Fluctuating Oil Gauge???

[My_Little_Pony]

I was looking at my dash the other day when driving and I noticed that the oil pressure gauge was way up at a hair under 80. So, I popped the hood and notice that a hose was loose and I put it back on nice and tight. Started the Jeep back up and it was right back up to a hair under 80. Well I continued to drive and then it started to go down. So, I figured everything was alright. I was driving home tonight and the gauge kept bouncing around between 40 and about 70. What could this mean? Where do I start? Please help!! Is it going to be okay to drive or do I have to drive the gas guzzler around??? Thanks in advance for any help!!

 

[jneary]

your due for a oil pressure sending unit, its pretty common

 

[pabloconrad]

Just as a note, the oil pressure is measured after the filter. When was the last time you changed it?

What year is your XJ? Engine? Any mods? Mileage? A little more info will help us help you. It could be your oil pump is going out, you have a bad filter that let in some debris into your engine (which is bad).

Just a little more info neeed.

 

[jneary]

4.0's rarely have oil pressure problems, if the gauge goes too far to 80 the sending unit is bad, its kinda hard to get too much pressure, however if it was dropping to 0 you would hear lifter/engine noises if it was losing pressure.

 

[XJ_Matt]

If oil filter gets clogged it has a safety valve that bypass the filter and keeps it open so oil flows. I would check the connector of you Oil Pressure Sending unit. It should be right above your oil filter. If the conncector looks good and clean i would then buy a new sending unit. Make sure you get a oil filter and lube job before you put the sending unit in if you havent had one recently as not to contaminate the new sending unit with debris from your old oil.

Matt

 

[My_Little_Pony]

Alright, I am working with an 89 Cherokee Laredo 4.0 automatic. There are no mods, it is completely stock. Mileage, we are not too sure on...it says 231,000 on the odometer, but it was towed behind a motorhome for most of it's life....so, who knows how many actual miles are on it. I changed the oil the day I bought it (04/16/04) and have only put on 1,500 miles. I have recently replaced the water pump, thermostat, and upper/lower radiator hoses. The air conditioning pump just went completely out on me. I know it needs a new serpentine belt also. That is pretty much, all I know to tell you guys. If you think of anything else that might help diagnos the problem let me know.

As for the sending unit, is that something I can replace myself? Should I not be driving the Jeep until I fix that part? Thanks again for all the help.

 

[jneary]

it just threads into a little block by the oil filter

 

[Eagle]

First check the condition of the single wire coming off the oil pressure sender. If the wire is chafed or if the connection where it snaps onto the sender is faulty, you can (will) get inaccurate and potentially erratic readings.

 

[BudTX]

First check the condition of the single wire coming off the oil pressure sender. If the wire is chafed or if the connection where it snaps onto the sender is faulty, you can (will) get inaccurate and potentially erratic readings.

I had the exact same symptoms, and it was a dirty connection at the sending unit.

 

[My_Little_Pony]

The weirdest part of it, is the Jeep drives perfect and the gauge will sit at 40 for awhile, then all of the sudden out of the blue....it will be up at 80 or go down to 30 or sit a around 60....then it will just go right back to normal after awhile. This weekend I will play with the sending unit and hopefully fix it.

The sending unit is that little plug in the back of the engine, right? It has a single (12v looking) wire coming out of it correct? Wait, never mind I am thinking of the bleeder valve for the cooling system......I am lost on to where it is located??????

 

[sportsguy]

My oil guage has been like one of those springie hula dancers you put on your dash - dancing 24/7 since the day I brought the Jeep home (used).I have not worried about it - I have the oil pressure checked once a year while getting other crap done at the shop.

Lifter noise - my truck has sounded like a deisel since the day I brought it home.

Good news is I hear that a certain amount of lifter noise is normal for the 4.0 (I have a '94 HO model). Other good news is that it hasn't really increased or decreased, so I take that it is "normal"

......still, these things make more noises than every other vehicle I have ever owned put together...LOL

I'll second the sending unit replacement. If you're lucky, the suggestions on the connection and/or wire will pan out and save you the time/trouble/money of replacing the actual sending unit.

...sad how you get used to things that are a bit out of whack with your Jeep after a while...*sigh*

Post up when you find the actual fix for your problem.

 

[Tom R.]

First check the condition of the single wire coming off the oil pressure sender. If the wire is chafed or if the connection where it snaps onto the sender is faulty, you can (will) get inaccurate and potentially erratic readings.

Before doing anything, do what Eagle suggests. If the connection looks good, check the wire for chaffing (insulation wear). This can cause it to ground to the block or any other metal source, which will give you erratic readings. Happened to me last Fall. You can tape it up and then use loom to encase the wire, thereby protecting it from grounding out. If this doesn't fix the problem, I'd suggest buying a new oil pressure sending unit from the dealership and using loom to protect the wire from chaffing.

Tom

 

[Yucca-Man]

The sending unit is that little plug in the back of the engine, right? It has a single (12v looking) wire coming out of it correct? Wait, never mind I am thinking of the bleeder valve for the cooling system......I am lost on to where it is located??????

The oil pressure sender is located near the oil filter. Your profile says 89 XJ, and i don't remmeber if it came off the block or the oil filter adapter housing that year. It will look roughly similar to the pressure sender on the left - the right side unit is custom construction.

 

[Kevin]

Was about to post a similar question, but did a search and found this thread. I have a 95 with the manual transmission. Up until a few days ago, I can't remeber the oil pressure ever really reading anything but 40 (straight up). I noticed the other day, that if I get over 2,000 rpms the pressure shoots up past 80. It also shoots past 80 when I change gears, during that brief period of rolling in neutral with no gas, it goes off the gauge.

Oil pressure sending unit????

 

[Eagle]

The 4.0L oiling system has a pressure relief spring that limits oil pressure to either 70 or 75 psi. If the gauge actually hits 80 (or higher), the gauge or the sender is definitely wrong. Sender is more likely. I have 242,000 miles on my '88 and I'm on the fourth oil pressure sender.

Just to be sure we're all on the same page here, bear with me while I review some fundamentals.

1. Oil is thicker (higher viscosity) when cold. It is NORMAL for the oil pressure to be higher when you first start the engine after sitting long enough for it to cool down. With cold oil, 50 psi at idle and 60 to 70 psi at road speed is not unusual.

2. Oil pressure is not constant. The pump is a mechanical pump and it varies in speed with the engine RPM. It spins faster at higher RPM, so the pressure increases at higher RPM. I keep seeing a "rule of thumb" that oil pressure increases 10 psi for every 1000 RPM of engine speed. I have never seen that. What I see in most XJs is idle oil pressure around 30 to 35 psi and highway oil pressure between 50 and 60 psi.

3. No two engines are the same. Oil pressures will vary, depending on temperature, weather, brand and weight of oil, and brand of oil filter. The factory specs aren't all that stringent: 13 psi minimum at 650 RPM idle, and 37 to 75 psi above 1600 RPM. If you are within that range, you're okay.

4. From the above, you can see that the oil pressure SHOULD fluctuate while you drive. Higher speed = higher pressure. Lower speed = lower pressure. If your oil pressure never changes on the gauge, more than likely the sender is stuck.

 

[Kevin]

Thanks Eagle.

Fundamentals are good.