jebmccall

alright so friday night i go and hit the trails and i go to creep into a mudhole and my front end drops off a little i have a buddy pull me out. leaving the trails i notice that my oil pressure is low 13 psi. get on the highway and it does not really change that much. pull off the highway and come to a stop and my oil pressure drops to 0 and i et a check gauges light. i get going again and it goes up a little bit.

i change the oil in the morning and its got water in it. put new 15w-40 with a mopar filter on it and i have alright oil pressure. i let it run for 30 minutes idling and it stayed around 20-30.

today i take it out on the hihway and as it gets warmer the pressure drops off to about 13-20 psi depending on rpms. pull off the hihway and it drops down to zero until i get going at 2000 rpms then it reads pressure.

i dont believe the sending unit is the culprit because when oil pressure drops off my engine runs hotter like lack of lubrication. it is not knocking at all

i am thinking of pulling the oil pan, checking the main and rod bearings, and replacing the oil pump, if the cranks looks fine im just going to replace the bearings too. what size bearings should i get? do i need to measure the journals? i plan on hooking up a manual gauge to it to verify the issue.

any other suggestions? sorry for the long post..

Gee oh Dee

Deal with verifying oil pressure first, then worry about the rest.

Moncheche

X2 Make sure it's not your sending unit.

Why run the heavy oil? You're not get the lubrication you need.
Bobistheoilguy.com

War Eagle

just block ur oil pressure gauge from your sight...worry when you start getting knocks

tjwalker

Always verify low oil pressure. Takes all of 10 minutes with a mechanical oil pressure gauge, which can be rented from a parts store if you don't have access to one.

Spec oil pressure for the 4.0

*Not less than 13 psi at HOT idle

*Between 37-75 psi over 1600 rpms

Killabrew

I have the exact same problem. Would like to hear what you find. I have driven mine 2500 miles with the oil pressure dropping to zero at hot, in gear, idle. No knocking and still runs fine.

jebmccall

brought my coworkers matco oil pressure gauge home today for best accuracy. cranked it up with sending unit plugged in and the dash read 22-30 psi cold. removed the sending unit and plugged the manual gauge in and fired it up and it read between 50-60 psi. let it get hot and it only dropped down to 17 psi and when revved to 1500 it went between 35-45 psi. i dont know if i used the correct fitting but im guna get a new sending unit tmmrw.

now i still have to pull the transmission to put a new front pump seal in it. ill probably change the filters and fluid while its out. how hard is it to pull th aw4?

jebmccall

update, so i replace the sending unit and it does fine till it gets to temp while driving and it slowly died off. i decided to try replacing the oil pump. i put a new pump in and the oil pressure went to 60 at start up which is higher than before. but once again once the oil thins out while driving it loses oil pressure. im starting to think i need to replace the engine. any suggestions on any thing else i should check first or any suggestions for places to get a new engine?

Firestorm500

I'm sorry to hear that. Your main bearing clearances are probably opening up too much when engine is hot, resulting in low/no oil pressure. They probably burned up when water got into the oil.

10W-30 oil is all you ever need. Heavier doesn't help; it actually hurts.

Moncheche

X2 on the oil. Heavy oil accelerates the end.

If you have the ability to change the oil pump, you can change the crank and rod bearings. Do that, and your pressure will return.

I just did mine.

Firestorm500

He also needs to check the cylinder walls for scoring.

Gee oh Dee

Hope you are kidding.

Gee oh Dee

Got a write up?

War Eagle

if his motor really had zero oil pressure, it wouldnt run anymore...he checked with a mechanical gauge and said it had good pressure

Gee oh Dee

Yes, we know that now. We didn't before.

A motor will run on zero oil pressure, just not for long. But low oil pressure can keep the motor quiet enough to not raise alarm but still cause severe damage.

I would keep the oil pressure gauge visable and working if at all possible. We've been given one to begin with, why not put it to use?