So I just started having low oil pressure problems when the engine gets up to full operating temperature and only while idling, I had it diagnosed it isn't the oil pump the mechanic told me to put thicker oil in it to make it last longer so i can save up to get a new engine put in it, so i put 15w-50 in it but the oil light is still coming on but only at idle speed after getting up to operating temperature, i have no idea what else to do other than the idle speed is off, but the dealer told me that isnt adjustable, that it is all done by the computer, what else would cause slow idle and low oil pressure? Thanks in advance. Also i just replaced the o2 sensor before the cat, i didnt have any problems with my jeep other than it not getting up to temps because the thermostat was stuck open so i had that fixed so i could get my heater working again then all of this happened.

 

Get that 15w-50 out of it now!! Thicker oil will just make it harder for the pump to move it, which will prevent the oil from getting to all the places it needs to be.

Check around the engine and make sure you're not leaking at any of the seals. It could be related to the slow idle, which could be the idle control valve.

 

It's leaking at pretty much all the seals but nothing super bad no gushers and i had an additive put in it to swell them back up. As for the oil i was told by multiple mechanics including a friend of my old man that is an expert on cherokees that it wouldnt be a problem, that it should help it

 

Never use heavier oil than the manufacturer says to use, since like i said it just makes it harder for the pump to move so your rockers and valves are not being as well lubricated now. Not to mention it saps the engines power.

Does the cluster have an actual pressure gauge?

 

it doesnt, all i know is im losing oil pressure when its warmed up and idling. unfortunately all ive got in this jeep is the "idiot light"

 

Pff, "Profitable Engineering" at it's finest right? I'm not sure what would cause the low idle but i would try fixing that first. Check the vac lines on the MAP sensor is a good start.

 

Get that 50w out of there bro. 30w is really all you'll ever need. Not going to fix anything, just cause more damage if there is any.

Now I'm not sure if the dummy lights cluster is wired into an oil pressure switch or not, if so I would suggest replacing it first. You can also get your oil pressure tested to confirm you actually have low pressure.

The switch is located right near your oil filter adapter, looks like this: http://www.rockauto.com/catalog/more...081&cc=1431776

You can test the oil pressure yourself if you have the gauge. I couldn't find one to rent, only buy, and was probably only going to use once. So I just bought the new switch and replaced it. I have the actual gauge cluster, my oil pressure was reading 9psi at idle. Occasionally the oil light would pop on, yet the engine was still putting out full performance. I replaced the switch, problem solved.

 

Problem solved! I decided to clean the throttle body I was getting ready to take it apart when I noticed the throttle cable was a tiny bit loose so I put a couple thin popsicle sticks to act as a little spacer and tada problem solved no more slow idle or low oil pressure!

 

I don't see a relationship to that helping oil pressure except for the fact that it may have bumped up the idle just a tad and that raised the oil pressure just enough to keep the idiot light off.

I agree with KJames. You really need some actual data here to make good decisions. Good data = good decisions.

Here is the oil pressure spec for the 4.0.

*Not less than 13 psi at HOT idle
*Between 37-75 psi over 1600 rpms

Call your local parts stores and find one that will rent you a "mechanical oil pressure gauge". It won't cost you much. Remove the oil pressure sending unit and temporarily install this gauge where the sending unit was. Using this technique, you will know exactly what your oil pressure is. If your numbers fall into the spec I listed above, you're good to go.

Also, some oil filters are better than others at keeping your oil pressure up. What brand filter do you use?

 

i did have it checked out, took it to a shop they said it was low after warming up, and i called the dealer they said slow idle will cause low oil pressure. also i use fram filters, and i dont think a throttle cable is supposed to sag at all is it? cause thats what was happening.. last but not least after putting the "spacer" in it idles normally like it used to not high not low but just right, ive had this jeep since it was brand new. im taking out that heavy oil putting in good ol' 10w 30 high mileage like i had before. I found out the mechanic that told me the camshaft bearings had play in them didn't even check them he just assumed because that's "typically what happens" so with all this going on i'm making sure to curse his name a little bit so do you think i should have the oil pan taken off and the pump looked at? every mechanic i have tried will only do that as a last resort because they say "its extremely rare for a mechanical oil pump to ever weaken/fail, im not much of a mechanic im an electronics engineer so this stuff is not in my field ><

 

1. You need to be quite low in oil pressure to trigger the oil pressure idiot light. If I were you, I would like the shop to give me actual PSI numbers to see if you are in spec. Going by whether the idiot light comes on or not is not very accurate. At approximately 750 rpms, you should be at 13 psi or higher at hot idle.

2. I'm not a big fan of the base orange fram filter, the Extra Guard. Some have seen oil pressure issues tied to them. To be fair, I think that their higher end filters are built better and are okay. Wix, Napa, Purolator might be better choices.

3. How many miles are on your engine? A simple compression test is never a bad idea with a high mileage engine. It's a good "snapshot in time" of how things are going inside....

 

it has 172k

 

You have a tired engine with a little wear. You have low pressure at idle...so what's the big worry? That spec of 13psi is for an engine that IS in spec. Low pressure at idle is not a major concern and there is nothing you can do about it anyway unless you want to rebuild. If it makes you feel better I have only 4psi on a very busy DD and it has ran fine for a long time.

 

that fram filter is likely another cause of you're issue. there are threads all over the forum about that junky orange filter being the cause of low oil pressure. do yourself and you're engine a favor and switch to a wix or a mopar filter and run a good 10w-30 oil. here is a little insight what good oil changes and filters do for an engine.

my 4.0 has 190k on it at idle when oil is at operating temp my pressure is 24psi. bump it up to 1600 and it hits 50 psi. i run shell rotella 10w-30 synthetic blend and wix or mopar filters. not overly expensive, not the cheapest but good for protecting and ensuring reliability.

and i agree with checking you're oil pressure you'reself, that shop sounds shade tree already.

 

I've been a bit busy lately so haven't had time to update, anyway i plan on changing the oil to shell rotella 10w30 and a mopar oil filter to see if this helps. I googled fram and all over i see forums about fram causing low oil pressure while hot and at idle.. EXACTLY what ive been experiencing, other than that it runs fine no knocking noises or stalling or surging at all.