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Old 04-30-2014, 06:15 PM   #1
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Oil Pressure Dropping

01 wrangler pressure is dropping when I stop. It drops down to 0. It's a 4.0. What could be causing this? I don't see any oil leaks.

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Old 04-30-2014, 06:28 PM   #2
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I've got the same problem. I replaced the oil pressure sensor and it didn't help. I have no leaks or loss in performance. I did start hearing a knock so I took it to my mech buddy. This was his diagnoses" your losing oil pressure cause 2 of your bearings are shot in the cylinder. The knock is the lack of oil getting to the top of your block because of the loss of pressure." He advised me to get a new engine, and oh BTW, mine only has 150000 on it. I'm not ready to give up on this engine, gonna replace the oil pump next week. I'm keeping my fingers crossed.

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Old 04-30-2014, 06:38 PM   #3
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Quite a few thing can cause it. Best bet would be to get a Mechanical Gauge (beg/borrow/buy) and check it. Then go from there. Good pressure? Then Sending Unit/Gauge is bad. Bad Pressure still? Bearings/Pump/holes.

I keep a Mechanical gauge around just in case
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Old 04-30-2014, 06:40 PM   #4
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I not hearing any noise. Mine only has 82000 so I definitely not buying a new engine.
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Old 04-30-2014, 07:03 PM   #5
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Had the same issue when I bought an '02 4.0 with 70K.
replaced oil pump. didn't fix it.
Dealership said it was bas crank bearings.

Oil level was full on dip stick, but I noticed that I usually lost pressure when on the brakes.
I added another 1/2 qt, and saw some improvement.
Another 1/2 qt. and pressure loss was less frequent.
Another 1/2 qt. and problem solved.

I need every drop of 6 qts to keep the pressure up.
Try ignoring the dip stick and make sure you have 6 qts. of oil.
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Old 04-30-2014, 07:13 PM   #6
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Quite a few thing can cause it. Best bet would be to get a Mechanical Gauge (beg/borrow/buy) and check it. Then go from there. Good pressure? Then Sending Unit/Gauge is bad. Bad Pressure still? Bearings/Pump/holes.

I keep a Mechanical gauge around just in case
+1 Make sure the oil is full. Then check the oil pressure as per the shop manual and post the readings.
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Old 04-30-2014, 07:26 PM   #7
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I will. With the low miles could it be anything stupid that I am missing? They guy I bought it from didn't use it for over 6 months and it just sat in his garage.
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Old 04-30-2014, 07:37 PM   #8
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I will. With the low miles could it be anything stupid that I am missing? They guy I bought it from didn't use it for over 6 months and it just sat in his garage.

You're not really missing anything. The only question I have is how long is the oil in use? If you have a leaking injector/injectors they can cause the oil to be diluted with fuel and that will also drop oil pressure, and that's not good for the engine. Even if the oil level is full.
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Old 04-30-2014, 08:56 PM   #9
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I checked the oil and it is just at the safe level on the dip stick. With it sitting for so long does anything that it I topped it with some oil and used a engine clean additive to the oil that it would help?
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Old 04-30-2014, 09:10 PM   #10
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Might want to go ahead & Change the oil & filter if you are not sure how old it is or what weight oil is in it now,I would go with a 10w30 oil & Mopar or other quality filter should take 6 quarts including filter.
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Old 05-01-2014, 04:30 AM   #11
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I checked the oil and it is just at the safe level on the dip stick. With it sitting for so long does anything that it I topped it with some oil and used a engine clean additive to the oil that it would help?
Did you add an additive to clean the engine? If so what did you add? Some of these additives contain Kerosene and can thin the oil which would lower your oil pressure. I would also suggest changing the oil and the filter to the recommended viscosity for your engine and see if there is an improvement. Keep in mind it would still be a good idea after you change the oil to get oil pressure readings. Get your hands on a shop manual or Google what your oil pressure should be. They'll probably list a cold pressure at idle and at a certain rpm, then a hot pressure at idle and a certain rpm. Keep in mind the hot rpm reading will take a good half an hour drive on the highway to get the oil good and hot for the proper reading.
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Old 05-01-2014, 07:42 AM   #12
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Did you add an additive to clean the engine? If so what did you add? Some of these additives contain Kerosene and can thin the oil which would lower your oil pressure. I would also suggest changing the oil and the filter to the recommended viscosity for your engine and see if there is an improvement. Keep in mind it would still be a good idea after you change the oil to get oil pressure readings. Get your hands on a shop manual or Google what your oil pressure should be. They'll probably list a cold pressure at idle and at a certain rpm, then a hot pressure at idle and a certain rpm. Keep in mind the hot rpm reading will take a good half an hour drive on the highway to get the oil good and hot for the proper reading.
No additive was used yet. I was curious if anyone thought it was a good idea before I change oil to clean up any possible junk or sludge that could have built up from sitting so long.
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Old 05-01-2014, 08:30 AM   #13
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Cleaning junk/sludge up can be tricky, as you run the risk of dislodging things that might do more harm by plugging oil passages. If it were me, assuming you've ruled out a faulty sending unit and/or gauge, I would start with a conventional oil and filter change. Use this as a way to flush the system, so as not to waste more expensive synthetic oil. You can always change to synthetic later.

If that doesn't work, I would then pull the valve cover and check for sludge up top. The chances are the valve cover gasket needs to be changed anyway, so this will do no harm.
Next, I would pull the oil pan and see if the screen to the pump is plugged. Generally, if I'm going to go to the trouble of pulling the pan, I'll just replace the oil pump. Also, since your in there, you'll have the opportunity to replace the rear main seal. These are a two piece design, which are known to leak. The only thing to worry about with this one is that you take your time and not nick the crank when removing the old seal. Your call here though!

Lastly, word of warning, if you do replace the oil pump, please make sure you prime the pump, i.e. fill it with oil, before you bolt it back in. Also, make sure you remember to torque the oil pump bolts to the proper spec!
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Old 05-01-2014, 10:15 AM   #14
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I have noticed mine drops irregularly when the oil gets close to time to be changed, and after long interstate commutes at 75 or so.
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Old 05-01-2014, 11:03 AM   #15
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DesertRaider's mechanic was right on this one.

If you have changed your oil and filter and if you confirm oil pressure goes to zero at idle when fully warmed up with a mechanical gauge and you don't have a knock yet you will probably be able to get away with replacing the oil pump and the main bearings. One without the other is too risky. Do both. If you have a knock it is too late. You'll need a complete engine rebuild and a new crankshaft.
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Old 05-01-2014, 05:04 PM   #16
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I didn't know what type of oil was in there so I did an oil change with conventional oil. When it warms up it's at 45 or so than at idel or dead stop it at 10-20. I didn't put a different gauge on. This is what the dash gauge is saying.
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Old 05-02-2014, 07:15 AM   #17
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I didn't know what type of oil was in there so I did an oil change with conventional oil. When it warms up it's at 45 or so than at idel or dead stop it at 10-20. I didn't put a different gauge on. This is what the dash gauge is saying.
Those readings are fine, with these two important points in mind.

1. Verify the readings with a mechanical gauge.
2. The engine must be driven at least 30 minutes on the highway to determine the hot idle pressure. Your temp gauge can say the coolant is at normal operating temps, however the oil takes a lot longer to get to its normal operating temperature. A 30 minute drive or more on the highway will guarantee the oil is at the right temperature.
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Old 05-02-2014, 07:35 AM   #18
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I agree, those numbers are fine.
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Old 05-02-2014, 11:29 AM   #19
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My last one had 171k and it never dropped below 40.
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Old 05-05-2014, 09:45 AM   #20
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Your last one was the unusual on then. >12 psi is ok at idle.
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Old 05-06-2014, 06:10 AM   #21
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It's dropping below 12, and the check engine light is on. I don't have the means to put a mechanical gauge on so I'll have to take it in.
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Old 05-06-2014, 09:27 AM   #22
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Just remove the oil pressure sender and screw in a mechanical gauge. You can get one at any auto parts store. This will have everything you need and it is less than $20.

Sunpro Style Line Mechanical Oil Pressure Gauge - Black Dial CP8216: Purchase the best Oil Pressure Gauge at Advance Auto Parts
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Old 05-07-2014, 04:36 AM   #23
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It's dropping below 12, and the check engine light is on. I don't have the means to put a mechanical gauge on so I'll have to take it in.
Bring it in, they'll put a mechanical oil pressure gauge on it and verify the oil pressure. I would not be driving it with the light on, you could have a bad oil pump, or your bearings are bad. You mentioned Check Engine Light, that means you have a code stored which should tell a tech what the problem is. Are you sure its a CEL that's on, and not a light pertaining to the oil pressure or low level warning? Without knowing the oil pressure from a mechanical pressure gauge we really don't know what the oil pressure is.
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Old 05-07-2014, 05:36 AM   #24
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Bring it in, they'll put a mechanical oil pressure gauge on it and verify the oil pressure. I would not be driving it with the light on, you could have a bad oil pump, or your bearings are bad. You mentioned Check Engine Light, that means you have a code stored which should tell a tech what the problem is. Are you sure its a CEL that's on, and not a light pertaining to the oil pressure or low level warning? Without knowing the oil pressure from a mechanical pressure gauge we really don't know what the oil pressure is.
The check gauge light comes on but it hasn't since I did oil change but it still drops. I am taking it in tonight for a full check on everything. I just bought it.
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Old 05-08-2014, 05:08 AM   #25
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The check gauge light comes on but it hasn't since I did oil change but it still drops. I am taking it in tonight for a full check on everything. I just bought it.

Good move! Report back.
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Old 05-09-2014, 04:33 PM   #26
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Took it in. They confirmed pressure with mechanical gauge and it is low. Recommended replacing or rebuilding engine because of the bearing clearances that is causing this low pressure.
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Old 05-09-2014, 06:49 PM   #27
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The oil could be ancient and worn out. change it and a possibly clogged filter then check it
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Old 05-09-2014, 07:19 PM   #28
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The oil could be ancient and worn out. change it and a possibly clogged filter then check it
Already did that and replaced the sending unit.
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Old 05-09-2014, 07:31 PM   #29
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The oil could be ancient and worn out. change it and a possibly clogged filter then check it
x2. I wouldn't rush to spend thousands of dollars on a new engine. I'm sure a mechanic would love you to let him rebuild or install a new manufactured engine. If you don't hear ticking or knocking, the engine is good. Low oil pressure could be simple maintenance issues, such as clogged filters, leaky gaskets, oil low, bad OPS unit, etc.

I would look under you Jeep and see if it is leaking oil too. Check the head gaskets for leaking oil. As mentioned above, change the oil filter, and replace the oil. No ticking or knocking, no engine problem. Diesel engines are just loud too. Some engines are just louder than other engines, regardless of whether they are diesel or not.
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Old 05-10-2014, 10:17 PM   #30
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x2. I wouldn't rush to spend thousands of dollars on a new engine. I'm sure a mechanic would love you to let him rebuild or install a new manufactured engine. If you don't hear ticking or knocking, the engine is good. Low oil pressure could be simple maintenance issues, such as clogged filters, leaky gaskets, oil low, bad OPS unit, etc. I would look under you Jeep and see if it is leaking oil too. Check the head gaskets for leaking oil. As mentioned above, change the oil filter, and replace the oil. No ticking or knocking, no engine problem. Diesel engines are just loud too. Some engines are just louder than other engines, regardless of whether they are diesel or not.
Sending unit replaced, oil changed and full. I see it's wet by head gasket but it's not gushing or look like it fresh oil. What else could it be? It's just hard to believe with this engine and it only having 82k miles that it's need rebuilding or replaced.

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