Oil Pressure: How low is too low?

I have a 2002 4.7L Jeep Grand Cherokee. When the engine is hot in the summer, traditionally the oil pressure has been had 40 psi while moving, 25-30 psi while idling. Yesterday it got down to 20 psi while idling. Something to worry about or no? When do I worry? When it gets down to zero while idling? If it’s no longer normal while moving? I’m out of town so I can’t do a whole lot to troublshoot unless it’s a serious issue.

Moved to General Questions from Great Debates.

IANAM, but I wouldn’t be concerned by a 20psi hot idle oil pressure. Most of the indications you are seeing in your gauge cluster are massaged by the ECU anyways, and not actual values. They show what Chrysler has decided their average consumer wants/needs to see. I’d start to pay attention when the needle shows 10psi at idle or 25psi at 1500rpm. It wouldn’t surprise me one bit if the oil pressure actually is 10-15psi at idle when the engine is hot and it’s 100°F outside.

13 - 75psi is the factory specs for my 2001 XJ Cherokee.

You can buy a factory service manual for about $10 online and find out your specs for sure. Jeepforum.com is also a resource I use, along with the SDMB of course.

And if it gets stuck at zero I wouldn’t drive it at all.


This is where I bought my FSM for $7.95 a few months ago.

Assuming you are inclined to keep an eye on oil pressure, and in addition to monitoring the pressure itself, watch for pressure drop when you turn. A drop while doing so is a sure sign you need to add oil.

I’m seeing specs of 7 psi at idle, 35-105 psi at 3000 rpm. Its being less at idle than previously could be because the weather is extremely hot, the oil is old, the oil pickup tube is getting clogged, or there’s mechanical wear in the engine.

ETA: Assuming the oil level is okay.

7 psi is definitely low, very low. Assuming crankcase is full, there aren’t many explanations other than the two you point out as well as a bad oil pump. If a high mileage vehicle, I’d say engine wear is most likely. Regardless, and short of a repair, your only option is to go with a thicker oil. If you live in a warm climate try a straight 40W. It may sound a bit extreme, but it should help.

My wife had an Audi A4 V6. Apparently the Turbo 4 versions are liable to hot oil creating gunk and clogging the input screen. It happened with out non-turbo V6. For the first few years, the dealer did what the manufacturer specifiec, which at that time did not mandate syhthetic oil. When the car was 6 years old she took it to a lubrication place and had the oil flushed first. After that, the oil light came on often when you backed off the throttle.

The dealership said the whole feed after the pump and sensor must have been clogged until the flush. Therefore it registered just fine pressurewise, while the engine was starved for oil.

The thought was that the worst wear was in the crank bearing races, and perhaps replacing those would help - $10,000 worth of work to see if the engine still had a problem? No thanks. Basically we traded it for all of $5,000 (for a car worth about $12,000), and now my wife gives the dealership the finger every time we go by.

So low pressure could also mean the oil outputs have worn so much that there is not enough prssure to oil the extremities of the engine. However, if that is happening, is it worth fixing or just run it til it dies?

The oil is a bit low and it’s old. It’s at the bottom of the “safe” level and it’s beyond 3,000 miles. I didn’t have a chance to get it changed before I left on the trip. As I’m in the midwest (Missouiri) it’s also expierienced a lot of hot weather.