00_WJ_4.0

So for a while now I've been having a issue with the oil pressure on my 4.0 Jeep. Ran it the other day doing some wheeling and noticed the pressure dropped at idle, comes back some when I'm on the gas a little bit, but again drops when I let off. Its a scary situation because I don't want the thing to blow up on me. Little bit of info on the Jeep, there's literally just over 180,000 on it and it's not run very often. God only knows how long it's been since it was even on the road. only thing I know is that I worry about it and am not all too sure what my best option is at this point...do I replace the oil pump or leave it? Maybe a faulty sensor or not? Idk so please I'd anyone has advice, send it my way. Want her to run good for a long time.

00_WJ_4.0

bigbadon

The only way to know your real oil pressure is to install a test gauge. A tired engine can produce very low pressure at idle, not a big concern as long as pressure returns when rpm increases. My engine has been doing the same as yours for over 5 years and about 70,000 miles! So I don't think it is going to blow up without some warning noises first.

00_WJ_4.0

OK thanks. I would hope not. I do work at a shop so maybe the test is something we can do here. Just something I'm not all too familiar with as a issue so I've never had to do it.

Bustedback

Oil pressure will rise and fall depending on engine RPM. As a rule of thumb you want 10psi for every 1000rpm, 13psi is the minimum.

bigbadon

......13 psi to indicate decent engine condition. Does not necessarily mean engine is getting inadequate lubrication.

jon-d

also if oil is old, hot, or incorrect weight that can result in lower pressure readings.

RubenZ

Usually at startup it should be around 40, when cruising I'm at 40-50 unless i really give it gas. At IDLE its usually below 20 or so. I noticed I got better Oil Pressure when I got rid of the FRAM oil Filter and put the recommended MOPAR one from Wal-mart.

extrashaky

If not, go by Harbor Freight and pick up their $27 oil pressure test kit:

http://www.harborfreight.com/engine-...kit-62621.html

It's even cheaper with one of their 20% off coupons. It's quite easy to use and has a six foot hose so you can drape it across the cowl and watch it while seated in the driver's seat. Just remove the oil pressure sender and screw the hose into the same hole.

If you have good oil pressure on the manual gauge, the sender is probably bad. Replace it with a genuine Mopar sender from the dealer, NOT one of the cheaper aftermarket ones from the local parts stores. The aftermarket ones are notorious for failing, sometimes right out of the box.

If the manual gauge confirms bad oil pressure, post back your results. There's no point in getting all freaked out over the bad things that could be causing that until you confirm it with a manual gauge.

dave1123

If you DO buy a new sensor, buy one for your year. I think it was 2002-2003, they stopped using oil pressure sensors that read actual pressure and were just slide switches that showed 40 psi anytime the engine was running, regardless of pressure. It would read zero if it was low.