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Old 03-13-2013, 08:14 PM   #1
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Talking Oil Pressure?????

Might be a totally amateur question (sorry... i'm not a mechanic... i'm a musician!) Recently my 6.0 '98 TJ jas been having some oil pressure issues. When I accelerate, My oil pressure drops down to 0 and my "check gauges" light comes on. This is my daily drive (and I LOVE IT!!!) so i need her to be running. What could the problem be here and how much $$ should I be expecting in a quote? I'm definitely going to get an oil change first and see if that fixes the issue...

thanks guys!!!

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Old 03-13-2013, 08:16 PM   #2
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Need to replace the Oil pressure sending unit. Bout $40 at AutoZone.

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Old 03-13-2013, 08:20 PM   #3
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Originally Posted by Hank1550 View Post
Need to replace the Oil pressure sending unit. Bout $40 at AutoZone.
Something i should try and fix myself? or take to a shop? ps... thanks so much for the info!!!!
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Old 03-13-2013, 08:26 PM   #4
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Sounds like you should take it to a shop.
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Old 03-13-2013, 08:27 PM   #5
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It's a DIY project. I'm totally not mechanically inclined but watched a couple YouTube videos of it & no problem. Just type in "replacing oil sending unit in a jeep" & videos are on there.
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Old 03-13-2013, 08:28 PM   #6
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Does he even have any tools?
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Old 03-13-2013, 08:28 PM   #7
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Ya, i'm thinking that's the way i'm going to go. I looked up an install online and i don't have the tools (or knowhow) to do it comfortably... i'd rather not blow up my jeep! thnx!
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Old 03-13-2013, 08:31 PM   #8
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Quote:
Originally Posted by Reaper0726 View Post
Ya, i'm thinking that's the way i'm going to go. I looked up an install online and i don't have the tools (or knowhow) to do it comfortably... i'd rather not blow up my jeep! thnx!
You cannot blow it up but if your not mechanically inclined just removing the connector on a jeep is a big pain.
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Old 03-13-2013, 08:36 PM   #9
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Does he even have any tools?
Yes.... i have some tools. hahaha!
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Old 03-13-2013, 09:57 PM   #10
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If you have a shop do the work, while they have the sending unit out, attach a manual oil pressure gauge to confirm oil pressure. At start up cold/cool should be around 40 psi...warm engine at idle 3-5 is normal. As engine rpm increases so will oil pressure. If oil pressure remains low, you are either looking at an oil pump, cam shaft bearings or both.
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Old 03-14-2013, 01:18 AM   #11
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When I accelerate my gauge goes from 40 then to 60 I assume between 40 and 80. Is that normal? Could that be a oil sending unit as well?
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Old 03-14-2013, 07:31 AM   #12
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Yea, it could be. Or it could be the gauge as well. I have had my 98 since new and the gauges, I.e. the instrument cluster had to be warranted three time within the first 24 months. So, there are issues period with that. Sometimes, just regular ole road and engine grime, mud etc...can seep into the connectors located throughout the wiring harness...water compromise as well can cause high resistance making erroneous gauge indications.

Perhaps the shop you take your TJ to can part the connectors, clean and lub with di-electric grease. So, you may not need a sending unit either. This is a very simple process should you want to try yourself. There clips that need depressing as you pull each connector apart. Purchase electrical connector cleaner from your local parts store and a very small nylon brush similar to a tooth brush and q-tips and a large paper clip and a spray can of di-electric.

Once you part your connectors, you are simply looking for dirt, grime, and corrosion. Corrosion will likely present itself as greenish looking in color. On the pin out (male) side, spray the cleaner and use the brush and q-tips as required to clean. Do the same to the female side but, open up the paper clip and slide it in and out of each psin hole applying pressure to the inner portion, like trying to scratch the sides. This will create bare metal inside the female. Once complete, rinse with the cleaner, let dry, apply the di-electric and what I do for extra seal protection on the connector is, around the male portion of the connector, you should notice something like a seal. Get a small tube of O ring grease or O ring silicone and apply lightly on said seal...connect.

Regarding your oil pressure. Just for piece of mind, have your shop get a mechanical reading of the oil pressure at start up, warm/hot engine idle and highway rpm's. this way you have a basis to compare the same operational snap shot of each condition when connected electrically.

The 4.0 is a very strong and proven engine. I have seen them go Way beyond the rest of the jeep, passing 250-300,000 miles with limited maintenance. The engine loves synthetic oil, and depending on the weight you use, that could increase pressure as well when accelerating. Typical 20w-50 you'll see that unless you have a high velocity oil pump, as I do. Then you could see that with the recommended 10w 30. That said, if you have real high mileage, over 200000, I would just leave the fossil oil. But change it more often. A problem with fossil oils are they breakdown quick comparatively, especially the hotter the engine runs, and over time tends to create sludge in the engine if oil changes frequently go pass 3000 miles. The sending unit simply is a pressure resistant switch, calibrated. Should sludge and engine combustion grime make it onto the orfice of the sending unit, clogging or making that orfice smaller in diameter, that could cause your issue too. So a good cleaning could be in order as well.

Should you try to remove and replace your self, I would spray the inside out first with some spray can parts cleaner. Wash with warm water and dawn dish soap. Spray a little cleaner on a cotton cloth that you could twist in the hole cleaning the threaded area, place some Teflon tape on the threads opposite the direction of tightening, so the tape does not rotate off as its tightened and see if that cures your issue too.

Honestly, this is a very simple repair/ preventive maintenance action. Plus since you have such love with your jeep, it's a way of becoming one, that sounds strange but, it works for me whether I am in my jeep, on my Harley or flying my plane.
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Old 03-14-2013, 09:13 AM   #13
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For what it's worth if you decide to change out the oil sending unit, check your local dealership for the mopar part. I picked one up for under $30 a few months ago - and it was much better quality than what you can get at a pepboys or autozone... As for changing it out - if you're limber you can do it.. biggest issue is just getting a wrench on it from underneath the vehicle... but other than that, it really is a simple swap.
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Old 03-14-2013, 09:52 AM   #14
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Quote:
Originally Posted by rlasky View Post
If you have a shop do the work, while they have the sending unit out, attach a manual oil pressure gauge to confirm oil pressure. At start up cold/cool should be around 40 psi...warm engine at idle 3-5 is normal. As engine rpm increases so will oil pressure. If oil pressure remains low, you are either looking at an oil pump, cam shaft bearings or both.
actually warm idle is 13 psi. Rule of thumb is roughly 10 psi for each 1000 rpms. OP, agree with others regarding replacing the sending unit and also check your oil level.
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Old 03-14-2013, 08:09 PM   #15
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Suggest you read the 4.0 service book. It clearly states 3-5 psi at operating temps is in the normal range at idle. And though your rule of thumb maybe in the ball park in some cases, not all.
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Old 03-14-2013, 11:21 PM   #16
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Don't get confused with all this ninja jeep advice. Really, the oil pressure sending unit is extremely easy to replace.
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Old 03-14-2013, 11:57 PM   #17
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. It clearly states 3-5 psi at operating temps is in the normal range at idle.
You sure? What "service book"?
My 4.0 runs about 40psi @hot idle. Anything below 10psi, on any engine, should start raising red flags...
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Old 03-15-2013, 12:03 AM   #18
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Quote:
Originally Posted by rlasky View Post
Yea, it could be. Or it could be the gauge as well. I have had my 98 since new and the gauges, I.e. the instrument cluster had to be warranted three time within the first 24 months. So, there are issues period with that. Sometimes, just regular ole road and engine grime, mud etc...can seep into the connectors located throughout the wiring harness...water compromise as well can cause high resistance making erroneous gauge indications.

Perhaps the shop you take your TJ to can part the connectors, clean and lub with di-electric grease. So, you may not need a sending unit either. This is a very simple process should you want to try yourself. There clips that need depressing as you pull each connector apart. Purchase electrical connector cleaner from your local parts store and a very small nylon brush similar to a tooth brush and q-tips and a large paper clip and a spray can of di-electric.

Once you part your connectors, you are simply looking for dirt, grime, and corrosion. Corrosion will likely present itself as greenish looking in color. On the pin out (male) side, spray the cleaner and use the brush and q-tips as required to clean. Do the same to the female side but, open up the paper clip and slide it in and out of each psin hole applying pressure to the inner portion, like trying to scratch the sides. This will create bare metal inside the female. Once complete, rinse with the cleaner, let dry, apply the di-electric and what I do for extra seal protection on the connector is, around the male portion of the connector, you should notice something like a seal. Get a small tube of O ring grease or O ring silicone and apply lightly on said seal...connect.

Regarding your oil pressure. Just for piece of mind, have your shop get a mechanical reading of the oil pressure at start up, warm/hot engine idle and highway rpm's. this way you have a basis to compare the same operational snap shot of each condition when connected electrically.

The 4.0 is a very strong and proven engine. I have seen them go Way beyond the rest of the jeep, passing 250-300,000 miles with limited maintenance. The engine loves synthetic oil, and depending on the weight you use, that could increase pressure as well when accelerating. Typical 20w-50 you'll see that unless you have a high velocity oil pump, as I do. Then you could see that with the recommended 10w 30. That said, if you have real high mileage, over 200000, I would just leave the fossil oil. But change it more often. A problem with fossil oils are they breakdown quick comparatively, especially the hotter the engine runs, and over time tends to create sludge in the engine if oil changes frequently go pass 3000 miles. The sending unit simply is a pressure resistant switch, calibrated. Should sludge and engine combustion grime make it onto the orfice of the sending unit, clogging or making that orfice smaller in diameter, that could cause your issue too. So a good cleaning could be in order as well.

Should you try to remove and replace your self, I would spray the inside out first with some spray can parts cleaner. Wash with warm water and dawn dish soap. Spray a little cleaner on a cotton cloth that you could twist in the hole cleaning the threaded area, place some Teflon tape on the threads opposite the direction of tightening, so the tape does not rotate off as its tightened and see if that cures your issue too.

Honestly, this is a very simple repair/ preventive maintenance action. Plus since you have such love with your jeep, it's a way of becoming one, that sounds strange but, it works for me whether I am in my jeep, on my Harley or flying my plane.
That was about 6 paragraphs longer than it needed to be.
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Old 03-15-2013, 12:15 AM   #19
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Ah, not sure the guy needs step by step instructions on rebuilding a motor.....

Back to your problem....

First, check your oil level just to be sure you have some and the level is not below what the dip stick can read.

If your level is visible on the stick it is either the oil sending unit or you have a major oil pressure issue. 99% sure it's the sending unit.

Toss in a new one and call it a day. If the problem goes away with a new sending unit, you are good to go.

If you take it to a shop, they may pull the unit and install a manual gauge just to verify pressure or simply replace the sending unit.
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Old 03-15-2013, 01:10 AM   #20
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Take it to a shop and have them put a master oil pressure gage on it to see if the problem is engine related, or gage related.
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Old 03-15-2013, 07:46 AM   #21
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Quote:
Originally Posted by rlasky View Post
Suggest you read the 4.0 service book. It clearly states 3-5 psi at operating temps is in the normal range at idle. And though your rule of thumb maybe in the ball park in some cases, not all.
You may want to perform the same repairs as the OP if your oil pressure is reading 3-5 psi... Per FSM for 2.5/ 4.0 engine :

Oil Pressure
At Idle Speed (600 rpm) . . . . . . . 89.6 kPa (13 psi)
At 1600 rpm & Higher . . . . . . . . . 255 to 517 kPa
(37 to 75 psi)
Oil Pressure Relief . . . . . . . . . . . 517 kPa (75 psi)
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Old 03-15-2013, 10:13 AM   #22
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So.....what was the final fix?
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Now in a 04 TJ 4cyl 5spd CV @120K+
Both as a commuter vehicle in NW, NJ
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Old 04-16-2013, 04:17 PM   #23
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Well... The problem was in fact the pressure gauge (33$ part). Did an oil change and filter swap as well... Took me about 30 mins to change out the gauge. No big deal at all!!! Thanks for the help!
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Old 07-12-2013, 01:06 PM   #24
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My oil pressure guage hardly ever budges from a tick above 40.

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