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Captain
Dodge Dakota
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6/05/2006
02:10:56
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 Subject: 1992 3.9l oil issues
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Hello,
I've had an ongoing issue with my 92' 3.9 thats been driving me and my local Chrysler dealers nuts.
At start up the oil pressure is great and holds steady. Once the trucks been run for a while (ie-the temp comes up) the oil pressure drops to about 4 psi.While Dodge has assured me that the 3.9 is actually designed to run on a low end pressure of 4psi, the oil warning light still comes on....and I dont like running that low myself.
I've gone to three seperate dealers, and a couple of independant shops, with no conclusive reason found for the problem. They all verify what is happening, but without paying for a complete teardown, they cant tell me anything further!!?
I changed the oil pump myself, and have tried a couple of different oil sending units with no changes to the situation. I have also hooked up a mechanical oil gauge...which verifies the dash gauge.
I am not burning, nor losing oil, so I dont think this is a mechanical issue (the truck runs like new!). I have been told by a couple of people that this condition is caused by an issue with the intake manifold gaskets? Before I rip off the manifold and throw new gaskets on, I wanted to run this by you folks and see what you guys suggest. I have been a "lurker" here for a while and appreciate that there are some pretty Mopar savvy folks on site who may be able to suggest some new ideas for me to follow up with.
Thanks for your help.
Cap
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Joe M.
Dodge Dakota
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6/05/2006
08:01:11
| RE: 1992 3.9l oil issues
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Message:
question
you say the oil pressure is good at first
then after running awhile it drops?
(if i read you correctly)
if that is the case does it climb back up with RPM's though?
my first thought was sending unit or pump
however i see you have already adressed them issue's only other thing i can think of might be sludge
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zzark
*GenII*
6/05/2006
09:03:36
|  RE: 1992 3.9l oil issues
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Message:
what oil are you using?
Have you flushed the engine?
What did the oil pan look like when you changed the pump? How long ago?
zzark
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ElmerFudd
GenII
6/05/2006
09:18:53
| RE: 1992 3.9l oil issues
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There are hundreds of posts on here about low oil pressure and everyone points to three things:
oil pump, oil pressure sending unit, sludge. You changed the oil pump and oil pressure sending unit and in the process should have taken care of the sludge when you change the pump. I would guess something isn't right with the pump.
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bludak
Dodge Dakota
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6/05/2006
13:04:06
| RE: 1992 3.9l oil issues
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If the crank and cam bearings have too much tolerance and are worn, you will have low oil pressure. Nobody thinks of that but I am sure thats what it may be. As the oil warms up and thins out, the pressure goes down. Time for a tear down.
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Scott C
Dodge Dakota
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6/05/2006
13:23:52
| RE: 1992 3.9l oil issues
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Message:
yeah bludak is right.... thats was first thing that came to my mind about the bearing being worn out.. now bearings can be worn ot to point where they wont make noise but show a drop in oil pressure... if he had sludge in the engine he would have noticed when he pulled the pan off and maybe would have said that there was sludge.... you can try a heavier oil like say a 20w50 and see if that might help alittle... it will still thin out some but not as much as 5w30 or 10w30 oil and runnin that oil should show an increase in oil pressure in a worn engine.... thats saying a worn engine as in a non-knocking motor....
Scott C
Royal Auto
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daddio
Dodge Dakota
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6/05/2006
13:40:27
| RE: 1992 3.9l oil issues
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Captain, your dealer is wrong about the 4psi. the FSM states minimum 6spi @ idle and engine warm and @ 3k rpm 30-80 psi. as stated above, excessive cam bearing or main bearing wear could be the culprit. it could just be the brand or weight of oil your using too. if you're using 10w-30 i'd try a 15w-40 or 20w-50. depending on your location you could try a straight 30w oil too.
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Obio3
Dodge Dakota
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6/05/2006
23:21:44
| RE: 1992 3.9l oil issues
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Having only the original statement from captain and with carefull reading . I'm going to say the engine is wore out period. Reguardless of oil used, he has good pressure when cold. that eliminates sludge cause the oil is thickest at that time and if there were sludge restrictions, oil flow would be worse adding up to less oil. Good flow in a worn engine will give reasonable readings till oil starts to thin with heat. Once an engine reaches a certain stage of wear, the relief valve in the pump no longer opens due to lack of preasure . At this point the pump is doing full flow with little resistans to build pressure due to severe wear problems. The milage on the truck, the type of oil used, miles between oil changes, how the truck was driven are all missing issues in this post. the year was stated and going out on a limb i'm guessing high milage. My opinion only.
So many problems .... So little time
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Huggins
Dodge Dakota
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6/06/2006
00:28:16
|  RE: 1992 3.9l oil issues
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I don't neccessarily think that the engine is worn out for a couple of reasons only... #1 The engine doesn't burn or use oil, #2 The engine doesn't leak oil... It's always been my experience that when a engine starts to wear out that it will show signs of oil burn "because the rings will ussually start sticking or wear out long before the bearings will and if it was ill treated sludge would build up between sealing surfaces and cause them to start leaking... To verify that it is actually not burning oil pull a couple of plugs out and look for heavy to moist carbon deposits... The thing that really doesn't consist with worn bearings "to this degree anyway" is the fact that you have good oil pressure while the engine is cold and it only drops after warm up... Now good oil pressure for these engines is right around 50 - 70 psi cold and around 30 - 40 psi hot from my experience... Please specify if this is your good oil pressure while cold or not...
Of course there are some things as previously stated that need to be known such as...
mileage, oil used "weight and brand", oil filter used "fram has had some problems with this as well as the puralator gold or extreme", oil change intervals, how long has this been going on "mileage and time wise", was anything done previously to the engine before this started occurring, driving habits and does oil pressure fluctuate at all with rpm changes???
Something such as a crack in the pickup tube can cause this esspecially if the oil pressure doesn't increase much with rpm increases... The crack being small while the engine is cold will expand making a bigger leak as the engine warms up allowing for good to moderate oil pressure cold then really bad while hot, because all the pump is pumping is air... Now you could also have a bad oil filter combined with a bad bypass valve to make the low oil pressure, but that doesn't account for the good... By this I mean the bypass could be stuck not allowing oil to bypass a clogged or junk filter, which ussually will cause low to no oil pressure...
I really really don't think that a intake gasket will cause this problem in any shape or form, but it wouldn't be the first time I'v been wrong about something...
Keep in mind that oil pressure is just a measurement of how much oil is being allowed to "leak" out into the engine... Good bearings as stated create a tight clearance that the oil must be forced through which in turn creates the oil pressure, so after the engine is warming up you've got a pretty big leak somewhere that you don't neccessarily have while the engine is cold...
Hope this helps a little, but keep in mind that it could very well be a worn engine, but again as previously stated I'v never known an engine to be wore out and not show any signs of oil burn and have bad bearings...
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Captain
Dodge Dakota
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6/06/2006
01:03:05
| RE: 1992 3.9l oil issues
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Wow, thanks for all the input folks!
The engine has 150,000 km on it, and I change the oil EVERY 5000 km. I have always run 10W30 oil, and used the same brand filter and oil since I bought the truck new in 92'. I dont drive it hard. In fact, this truck has kind of become like my kid. I bought a Hemi Ram in 03', and couldnt bear to trade in the Dakota.Except for the oil issue this truck has been phenomenal, and I fully intend to own it as long as I am kicking! The Hemi is a fantastic rig, but theres just something ...right...about the Dakota.
I have heard about the sludge issues, but there was no sign of sludge when I changed the oil pump.
The pressure at cold is (according to the mechanical gauge I installed) around 75 psi, and it drops to 20-25 psi when it warms up.It does stay at that point for a while, then drops down into the basement! I should note that the pressure does come back up with the rpm's.
If I was losing or burning oil, I would chalk this up to rings or valve issues, but I'm not losing or burning any oil. I check the plugs every couple of thousand km's, but have not found any signs of oil fouling, or any other signs of trouble. Theres no knocking....nothing....she even still accelerates like new!
I almost wish something obvious would show up just so I can put the issue to rest...but nothing is jumping out at me. This problem first reared its ugly head in the summer of 02, and it hasnt deteriorated in any way...its really frustrating!
From what you folks have mentioned here, I think the most likely thing may well be the cam bearings...although I would think that would be more noticable? (noise wise).
The motor was one of the MPS (Mopar Performance Series) 3.9's...they only made a few of them in 92. They had a different cam, and a performance distributor...at least the cap and rotor are sufficiently different enough that I can only get them through Chrysler...the generic 3.9 Magnum cap/rotor wont fit.The package was supposed to put out 195HP and 245ftlbs of torque.
Anyway, I'm obviously reluctant to do a motor swap becouse of this, and I fear a teardown may be my only alternative.
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Obio3
Dodge Dakota
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6/06/2006
02:51:23
| RE: 1992 3.9l oil issues
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That's a whole lot of information. So much so I to agree the engine is not wore badly. What if anything did you find wrong with the orginal oil pump. I'm looking for a reason for you to think the pump was bad. How close did you inspect the pickup. Is there a chance the new pump came missing the relief valve plunger or plunger spring. Did you inspect the new pump for these types of things before instalation. Your explaination of oil pressure and how it slowly faids tells me there is no control of flow and as oil heats and thins, it can pass easier or more freely alowing pressure lose. Two things come to mind. Relief valve and by pass valve in filter. Is it possible your using full flow filters with no by pass valve. I can't see a passage restriction as your pressure is good cold. Only other thing coming to mind is a casting flaw in your block alowing oil to seap/leak into the pan while in route. My mind is blank beyond that. maybe smeone else got another idea
So many problems .... So little time
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vern
Dodge Dakota
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6/06/2006
06:24:25
| RE: 1992 3.9l oil issues
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Message:
after reading everything captain has posted this is what i thing is happening,only because i,ve had this happen in the past with a 318 and a 400
these motors get oil to the cam and cam bearings first,plus this is where your oil sending unit gets it reading from,then to rod and mains etc
basic thought on this is you could remove a rod bearing and not get this much oil pressure drop
now with that said i,m thinking the cam bearings/cam are wornin causing excessive oil to exscape when oil is hot/thin,using a heavier grade oil should help with oil pressure,but it won,t fix the problem
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bludak
Dodge Dakota
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6/06/2006
09:55:49
| RE: 1992 3.9l oil issues
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Message:
I think vern has the answer.
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Obio3
Dodge Dakota
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6/07/2006
00:35:51
| RE: 1992 3.9l oil issues
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Message:
With all due respect, He said he used good oil and changed it reg. Also said this been going on sense 02. Never had all these miles on it at that time. He also said it all started in summer of 02. Bearings don't just go away that fast unless run out of oil.Also 150,000 Km just isn't that much miles.
So many problems .... So little time
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Huggins
Dodge Dakota
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6/10/2006
12:54:11
| RE: 1992 3.9l oil issues
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I have to agree with Obio3 here and as vern stated, you could remove a rod bearing and not get this kinda pressure drop... Not only that, but ussually bad bearings will show lower than normal pressure even while cold... 150,000 miles is nothing for these engines and I would think that it should also be nothing for the hopped up performance package that you've got... I would personally be looking for something that would cause this kinda pressure drop at high temps such as the cracked pickup tube, bad relief valve and so forth... BUT in all seriousness, I for one don't think or have never known bearings to just be wore out enough to cause a low pressure after hot and not while warm or cold... Then again if you do have excessively higher than you need valve spring pressures for your performance cam then I guess it would be possible to have wore out cam bearings, but like I've said, I'v never known bearings to cause a low pressure drop like this only when the engine is hot...
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Joe M.
Dodge Dakota
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6/10/2006
14:59:16
|  RE: 1992 3.9l oil issues
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hey guys whats the chances he ran into a bad batch of oil filters??? (by pass valve issue)
he stated he used the same brand all the time
& captain what brand have you been using?
(sorry if you already said and i over looked it)
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vern
Dodge Dakota
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6/10/2006
18:44:26
| RE: 1992 3.9l oil issues
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Message:
a full flow filter is just what it,s called,a full flow no by-pass all oil that is pumped passes thru the filter
a by-pass filter will and does let oil pass by the filter,this means un-filtered oil will be pumped thru the motor not being filtered,this is common in cold weather with a heavier grade oil
a anti drain valve stops oil from draining out of the filter and motor block back to the oil pan
helping with dry starts
a plugged filter will only drops oil pressure usually 8-10psi
bad cam bearings most of the time have great oil pressure cold,normal or very close to normal pressure,But as engine warms oil pressure will start dropping,depending on how much wear is present is how much the oil pressure will drop,
5min of running may-be all the motor has to run to get it down to 0-10psi at idle
the only other thing it can be i think is sludge pluging pickup or captain said he replaced oil pump and may have not gottin it tight or its broke/cracked like higgins said,no matter if no oil is being pumped it,s not good for rod,mains and cam bearings
oh i just read a oil and oil filter article on hughes engines.com that maybe of interest to some of you,i don,t remember where i think under tech
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shatto
Dodge Dakota
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6/10/2006
18:48:55
| RE: 1992 3.9l oil issues
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Captain,
Not long ago I replaced the camshaft on my 98 3.9.
If I was smart I would have left well enough alone, but I replaced three of the four camshaft bearings. Made a huge difference. Oil pressure is now where you say yours is, in spite of replacing the pump.
Now, at night, I put a business card over the 'check engine' light., because I know the pressure isn't really zero.
I'll drive it till it breaks or no longer passes smog, then worry about it.
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Captain
Dodge Dakota
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6/11/2006
17:40:56
| RE: 1992 3.9l oil issues
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I use Motomaster filters from Canadian Tire....I believe Fram actually makes them though, as they use Fram numbers. I have used these on all my vehicles through the years (ALL MOPARS!!!), including my Hemi, and my 91 Dakota.Never had any problems with them.
Once I get some spare time it looks like I'm going to have to rip off the intake and look around!?
I'm kind of wondering if its possible for the oil pump drive to slip? I didnt notice anything when I swapped the pump, and if it was slipping I would think it would show up in the timing...
....I may just go the business card route and drive it till it drops!
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J and J Auto
GenII
6/12/2006
00:21:33
| RE: 1992 3.9l oil issues
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I have only seen this once in my lifetime
chevy straight 6
When the block was poured the casting on the oil
gally between the crank and the cam was thin with
a very small crack that would open when hot and
lose oil presure
This was a new truck and they replaced the entire
motor and gave me the old one
we found it machined a tube on the lathe taped
it in with red locktight put the motor back
togather and the guy put it in his old 65 pickup
and ran it he got a new motor for his old truck
munis the $100 I charged him to fix it
I have never seen this again it was a 1978 chevy
1/2 to 2 wheel the guy bought new 100 miles on
the motor
Larry
J&J Auto
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