Oil pressure drop

Mcnenc1

Mcnenc1

TJ Enthusiast
Joined
Feb 11, 2019
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Location
Tampa
Okay so I think I know what this is and how to fix it but before I do I wanted to hear your opinions.

2004 Jeep TJ Sahara 4x4. Automatic


Oil pressure sits perfect while Rpms are higher than nuetral. But once I place the Jew in park OR I’m in drive and sitting at a red light my oil pressure drops to 0. UNTIL I accelerate the rpms then and only then will the oil pressure gauge come back to normal. Everything is tight nothing loose.

Another Problem: while accelerating from stop to about 35mph the 1st gear going into 2nd gear is hard. The Jeep lurches and the gear makes a “clunk” sound after it successfully goes into 2nd. Any idea what causes this or any fixes?

Other than this everything works smoothly and fine. THANKS!
 
Had almost same issue happen with mine, very very good chance you need new oil pressure sending unit. Mopar units are not cheap.

I don't have experience with your transmission. I'm sure someone else will chime in.
 
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Cornbread said:
Had almost same issue happen with mine, very very good chance you need new oil pressure sending unit. Mopar units are not cheap.

I don't have experience with your transmission. I'm sure someone else will chime in.
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Thanks for the fast reply. This is what I thought. Any good websites/places to buy this? How much are we looking at for that part?
 
I went to the dealership and bought it for $75 about two months ago. Almost made me sick because that part looks like it was produced for $0.99..... But multiple members of this site recommended the mopar over the vastly cheaper aftermarket opsu's. I don't think they are supposed to be any good.
 
Mcnenc1 said:
Thanks for the fast reply. This is what I thought. Any good websites/places to buy this? How much are we looking at for that part?
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Also consider this, the original mopar opsu in your's lasted 15 years. Mine lasted 19 years. $75 for 15 years of worry free, no hassle oil pressure reading isn't too bad I guess.
 
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I had the exact problem. Mine was a worn out oil pump. My choice was a new oil pump, $1100.00 installed. Or a new engine, $1800.00 for a long block with a 7 year warranty, plus installation. I did the engine replacement and resolved the leaky rear main seal, valve cover gasket and got a tight engine with noticeably better compression. Might even be getting better gas mileage too.

All in with a new clutch, water pump, rad plus plus, $4700.00 Worth every penny.

I did mine at 190K miles. And there was no doubt, it was a lack of oil pressure, not the sender unit.
 
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Mcnenc1 said:
Okay so I think I know what this is and how to fix it but before I do I wanted to hear your opinions.

2004 Jeep TJ Sahara 4x4. Automatic


Oil pressure sits perfect while Rpms are higher than nuetral. But once I place the Jew in park OR I’m in drive and sitting at a red light my oil pressure drops to 0. UNTIL I accelerate the rpms then and only then will the oil pressure gauge come back to normal. Everything is tight nothing loose.

Another Problem: while accelerating from stop to about 35mph the 1st gear going into 2nd gear is hard. The Jeep lurches and the gear makes a “clunk” sound after it successfully goes into 2nd. Any idea what causes this or any fixes?

Other than this everything works smoothly and fine. THANKS!
Click to expand...

How many miles does the Jeep have on it?
 
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For $30 I bought an oil pressure gauge at harbor freight, at idle and warmed up mine was running a shy 60 psi. 120k miles original motor. How many miles do you have?
 
bromel said:
That doesn't make sense. You're getting 60 psi at hot idle?
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Seems somewhat high to me too. That’s idling in the driveway for 5 min hot, not driving for 30 min. Temp was up to 210 though. I run 15w-40 in everything I own so that should make it higher also. With the new sending unit my hot idle shows about 42 degrees on the dash. Either way I’ve got good oil pressure.
 
Remember that the gauge is measuring the coolant temperature, not the block temperature, so the oil is still warming up even when the coolant reaches operating temp.

Out of curiosity, why are you running 10w-40 in winter? I used to dump 10w-40 in my Cherokee with 250k miles and bad valve seals, but you've only got 120k. Thicker oil might do some damage on cold starts.
 
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bromel said:
Remember that the gauge is measuring the coolant temperature, not the block temperature, so the oil is still warming up even when the coolant reaches operating temp.

Out of curiosity, why are you running 10w-40 in winter? I used to dump 10w-40 in my Cherokee with 250k miles and bad valve seals, but you've only got 120k. Thicker oil might do some damage on cold starts.
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It’s actually 15w40, the reason I run it year around:

1. I put 1500-2000 miles a year on my Jeep so I don’t want to change oil for the winter with that low of miles. Most of my jeeping miles are spring-fall, try to mostly just fix/upgrade it during winter months, not drive it.

2. The main reason I run 15w-40, not 10w-30 as the manual suggests, is because my dad buys Shell rotella 15w-40 by the 50 gallon drum (we use it in everything from our atvs to farm tractors). So I run it in everything and never had an issue. Guess you could say I like my oil like I like my beer, free and on tap! 😂
 
As you also said above, my oil was probably not all the way heated up. I really wasn’t concerned about knowing the exact psi, just wanted to make sure my sending unit was bad and my oil pressure was not “zero”.
 
I have 140k original miles. I’m going to replace the oil sending unit, new oil with filter this weekend. What oil do you guys recommend for a 2004 TJ 140k miles on it daily driver in FL so no cold weather here
 
Mcnenc1 said:
I have 140k original miles. I’m going to replace the oil sending unit, new oil with filter this weekend. What oil do you guys recommend for a 2004 TJ 140k miles on it daily driver in FL so no cold weather here
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10-30 is the best buy, maybe 10-40 in Florida.

Low miles in Florida, the motor should be fine. When you say low oil pressure what happens cuz with mine, the gauge dropped to zero, the red low oil light came on plus there was an audible alarm.
 
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billiebob said:
10-30 is the best buy, maybe 10-40 in Florida.

Low miles in Florida, the motor should be fine. When you say low oil pressure what happens cuz with mine, the gauge dropped to zero, the red low oil light came on plus there was an audible alarm.
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Okay awesome and yes exactly this what you just said
 
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