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Discussion Starter · #1 ·
Question: Have a 98 Dakota, 3.9. Been running full synthetic & new Fram every 3500 - 3800 miles since about 20,000 miles. Have noticed the older it gets, I see a pretty big fluctuation in oil pressure from highway vs idle speed.

Driving @ 65mph it reads about 75psi and engine is quiet. At idle, say sitting at a stop sign, the pressure is 20-25psi and you can hear what sounds like the main bearings knocking. Kick it back on the road and all's well. Is this much difference normal? Now has 115K with no other known engine problems (thank God). Is there an upgraded / high performance oil pump that may solve the pressure drop?

Thanks for your feedback.:D

By the way - not related to this post per se but I just re-did my front brakes. Changed to SP Diamond Slot rotors, EBC Yellow Stuff pads, replaced calipers with Mopar stock ones, flushed brake lines. *The rear are ready (just need the time & better weather) and will replace the drums, hardware, wheel cylinders and PG shoes. Just the front job has made a HUGE difference. Well worth the money and a lot better than when Midas replaced everything.
Highly recommend the rotors/pads!
 

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I think the fluctuation is normal. I remember with my Dakota that the oil pressure would fall when at idle and the raise back up once I got moving. I don't remember the exact psi though.
 

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Discussion Starter · #3 ·
Thanks for the feedback. The knocking at idle concerns me though. A friend has a Dakota V8 with more miles and doesn't have the knock. Other than dropping the oil pan, how much of a pain is changing the oil pump?

Any other 3.9 owners have these symptoms?

Thanks guys!
Al
 

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Discussion Starter · #5 · (Edited)
Either Castrol or Mobil 1, both full synthetic. Does yours also have the bearing knock sound? Mine sounds like the mains, not rods. Haven't looked into an OEM replacement or high performance pump (if there is such a thing), just bothers me. Not sure how hard replacing the pump would be, but may give it a shot later this year.
 

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just a thought

i have a 98 dakota3.9 i had the same noise the only time it made the noise was when stopped it was 1 exhaust mainfold bolt that rusted and broke the bolt still was tight becuase it it was bolted to the heat shield and looked fine but when removing the exhaust manilfold i noticed it was broke and could tell it had been broken for a long time had to drill and easyout the broken blt then replaced the header and havnt heard anthing since that oil pressure is normal and its suppose to fluctuate that much my dakota now has 120k and still running strong
 

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Discussion Starter · #7 ·
layinkota98
Thanks for the feedback. I've had 2 exhaust bolts snap off. A real pain to fix, but I ended up replacing all of them. This noise is definately from the lower half of the motor cause I've crawled under it while running. A mechanic I trust said to switch from Fram to Wix because the Fram filters too much and clogs up too soon, cutting some pressure. Also said to run Lucas oil treatment to conditon seals/gaskets inside. Due for oil change about a month so we'll see.
 

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layinkota98
Thanks for the feedback. I've had 2 exhaust bolts snap off. A real pain to fix, but I ended up replacing all of them. This noise is definately from the lower half of the motor cause I've crawled under it while running. A mechanic I trust said to switch from Fram to Wix because the Fram filters too much and clogs up too soon, cutting some pressure. Also said to run Lucas oil treatment to conditon seals/gaskets inside. Due for oil change about a month so we'll see.
I was just about to say use lucas.....on the subject of oil..ne one else here run royal purple...expensive stuff but you can definately tell a difference...i never thought that oil could gain me that much power
 

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i used royal purple and couldnt really tell that much of a difference in power but could really tell a difference in how smooth it idles and runs... but yea try lucas and it should help you out a lil bit.. o yea i once broke my y-pipe and the exhaust leak made my truck sound like it was knockin but i fixed the leak and it idles great and no weird noises
 
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