Jeep 4.0 Oil Pressure

[mowlasley]

My 4.0 recently started exhibiting low oil pressure (~5 lbs.) at low RPMs (stopped at stoplight), but only after at least 15 minutes of freeway speed. Slight application of throttle or slip into neutral lets the RPMs up enough to bring the pressure back up around 25 lbs., and just a little more throttle gives me 40 lbs. It is strange to me because the drop in pressure has happened all of a sudden, not gradually.

Is there any chance that my oil pump is going out? Do I gamble and put in a high flow oil pump to try to bring the pressure up, or are the bearings shot and this thing bound for the scrap yard?

The jeep has 211,000 miles on it, and has had a good life. I really don't want to have to go buy another vehicle (poor college student). I guess my question is whether anyone has had low oil pressure on a 4.0 and remedied it with a new oil pump?

Any input is appreciated.

 

[Tacoma]

sounds like maybe bearings are going? I dont' know.

w/that many miles I'd start thinking "REBUILD".... if you're lucky you can get away w/new bearings and gaskets and do it cheap, get some miles out of it until you can afford either a new vehicle or a proper rebuild.

 

[mowlasley]

I don't doubt that the bearings are severly worn, but it isn't making noise, or have excessive blow-by, which I would expect if the bearings were totally shot.

Talking to Skiba's down in Spanish Fork, he seemed to think that a rebuild would not be worth the money, nor would a new engine. So do I take the gamble and replace the oilpump, which may or may not help?

 

[rust bucket]

Try changing the oil with a 10w40 or a 15w40 oil that is for a higher milege vehicle[like valvoline max life] That should help with the presure.
Also try a 5min oil system cleaner with the oil change.It will help losen wp any debris or sludge in the motor.

 

[Tacoma]

hmmmm

the oil pump might be your cheapest gamble at this point. Certainly won't hurt anything.


I'm curious why a rebuild isn't worth it? Is the rest of the truck shot?

 

[mowlasley]

Skiba talked like it would not be rebuildable, but would need a new engine. Maybe I should talk to another shop?

A new engine would be $3000+ according to them, and that is not worth it on a 10 year old vehicle worth about $3000.

Any suggestions on an engine rebuilder? I don't have a garage, and can only borrow garage space for a few days at a time, so its not like I can do an overhaul myself, even if I knew where to start.

 

[Tacoma]

It should be rebuildable. It will be cheaper to get a long block from a junkyard if you go that route. Pretty straightforward to just swap a motor out. SHould only take a few days, even if you've never done it before.

 

[mowlasley]

Do you know a good shop for rebuilds on the 4.0 so I can get a quote?

 

[Tacoma]

I don't... it will be pricey to have them do it. You might try looking around for a lower mileage motor in the yards, say $500 tops for a longblock? maybe even less.

You pay for a shitload of labor if you have the shop do it. It's just bolts man! You can do it!

 

[mowlasley]

Okay, so mine is a '95, what are the year ranges that are compatible with it? I agree that it is only bolts, but with no garage, hoist, etc., it would be quite an adventure to do it myself with my limited wrenching experience. I have replaced accessories(water and ps pumps, starter, etc.), but have never even cracked the oilpan myself.

The other issue there is, say I do get an engine out of the yards, its a gamble as to whether it is any better than what is in it now, right?

 

[Rusted]

I am in kind of the same boat as you. Low oil pressure at low RPM, and 210,000 miles. I have been debating between rebuilding my own for the satisfaction of knowing how to rebuild an engine, or buying a rebuilt engine (been watching this thead) because it should be done right. I am figuring that the price will be a little cheaper if I build it myself, but not a lot cheaper.
The killer for you would be the labor. Do it yourself with a rented or borrowed hoist is cheap and would take a few days of crawling around in the mess. But if you don't have that option a shop labor fee will cost at least the price of the engine, and that hurts.

 

[JoeT]

$3000 for a motor!WTF!! Dude must be buying a new boat soon. You should be able to get it rebuilt for half that price!

 

[mowlasley]

$3000 for a motor!WTF!! Dude must be buying a new boat soon. You should be able to get it rebuilt for half that price!

That's what I thought. Give me a shop that will rebuild it for a reasonable amount (~$1500 is the most I would want to spend).

 

[mowlasley]

I am in kind of the same boat as you. Low oil pressure at low RPM, and 210,000 miles. I have been debating between rebuilding my own for the satisfaction of knowing how to rebuild an engine, or buying a rebuilt engine ( been watching this thead because it should be done right. I am figuring that the price will be a little cheaper if I build it myself, but not a lot cheaper.
The killer for you would be the labor. Do it yourself with a rented or borrowed hoist is cheap and would take a few days of crawling around in the mess. But if you don't have that option a shop labor fee will cost at least the price of the engine, and that hurts.

How long has it been having low oil pressure, i.e. how long has it survived in its current state?

 

[Tacoma]

Okay, so mine is a '95, what are the year ranges that are compatible with it?

I think all the 4.0's are compatible. Post...'96? has a better intake manifold design, but you'll be reusing your stuff.

I agree that it is only bolts, but with no garage, hoist, etc., it would be quite an adventure to do it myself with my limited wrenching experience

Borrow a garage, rent a hoist, and get on it. You can have the motor out and back in, in a day, and buttoned up the next if you work away. Even on your first one.

The other issue there is, say I do get an engine out of the yards, its a gamble as to whether it is any better than what is in it now, right?

not really. There are a lot of wrecked Jeeps in the yards. Good ones mark their stuff w/mileage and whatnot and keep the motors seperate and dry. I've used junkyard engines without complaint for a few vehicles, and they ran fine... just have to call around...

now, back to topic LOL

 

[mowlasley]

now, back to topic LOL

Yeah, quit trying to hijack my thread by talking me into an engine swap! At least you didn't suggest an SBC swap!

 

[Brett]

Just a long shot, but you could always check your oil pressure sending unit to see if it's failing. Mine would always read low when they started getting gummed up.

 

[mowlasley]

Just a long shot, but you could always check your oil pressure sending unit to see if it's failing. Mine would always read low when they started getting gummed up.

Tried it with two different guages. I wish it were that, I really do.

Anyone have opinions as to the usefulness of a new high-flow oil pump?

 

[Brett]

Tried it with two different guages. I wish it were that, I really do.

Anyone have opinions as to the usefulness of a new high-flow oil pump?

Tried different gauges or tried new oil pressure sending units? Gauge won't make a difference if the sending unit is bad

 

[Tacoma]

hehe Hijack over.

I say check the sender, if it's bad, toss some Lucas oil treatment and a high volume pump in there. The Lucas saved a ridiculously worn 360 last summer... LOL made it across the country w/12psi at 65mph.. ugh

the pump you can reuse when you finally swap the motor