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Old 12-22-2005, 06:30 AM
wagonizzle's Avatar
wagonizzle wagonizzle is offline
Join Date: Jul 22, 2005
Location: philly
Posts: 90

When I start my wag from cold (78, 360ci), gauge reads 60 psi at idle. Then as it warms up, drops to 40 while driving. After a while (30 minutes), when I am driving around town and come to a stop light, gauge steadily drops unitl below 0psi. Once I begin moving, it comes back up between 20-40. In Park, it will come up some as well. Highway readings are ok, just around town that it drops all the way down. I would think if I had no oil pressure for real, I would find out in a hurry. But these readings have been consistent for months, and I hear no change in the engine when the psi drops. The truck runs really well for having x39,000 miles (no idea of history). Faulty gauge? Sender?
1978 Wagoneer 360/TH400/QT
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Old 12-22-2005, 06:51 AM
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chrisnsarah chrisnsarah is offline
FSJ Maniac
Join Date: Sep 24, 2000
Location: Nampa, ID
Posts: 3,282

You should hook up a good quality mechanical gauge if you haven't done so already. It shouldn't drop to zero. Normal pressure is 13 psi at idle according to the manual (and my mechanical gauge). My J10 motor has over 160k on it and it idles around 11 psi using 10w-30. I don't hear any expensive noises or such either. and at cold startup, it shoots to 60 also and gradually drops to around 30 when cruising around off idle. I've had these readings for the last 3 years.
'64 J200 thriftside
'67 J2000 townside custom cab
'68 Jeepster Commando
'69 Super Wagoneer
'75 J10
'79 Cherokee S WT
'75 Cherokee
'61 Aristocrat Lil Loafer
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Old 12-23-2005, 05:35 AM
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mechanical man mechanical man is offline
Master Mechanic
Join Date: Dec 24, 2004
Location: LaPlata, Maryland
Posts: 832

Check it with another gauge. If it really is dropping to zero at idle in gear you probably have 139Kmiles on the motor. That is characteristic of a 360's end of life. Idle oil pressure fades away as bearing clearances open up. Finally a bearing somewhere will fall apart. Mine made it 157Kmiles with low oil pressure for the last 25k or so.
87 GW 96 XJ

87 GW, B.J.s 4" lift, 3.92s, ARBs f&r, 32-11.50-15s BFG ATs, Eldebrock Performer/Holley 4160 4bbl, Thorley headers, Z&M HEI, Flowmaster 70 Series, just about everything mechanical rebuilt.

Other drivers: 06 Sequoia, 82 Avanti, 77 Bronco, 78 C-10 Custom Flatbed, 96 XJ-wife's
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Old 12-23-2005, 06:07 AM
Balming Balming is offline
Join Date: Apr 27, 2001
Location: North Alabama
Posts: 102

Mine does the same thing.

I was wondering about it too, I guess I won't worry about it.

MOLON LABE!!!<BR>.<BR>.<BR>.<BR>1978 Cherokee Chief \"S\" WideTrack 2-door<BR>360, QT-th400<BR>All original, fully loaded with -EVERYTHING- that you could get extra in 78.<BR>Built like a !&%#$@&! tank!<BR>(vibrates like h.e.l.l. too)
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Old 12-23-2005, 07:33 AM
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drlocke drlocke is offline
Roadside Mechanic
Join Date: Dec 29, 2003
Location: Western MA
Posts: 9,725

Originally posted by Balming:
Mine does the same thing.

I was wondering about it too, I guess I won't worry about it.

You actually SHOULD be concerned, and should verify that it is the electric gauge or its sender, and not something more serious. At least put on a temporary direct-reading gauge to make sure that's all it turned out to be. I personally won't take responsibility for operating a vehicle that does not have a direct reading oil gauge. The electric ones are just dashboard decorations.
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Old 12-23-2005, 10:21 AM
illegalFSJ illegalFSJ is offline
Bleedin' Gasoline
Join Date: Jun 03, 2002
Location: Bend, OR
Posts: 2,143

My J10 had very similar oil pressure readings for several years. Since I was (still am) running a cheap junkyard motor in it, I didn't worry too much about the gauge readings. Eventually, I decided to fix an oil leak that dripped down on the front axle. Leak was coming from oil sending unit. Replaced unit, and now I'm at 40psi oil pressure when cruising at operating temp.
"Well, what gears do you have? If you have 2.72s in there still, a blown big block with jesus himself working the gas pedal couldnt get the rear tires to slip." -Mavawreck

1977 J10, shortbed, 360, T18a 4-speed, D20, 32\" A/T tires, Warn hubs - Forest Service Green
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