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Unread 09-13-2013, 03:56 PM   #1
DMolyneaux
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1999 WJ 
 
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Zero oil pressure for two years

OK, here is the situation. 99 Grand Cherokee Limited 4.7v8 with @ 250,00K. Began having oil pressure issues only in the Winter and when accelerating. Gauge would go to near or zero, check gauges light would come on. Really weird thing, one morning it suddenly flipped 180 and went to gaining pressure when accelerating and going to zero when idling!!? Now I get intermittent low pressure year round with no consistency of load demand RPM. Changed sensor twice. Sea Foam, filters, additives. Admit, I have not connected an analog gauge to rule out the dash readout being faulty (any other options there??). I do get occasional valve rattle on startup. Is the engine just that good that it can run for @ two years with oil pressure issues like that????

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Unread 09-13-2013, 06:38 PM   #2
uberxj92
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4.7's are not the strongest in the world. You have a lot of miles there.
Connect the aftermarket gauge.
It sounds to me like the bearings are wearing out.
Sea foam lol. Sorry not a fan. Dad and I own a machine shop hes been doing thus for 50 years. We see a lot of sea foamed stuff.
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Unread 09-14-2013, 05:55 AM   #3
DMolyneaux
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Just tried Sea Foam incase I had crud clogging lines. There is not any sign of noise from the bottom of the engine that might indicate bearing wear. Pressure problem is NOT consistant, sometimes it will run at 45-50psi.
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Unread 09-14-2013, 11:17 AM   #4
uberxj92
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Could be the pump. The valve maybe sticking or failing
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Unread 09-14-2013, 01:39 PM   #5
Charley3
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Perhaps the guage sending unit is the problem.

My Buick normal oil pressure range is 65 to 35 psi depening from cold start to full op temp.

One day it started reading 128 psi all the time. I replaced oil pressure sending unit. Problem solved.

Test or replace sending unit before doing anything else.
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Unread 09-14-2013, 01:43 PM   #6
Charley3
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P.S. - why'd you wait 2 years to worry about it?
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Unread 09-15-2013, 12:52 AM   #7
uberxj92
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Quote:
Originally Posted by Charley3 View Post
P.S. - why'd you wait 2 years to worry about it?
Lol me too
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Unread 09-15-2013, 06:04 AM   #8
DMolyneaux
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Sending unit has been replaced twice. Problem has not been ignored just can not seem to find a solution and the vehicle seems to tolerate the condition. If it is a failing pump, the repair is too extensive and expensive for a vehicle with @250k miles on it.
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Unread 09-15-2013, 11:44 AM   #9
Charley3
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Now I'm intrigued.
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Unread 09-15-2013, 04:18 PM   #10
DMolyneaux
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Yeah, so am I. Even if I AM on the wrong end of a puzzle! None of this makes any sense. Thought about an oil pickup tube leak or clogged return lines from the valves. Hopefully the SeaFoam would have cleared up the latter. Clogged or leaking pickup tube does not explain the shift (sudden) from low pressure at load to low pressure at sump (unload). I would think gauge except I DO get occasional valve rattle on start until the engine runs a little. Still not convinced that this engine just runs with very little oil pressure!
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Unread 09-17-2013, 10:56 PM   #11
Charley3
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Time for a professinal certified mechanic, IMO.

If you refuse that, try Mobil One 0-40. It might help some.

0-40 works great in cars that originally used 10-30 conventional.

However, it has extra detergent in oil and will loosen snd remove deposits. So change oil filter at 250 miles, and again at 500 miles. After that every 4000 miles like normal.

The oil itself only needs changing every 8000 miles or 12000 miles.
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Unread 09-17-2013, 10:57 PM   #12
Charley3
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BTW - Motorvac is a pro cleaning. Way better than Seafoam.
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Unread 09-18-2013, 01:02 AM   #13
uberxj92
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Sea foam is dangerous in an old motor be careful
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