil, but filter was switched from fram to purolator. Not sure if that would affect it.
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Unread 07-28-2010, 06:36 AM   #9
Skyryder
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I didn't like the low oil pressure at idle either. I would be going slow on the trails and trying to "idle" over an obstacle and the chime would go off. I changed to 15-40 and the problems went away. BTW I have the 4 banger and yes i know that is normally diesel rig oil.
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Unread 07-28-2010, 08:00 AM   #10
DevilDogDoc
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I'm a fan of the 15/40 myself, Rotella flavor
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Unread 07-28-2010, 09:20 AM   #11
Jerry Bransford
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Quote:
Originally Posted by ek1 View Post
Hey jeepers, I recently bought a 97 Tj 4.0, 105,000 miles. I have 6 qts of 10-30 in it. My oil pressure holds steady at about 42 when driving, but my warm idle psi drops to about 10 and bounces from there to 12 and back. This seems a bit low to me and I thought i would get your opinions.
That sounds perfectly normal, I would not be concerned. A good rule of thumb for acceptable oil pressure is approx. 10 psi per thousand engine rpms which means it is supposed to rise and fall in step with engine rpms. On newer TJs, they reprogrammed the gauge so it doesn't do that because it was unnecessarily alarming those who grew up on idiot gauges but on earlier TJs like your '97, it works like an oil pressure gauge is supposed to.

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Originally Posted by DevilDogDoc View Post
I'm a fan of the 15W-40 myself, Rotella flavor
Why would you want 15W instead of 5W or 10W when the engine is cold/cool? Running a 15W just means the oil won't flow as easily after the engine is first started when the engine and oil is cold.
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Unread 07-28-2010, 03:39 PM   #12
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Quote:
Originally Posted by Jerry Bransford View Post
Why would you want 15W instead of 5W or 10W when the engine is cold/cool? Running a 15W just means the oil won't flow as easily after the engine is first started when the engine and oil is cold.
Jerry I have started my Jeep in -7deg in Kansas running 15-40 Rotella, The lifters did rattle for a moment but no problems and I have run it for 100k miles, my oil press is still just fine and it sounds & runs like it did the day I drove it off the lot 10.5 years ago....well sorta it doesn't have any driveshafts in it right now and won't for awhile but I did start it a week ago & she fired right up after 8 months of not being run.
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Unread 07-28-2010, 04:13 PM   #13
Jerry Bransford
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Annecdotal stories aside, there is no doubt that 5W or 10W oil will flow throughout and thus protect the engine faster when cold than 15W will.
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Unread 07-28-2010, 05:01 PM   #14
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Originally Posted by Jerry Bransford View Post
Annecdotal stories aside, there is no doubt that 5W or 10W oil will flow throughout and thus protect the engine faster when cold than 15W will.
You are absolutely right Jerry and if I lived in the cold climate I would run 5w-40w Rotella Synthetic.
One needs to run what weight oil for the climate he/she lives in.
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Unread 07-28-2010, 05:22 PM   #15
DevilDogDoc
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Because where I live I doubt that 5 is really gonna change very much in the grand scheme of things. I started running Rotella back when it was zinc rich but now it's just habit I suppose. Besides isn't that flow number at like 0 degrees or something? Aside from all that 15/40 is factory fill in export TJ's so it can't be that bad for it right?
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