Need Immediate Technical Advice - Low Oil Pressure

Hey guys and gals,
I potentially have a great deal on a 2000 Jeep Cherokee but it has one technical issue that has me contemplating the buy.
After about 10 minutes, the oil pressure gauge drops to zero. The seller has replaced the oil pump and the oil pressure sensor switch. The Jeep runs great with no knocking, pinging (other than valve tick), and is in generally great conditions. So, my questions are:
1. Is this a common error for this year? If so, what is the fix? 2. Is there a pressure sensor probe (like for cooland temp) that senses the oil pressure? If so, could this have gone bad? 3. Could the gauge itself be bad?
The seller is willing to let me take it home for a day or so to test drive it for the weekend. If the Jeep is truly getting zero oil pressure, would it not seize after a few minutes of running?
Any advice is much appreciated!!!
Dave
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On Dec 17, 4:23 pm, snipped-for-privacy@gmail.com wrote:

I would not buy this vehicle, seller has replaced items that would logically fix a "easy" oil pressure problem, Sounds like when the oil heats up and thins out some its just not holding pressure, probably due to excessive wear (and thus too much clearance) on the crankshaft bearings.
S
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senses
beg, borrow, or buy a manual guage and screw into threads where sending unit goes..only way to get a true picture.
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Warm the engine up, disconnect the sending unit and put a real pressure gauge on there. Start it up and read a real number off a calibrated gauge and compare it with the one in the manual.
It's possible for an engine with poor oil flow to keep running without immediate failure but register very low on the gauge. If this is the case, you probably don't want to buy this vehicle. --scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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Scott. Thanks!
By sending unit, are you referring to the sensor that is plugged in near the oil filter? Do I simply disconnect the plug and then plug in the manual oil pressure gauge?
This sounds like a simple test to rule out a fauly dash gauge.
Thanks for the quick feedback!
Dave. Scott Dorsey wrote:

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Yes. A good mechanic can do this for you. It won't take long. --scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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4. Could the drainback holes in the heads be so plugged that all the oil is staying in the top of the engine, and not draining back into the crankcase?
When the gauge goes to zero, what does the dipstick show (running or not)?
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I would not buy a car that had low oil pressure. It is possible that an engine failure is eminent. Check the oil temperature if you can and verify that the pressure sensor is working correctly.

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Great deal -first red flag!

Run away run away!!!!
Even if the seller screws a mechanical guage in there and proves that the engine is maintaining good oil pressure and that the dashboard guage is broken, once you buy it and start driving it, how do you propose that your going to know the difference between a "normal" oil guage reading of zero, and a sudden mechanical problem that would produce a guage reading of zero?

Oh that's a great one. Then over the weekend it seizes and you find yourself in court with the seller telling the judge "it worked fine when I loaned it to him"
The seller is just trying to emotionally snare you so you allow your logic to go out the window. Hell, if your even contemplating touching this, the seller already has you hooked and knows it, and is just working on reeling you in.
If you can pick it up for $300 and you have a crashed Jeep with a perfectly good engine, you might have something.
Otherwise your just going to join the long lines of people who have too much invested in their car to cut their losses and run, so they just keep paying and paying and paying...
Ted
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Dave, I had a similar problem with a 97 Chev Cavalier (120k miles) I recently bought. Engine sounded great and ran great before and after I bought it, but shortly after I bought the car, the oil light started coming on (will do when less than 5psi pressure), only after the engine (and oil) was warmed up. Took it to a mechanic. Turns out it had a new oil pump and head. Mechanic found scored bearings in the cam and crank.. said worn bearings and metal dust inside engine. said the worn bearings were what was dropping my oil pressure, and advised that the engine would eventually throw a rod. (prev owner was a woman...). mechanic suspected that prev driver neglected car, resulting in blown head...and prev repair shop must have replaced oil pump and head in order to patch the problem.
Strait 30 nor 20/50 weight oil did not fix the problem, but strait 50 weight did... but that stuff is really too thick for a 4cyl.
So I ended up replacing the engine, after so many shops refused to replace the cam and crank.
you can get a mechanical oil pressure gauge for around $20 at pep boys and/or O'Reilly auto parts.
so my advise to you is invest in one of those oil pressure gagues, buy the Hayes manual for the oil pressure specs, and take the car home and test it (after engine is warmed up)... otherwise, avoid purchasing that Cherokee.
Tim Sell North Texas.
snipped-for-privacy@gmail.com wrote:

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The dash gauges are known to be faulty. A real mechanical test is called for.
I believe I have even participated in the discussion and testing of the vehicle you are thinking of buying or someone else has done the same things we recently talked about on another forum.
That engine was running perfectly while showing no oil pressure and the owner was getting suckered into more work when everyone on the forum insisted he get the mechanical gauge test. He finally did and the dash gauge was ruled faulty.
Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pictures.html?id !15147590 (More Off Road album links at bottom of the view page)
snipped-for-privacy@gmail.com wrote:

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snipped-for-privacy@gmail.com wrote:

Put a MECHANICAL gauge on it. They're cheap and available at any parts store- don't bother with a permanent installation, just put the capillary tube in where the sending unit goes and tape/velcro/whatever the gauge down while you run the engine. Electric gauges are next to worthless for real troubleshooting, because 9 times out of 10 the problem is the gauge itself.
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