Does this sound like a bad oil pressure sender?

I'm looking at buying an '01 with 153k. The owner says that at idle the oil pressure gauge drops all the way and picks up as soon as you blip the throttle. He's been driving it like this every day and says there are no knocks or any other issues. If the oil pressure was really dropping to zero would it have lasted this long? I'm thinking maybe the gauge or sender is just bad? What typically wears out to cause the pressure to drop this low, if it's actually dropping?

How about coolant in the oil...mine does the same thing as you described ('00 XJ) ever since the head cracked (0331 casting!). But only does it after a long warm up or driven on highway for a long while. It does this with the original sensor and a new one I just put in.

He said the head was replaced last year and the oil's always looked good.

Mine does the same thing. Likewise, no problems with oil and coolant co-mingling.

My 96 and 99 both do the Samething. The 96 has 198 K and the 99 has 135K. No coolent in the oil. It only starts after it warms up. once warm the Oil presure will be below 40 and when driving it is just above 40.
Both have new senders.

Well, you can have coolant in the oil and never really see it.

My oil looks good, level never changes...but I know coolant is getting there.

After driving a long distance on the freeway, I can remove my oil cap (no coolant or milky residue there) and look down into between cylinder 3 and 4...there will be steam, bubbles and a slight milky liquid coming up from the head.

But the stuff never shows up on the dip stick, and again, oil level never seems to change.

I'm not saying for sure it is coolant in the oil or cracked head in your case, I'm just throwing that idea out there.

Could be sensor...maybe it is screwed up because of coolant in the oil before...you mentioned the head was replaced...why was it replaced?

This is one of those situations where you can speculate for hours about what might be causing something to happen that may not be happening in the first place.

If it were me, I wouldn't consider buying the thing without taking a few minutes to check the pressure with a mechanical gauge.

Is a bad head gasket the only thing that would cause low oil pressure? I would think worn bearings would do it too. If the gaps are too big then there's nothing to build pressure against.

Well, yes, worn bearings can cause low oil pressure...there are several things in fact...some even claim certain brands of oil filters will cause low readings...

But Pelican is right, all you will get here is speculation and past experience which may or may not apply to your case.

Get a mechanical gauge and do some inspection to make sure...

thebrick said:

Well, yes, worn bearings can cause low oil pressure...there are several things in fact...some even claim certain brands of oil filters will cause low readings...

But Pelican is right, all you will get here is speculation and past experience which may or may not apply to your case.

Get a mechanical gauge and do some inspection to make sure...

Click to expand...

x2 Check it with a mech gauge. If its good them most likely the sender.

I've done plenty of wrenching but I've never happened to use a mechanical oil pressure gauge. I'm sure others are at this same stage as well, so please explain what a mechanical gauge is, whether we should buy or rent one, how and where to hook it up and what the test procedure is.

Buy one if you think you'll need it a few times. It's just what it sounds like, a mechanical gauge that reads pressure.

Procedure - turn off engine, unscrew oil pressure sender, screw in mechanical gauge, start engine, read gauge.

Something like this-

http://www.harborfreight.com/engine-oil-pressure-tester-92687.html

0331 head?

Thanks for the additional info! For $9 it's definitely worth owning one.

If the engine sounds okay at idle with the guage reading zero, I'd bet its just a bad sender.

My bet too. We did have a freak incident happen on the trail at Fall Crawl though.

05 Rubicon (so, DIL + special cam position sensor in place of distributor), the CEL came on and the oil pressure indicator dropped to 0. We checked the DTCs and found 6 cam position sensor related codes. Engine was somehow running fine and sounding fine however... for a few minutes. Someone was stuck up ahead so we were going nowhere anyways and spent some time debugging it. Tried unplugging the sensor to see if it was a sensor/pressure problem or an electrical problem, the gauge changed position so we determined it was either the sensor or it was telling the truth. About 45 seconds later, the #1 lifter started to rattle so we shut it off. Turned it back on to verify and #2/3/4 started rattling. At that point we shut it off, made plans to strap it off the trail, and started cogitating... haven't heard back from the owner yet but our theory was that the oil pump had seized after a very steep hill descent a few minutes prior, chewed up the DIL sensor's input shaft, and probably thrown it slightly out of time, so there really was no oil pressure. If we had had a mechanical gauge on hand we would have had a much better idea what was going on much faster.

Before I bought my '89 XJ the oil pressure gauge was all over the map including dropping to zero at idle. I did not have a mechanical gauge with me so I grabbed a new sender and dropped it in real quick. Oil pressure was fine. The '89 XJ had 178,000 miles at the time. Sure sounds like the sender in your case but be sure before buying.