Little to NO Oil Pressure
- Thread starter JeepinAaron
- Start date
- Location
- Harrisburg, NC
parkeruph said:
Valve Cover Gasket, Oil Filter Adaptor, Rear Main Engine Seal....check those in that order. Those are the 3 most common oil leaks on the 4.0.
Chances are yours is one of the first two.
parkeruph
NAXJA Forum User
- Location
- Hudson, CO.
Thanks Casm & Tim,
I'll check tomorrow, too cold and dark now.
Thanks Guys. Wayne
I'll check tomorrow, too cold and dark now.
Thanks Guys. Wayne
Ecomike
NAXJA# 2091
- Location
- MilkyWay Galaxy
I Had the same problem last year with my 87 Wagoneer, 4.0 L.
First I would get rid of the Mobil 1 oil immediately. Use Exxon or Quaker State 20W-50 Wt. Also use a quart of Lucas oil additive in place of one quart of the oil.
Then if the pressure is still low at idle (say less than 15 to 20 psi at 200 F) then drop the oil pan, check and and replace as needed the crank shaft main bearings and possibly the lower rod bearings on the crank. Inspect them first of course.
Search crankshaft bearing replacement procedures for the how to details (I had an experienced engine mechanic friend of mine do the bearings on mine). Also I suggest replacing the oil pump with a high volume oil pump (I assume they are available for the 99, they were for my 87).
Mine has never used or burned oil since I bought it used 3 years ago, but the warmed up engine idle pressure dropped from about 20 to 10 psi one day last year and I got busy doing the above. My crank- piston rod bearings were OK, but the Main crank shaft bearings had plenty of normal wear on them, enough to lower the gauge pressure. It was time to change them. Lucky for me the crank shaft journals were fine, so I had no need to pull the crank shaft.
My pressure starts at 50 psi now on cold morning start ups and after a long highway cruise followed by a long idle at a stop light at 200 F it holds steady at 20 PSI on the 100 F summer days here. The manual says 13 psi is the lowest for the older 4.0 engines. Not sure of the lower pressure limit on the newer 97 and newer engines.
I run straight Exxon 20W-50 WT oil (or Quaker State if I can't get Exxon), in the winter right now and the same with a quart of Lucas oil additive in the very hot summers here in Houston.
Also, while working on corroded grounds, loose connectors including battery connections, etc., I have noticed that when my voltage meter drops due to heavy power loads (A/C, Blower on high, headlights on and loose alternator belt, or loose or poor ground or battery connections, you get the idea) that my oil gauge pressure will read a little lower (3 psi lower) than normal! Normal being good grounds, good battery connections, good 100% capacity alternator, an not having every electrical load turned on at once including brake lights and head lights, or in other words good gauge voltage on the volt meter!
My point is that I notice about a 3 psi gauge variance at idle when I turn on and then turn off all the large electrical loads in the car, including A/C, Blower on high, headlights on, brake lights on, then try again with them all off and watch the volt meter move with the oil pressure meter. I just fixed a weak ground on mine, so I need to recheck and see if that fixed the 3 psi variance.
Good luck
Mike McGinness
South Houston, TX
First I would get rid of the Mobil 1 oil immediately. Use Exxon or Quaker State 20W-50 Wt. Also use a quart of Lucas oil additive in place of one quart of the oil.
Then if the pressure is still low at idle (say less than 15 to 20 psi at 200 F) then drop the oil pan, check and and replace as needed the crank shaft main bearings and possibly the lower rod bearings on the crank. Inspect them first of course.
Search crankshaft bearing replacement procedures for the how to details (I had an experienced engine mechanic friend of mine do the bearings on mine). Also I suggest replacing the oil pump with a high volume oil pump (I assume they are available for the 99, they were for my 87).
Mine has never used or burned oil since I bought it used 3 years ago, but the warmed up engine idle pressure dropped from about 20 to 10 psi one day last year and I got busy doing the above. My crank- piston rod bearings were OK, but the Main crank shaft bearings had plenty of normal wear on them, enough to lower the gauge pressure. It was time to change them. Lucky for me the crank shaft journals were fine, so I had no need to pull the crank shaft.
My pressure starts at 50 psi now on cold morning start ups and after a long highway cruise followed by a long idle at a stop light at 200 F it holds steady at 20 PSI on the 100 F summer days here. The manual says 13 psi is the lowest for the older 4.0 engines. Not sure of the lower pressure limit on the newer 97 and newer engines.
I run straight Exxon 20W-50 WT oil (or Quaker State if I can't get Exxon), in the winter right now and the same with a quart of Lucas oil additive in the very hot summers here in Houston.
Also, while working on corroded grounds, loose connectors including battery connections, etc., I have noticed that when my voltage meter drops due to heavy power loads (A/C, Blower on high, headlights on and loose alternator belt, or loose or poor ground or battery connections, you get the idea) that my oil gauge pressure will read a little lower (3 psi lower) than normal! Normal being good grounds, good battery connections, good 100% capacity alternator, an not having every electrical load turned on at once including brake lights and head lights, or in other words good gauge voltage on the volt meter!
My point is that I notice about a 3 psi gauge variance at idle when I turn on and then turn off all the large electrical loads in the car, including A/C, Blower on high, headlights on, brake lights on, then try again with them all off and watch the volt meter move with the oil pressure meter. I just fixed a weak ground on mine, so I need to recheck and see if that fixed the 3 psi variance.
Good luck
Mike McGinness
South Houston, TX
parkeruph said:
Here is a picture of a head with SN# 0660
http://www.i29.photobucket.com/albums/c288/jeepinwi/cylinderhead002.jpg
Last edited:
parkeruph
NAXJA Forum User
- Location
- Hudson, CO.
Thanks for the pic SS01XJ
JeepinAaron
NAXJA Forum User
- Location
- NC
I pulled the valve cover today. I did not see any cracks in the head, or anything that looked like water/coolant mixing. The only thing that I noticed was on the valve cover, at the back of the engine around cylinders 5&6. It was some gunk that was built up on the valve cover, it was kind of brownish and gooey. Could be evidence of water up there but i dont know. So it looks like i dont have a cracked head. I added some more h20 and coolant today so I will keep an eye on it if I'm loosing water and checking the oil for milkiness.
Oh and one other thing, there seemed to be plenty of oil reaching the top of the head into the valves/lifters. So it seems that even with only 6psi the engine is getting lubed.
-Aaron
Oh and one other thing, there seemed to be plenty of oil reaching the top of the head into the valves/lifters. So it seems that even with only 6psi the engine is getting lubed.
-Aaron
99XJSPORT06 said:
Blaine B.
NAXJA Forum User
- Location
- Northwest Indiana
I bet it was a tense moment, right up until you didn't see any cracks?
JeepinAaron
NAXJA Forum User
- Location
- NC
Yea, I am still just hoping someone will steal it during the night.
So, can someone give me the down and dirty on replacing the bearings? I suppose I need to replace the main and rod bearings. This can be done with the engine still in the jeep? I've heard that half of the battle is getting the oil pan off but I've already mastered that part.
I know that I am not getting the bearings over sized since I'm not machining the crankshaft, what size do I need?
-Aaron
So, can someone give me the down and dirty on replacing the bearings? I suppose I need to replace the main and rod bearings. This can be done with the engine still in the jeep? I've heard that half of the battle is getting the oil pan off but I've already mastered that part.
I know that I am not getting the bearings over sized since I'm not machining the crankshaft, what size do I need?
-Aaron
Blaine B. said:
Last edited:
Ecomike
NAXJA# 2091
- Location
- MilkyWay Galaxy
Here is what little I know. You need to the pull the oil pan, pull the bearings and inspect them first to see if they have any wear on them. Then, if they are worn, how bad is the wear? The Haynes manual has some (maybe even enough) pictures and details on what to look for and how to decide what to do next (what to install size wise) based on what the bearing races look like. You will also need to get a micrometer or caliper and measure all the crank journals in several spots. Your Hayne's book covers that too. Then you can decide what bearings to buy and use!
Even after I had my crank shaft main bearings replaced (they had some wear), I still had to go to a heavier weight oil in the summer (20w-50 wt) with Lucas oil additive to hold a minimum 20 psi at idle when hot, and that was with the new high volume oil pump upgrade.
The manuals say that 13 psi minimum at idle, fully warmed up is OK for Jeep 4.0's, but it scares the hell out of me to see it drop under 20.
Mine runs as high as 50 psi when cold, before and after the changes.
Once again though, I would consider changing the oil to 20W-50 wt with a quart of Lucas oil additive and measure the hot and cold oil pressure before dropping the oil pan and going after the bearings.
Mike McGinness
South Houston, TX
Even after I had my crank shaft main bearings replaced (they had some wear), I still had to go to a heavier weight oil in the summer (20w-50 wt) with Lucas oil additive to hold a minimum 20 psi at idle when hot, and that was with the new high volume oil pump upgrade.
The manuals say that 13 psi minimum at idle, fully warmed up is OK for Jeep 4.0's, but it scares the hell out of me to see it drop under 20.
Mine runs as high as 50 psi when cold, before and after the changes.
Once again though, I would consider changing the oil to 20W-50 wt with a quart of Lucas oil additive and measure the hot and cold oil pressure before dropping the oil pan and going after the bearings.
Mike McGinness
South Houston, TX
Last edited:
JeepinAaron
NAXJA Forum User
- Location
- NC
I understand how to pull the bearings. My question is this: say they show signs of wear and need replacing. In purchasing new bearings, should i get them over sized or undersized? I read that unless I am getting the crankshaft turned that I shouldn't get them oversized. The hayes manual has a confusing chart of size configurations.
And i dont think its the pressure relief valve since that is located on the oil pump, which i replaced.
And reading other posts about low oil pressure, it seems that its my bearings.
-Aaron
And i dont think its the pressure relief valve since that is located on the oil pump, which i replaced.
And reading other posts about low oil pressure, it seems that its my bearings.
-Aaron
Ecomike said:
Ecomike
NAXJA# 2091
- Location
- MilkyWay Galaxy
Yes, I edited out my comment about the pressure relief valve when I re-read your original post. Sorry for the confusion there.
Wish I new more about the replacement bearing selection process. Logic tells me if the crank shaft is within OEM specs to get the regular (not undersized) "standard" bearings that you are replacing. From what I am reading it sounds like undersized bearings (meaning the bearings are larger and used for an undersized, ground down to a smaller diameter, crank) should be for taking up the gap, space left from turing down a damaged journal race.
Where did you see the term "over sized"? All I see is standard and at most four progressively larger amounts of undersized.
Mike McGinness
South Houston, TX
Wish I new more about the replacement bearing selection process. Logic tells me if the crank shaft is within OEM specs to get the regular (not undersized) "standard" bearings that you are replacing. From what I am reading it sounds like undersized bearings (meaning the bearings are larger and used for an undersized, ground down to a smaller diameter, crank) should be for taking up the gap, space left from turing down a damaged journal race.
Where did you see the term "over sized"? All I see is standard and at most four progressively larger amounts of undersized.
Mike McGinness
South Houston, TX
old_man
NAXJA Forum User
- Location
- Loveland, Colorado
OK, here goes on the bearings. You won't be able to change the size of the bearings (see note at the end). You would just replace the bearings with the same size. This gets rid of the gap caused by the wear. If you know how to pull the bearing cap and the associated tasks, get some plastigage and check the clearance before you waste your time. The bearings may be fine. The problem may be somewhere else.
You should be able to tell the size of the bearings since many have the size on the back of the babbit. The key issue with swapping the bearings is to get the same size and to make sure the crank isn't galled. If the crank is rough, don't bother with the bearing swap, you will need to have the crank turned.
Now for the note I mentioned. I said you will need to replace with the same size bearings. That is not absolutely true. Some manufacturer's make bearings that are not what we call zero-zero bearings. They have a bearing that is a few thousandths smaller for doing just what you are doing. They run from .001 up to .003 from my experience, depending on the application. You can use these if you plastigage and verify the clearance.
I have actually dropped a crank with the engine in the car, then had it ground and put it back in with the new bearings. The only reason I did it was because funds were lacking and the motor had very good compression.
You should be able to tell the size of the bearings since many have the size on the back of the babbit. The key issue with swapping the bearings is to get the same size and to make sure the crank isn't galled. If the crank is rough, don't bother with the bearing swap, you will need to have the crank turned.
Now for the note I mentioned. I said you will need to replace with the same size bearings. That is not absolutely true. Some manufacturer's make bearings that are not what we call zero-zero bearings. They have a bearing that is a few thousandths smaller for doing just what you are doing. They run from .001 up to .003 from my experience, depending on the application. You can use these if you plastigage and verify the clearance.
I have actually dropped a crank with the engine in the car, then had it ground and put it back in with the new bearings. The only reason I did it was because funds were lacking and the motor had very good compression.
Ecomike
NAXJA# 2091
- Location
- MilkyWay Galaxy
I have just been doing some interesting reading on oil and oil filters in this forum. From what I have just read our oil pressure problems can be caused by a bad or defective oil filter!
Try changing your oil filter and use a different brand filter than the one you have now and see what oil pressure you get.
Also, what brand oil filter do you have on the jeep now?
From what I have read, some filters can cause excessive pressure loss through the filter. Some reported a 10 to 30 psi pressure drop
from these filters that was elliminated when they replaced the new filter with another filter (usually a different brand). It is not clear to me yet whether it is a just a case of a defective filter (internal defects of some kind), specific brands and part numbers causing the pressure drop, or a mixture of both. :dunno:
They also reported problems with the anti-drainback valves in certain brands that lead to engine wear in the early seconds of engine starting!
Search "motor and oil and filter" in this forum for intersting reading and more details if you want to know more.
I am planning to go buy a few oil filters (different ones) and run some oil pressure tests and start up pressure tests of my own after what I read.
I will start by getting rid of the Quaker State (turns out it is private labeled Fram) oil filter I just had installed yesterday.
Mike McGinness
South Houston, TX
Try changing your oil filter and use a different brand filter than the one you have now and see what oil pressure you get.
Also, what brand oil filter do you have on the jeep now?
From what I have read, some filters can cause excessive pressure loss through the filter. Some reported a 10 to 30 psi pressure drop
from these filters that was elliminated when they replaced the new filter with another filter (usually a different brand). It is not clear to me yet whether it is a just a case of a defective filter (internal defects of some kind), specific brands and part numbers causing the pressure drop, or a mixture of both. :dunno:They also reported problems with the anti-drainback valves in certain brands that lead to engine wear in the early seconds of engine starting!
Search "motor and oil and filter" in this forum for intersting reading and more details if you want to know more.
I am planning to go buy a few oil filters (different ones) and run some oil pressure tests and start up pressure tests of my own after what I read.
I will start by getting rid of the Quaker State (turns out it is private labeled Fram) oil filter I just had installed yesterday.
Mike McGinness
South Houston, TX
Ecomike
NAXJA# 2091
- Location
- MilkyWay Galaxy
old_man said:
Old man! Can you also help us with the oversized, undersized, smaller, larger terminolgy on these? I think many people are calling larger, smaller and smaller, larger but meaning the same thing. I have searched the forums and seen a hint of clarification, but not a real clear one.
I think the problem is that when we switch from the diameter of the journal (OD) to the (ID) of the bearing it gets confusing for us newbies. The Haynes manual calls them both undersized, but for those of us still trying to get the lingo straight we are thinking a smaller OD jounal means we need a larger bearing but it also means we need a smaller ID (more material inside) bearing. Is this right? Can you explain the terminology better? I have seen some in other discussions call it oversized but then others later call it undersized in the same thread.
Thanks,
Mike McGinness
South Houston, TX
This may be your fix, rebuild the motor. I had the same prob. as you are describing and found out that the rings were worn on the pistons. This was producing blow by there for no presure. Look in your air filter and the crank case vent tubes to see if there is any oil, if so you have blow by through your rings. With my new rebuild I now have presure around 45-50 driving and 35-40 while at idle. You could also get a compression test done to test the rings. Good luck.
Blaine B.
NAXJA Forum User
- Location
- Northwest Indiana
Oil in the breather/air filter could also mean a clogged PCV.....not as serious and such.
JeepinAaron
NAXJA Forum User
- Location
- NC
I'm using a mobil 1
I was using another one, dont remember the brand. But this has been with two different oil filters so thats not it either.
-Aaron
I was using another one, dont remember the brand. But this has been with two different oil filters so thats not it either.
-Aaron
Ecomike said:I have just been doing some interesting reading on oil and oil filters in this forum. From what I have just read our oil pressure problems can be caused by a bad or defective oil filter!
Try changing your oil filter and use a different brand filter than the one you have now and see what oil pressure you get.
Also, what brand oil filter do you have on the jeep now?
From what I have read, some filters can cause excessive pressure loss through the filter. Some reported a 10 to 30 psi pressure drop
They also reported problems with the anti-drainback valves in certain brands that lead to engine wear in the early seconds of engine starting!
Search "motor and oil and filter" in this forum for intersting reading and more details if you want to know more.
I am planning to go buy a few oil filters (different ones) and run some oil pressure tests and start up pressure tests of my own after what I read.
I will start by getting rid of the Quaker State (turns out it is private labeled Fram) oil filter I just had installed yesterday.
Mike McGinness
South Houston, TX
Blaine B.
NAXJA Forum User
- Location
- Northwest Indiana
I'd second that. Plus, if you do redo your engine, you'll need a brand new sender anyway to be sure everything is in tip-top running condition 
Merry Christmas!
Merry Christmas!
