OK, a little oil pressure. The needle is right near the bottom though.
[ul][li]1999 Jeep Cherokee with >200,000 miles[/li][li]Hasn’t been used since September or early-October[/li][li]Started once for about five minutes a month or so ago, just to make sure it ran[/li][li]Overnight temperatures in the high-teens to low-20s[/li][li]Current temperature 27ºF[/ul][/li]
I started it up and left it for a few minutes, then noticed the pressure was very low. I checked the dipstick and there’s enough oil in the engine. Is this a case of oil that’s been sitting in the cold (very cold for nearly a week)? Or is it a mechanical failure?
I noticed that the snow over the engine bay had melted, so I went out and tried again. The needle stayed low for about five seconds, and then jumped back to normal (about 40 to 45 psi at idle).
I’m letting it run, and will be checking it very, very frequently.
No knocking. Engine is 4.0l-six. No idea of the oil weight. I’m assuming 20W-50, since that seems to be pretty standard.
Just took a ride to the gas station for a cuppa joe, two miles distant. Oil pressure is normal at about 50 psi. Engine temperature is normal at 210º. Roads are incredibly slippery. I slid around a corner in 4WD, and normally I don’t in the snow.
Factory recommends 10-30. I would think 10-40 would be a good choice considering your mileage. To be honest, if it didn’t knock I would think the sending unit has junk in it and it got stuck on the low side. If you have a low oil condition a straight 6 will start hammering pretty quickly. I wouldn’t sweat it but I’m sure Rick or **Gary /B] will be along shortly to offer better info.
I remember in the old days I would run a couple of quarts of trans fluid in the crankcase to clean it. The pcv system on these things are kind of janky.
In some oil pressure units the oil in the unit is separate from the oil that comes up the little line from the engine. The oil in either place can become so cold that the pressure from the engine does not cause oil to transfere enough pressure to cause the gauge to register. Used to happen regularly in older small aircraft.
Could be 10-30. I stopped driving it in April, when I got the Prius – except in September when the Prius got smacked. Lots of miles on it. Five or six trips hauling a heavy trailer from L.A. to NoWA. Other than that, mostly loafing along on the freeway. I’ve thought about having it overhauled when it hits 250,000.
That would certainly explain why the engine didn’t knock, but the indicated pressure was very low. Of course in an aircraft I’d shut it down if there was no indicated pressure after 30 seconds.
The Jeep didn’t want to start at first. I had to crank it a worrying amount. Maybe I should have pumped the gas? (It’s fuel injected, and pumping the gas is not SOP.) Anyway it started. Oil pressure started up in about a second, slowly at first and then right on up to normal. I let it run about 10 minutes to get things circulated and to let the alternator charge the battery a little.
My guess is that the sending unit was affected by the long time not being used and/or the cold air temperature. I doubt that the pressure bypass would have stuck open the last time that you drove the Jeep, and I suspect that a pilot would notice these things.
Re, the slow startup: even in the best of conditions, Jeep 4.0s take a while to start. The gas might have been a little stale, and the battery was probably weak from not being used for three months.
Usually the engine catches right away. I’ve noticed though, that if it doesn’t start right up and I let off the key too soon that it will take a lot of cranking. I’m guessing slight flooding in that condition. I drove it four miles yesterday, to the gas station and back. Stale gas? I thought ‘there is no fuel like an old fuel!’ Actually, I topped it off with about 13 gallons yesterday. I replaced the battery two or three years ago.
It seems much colder this year than last year. Maybe I’m just not remembering, but ISTM that it shouldn’t be this cold until the end of January or first part of February.
I would check the sending unit. I’m not familiar with your specific engine but the pump looks like a typical cam/dsitributor shaft driven unit. If you’ve ever taken one apart you’ll see that there isn’t much to go wrong with the mechanism. they don’t lose pressure quickly from wear so it would have to be something like a cracked pickup, or oil gallery plug leak. Rick could probably tell you if there are any pressed-in oil gallery plugs or pressure relief valves that could fail.
Assuming you have hydraulic lifters you would hear the rocker arms rattle if they pumped down due to really low pressure.
At 23 degrees I wouldn’t worry too much. There are three external oil galley plugs on your engine and if any of them were leaking you would know about it right away. The biggest problem in the oiling system of your vehicle is the oil filter housing which uses 3 o-rings to seal it to the block. If it was leaking there would be oil everywhere. Your oil pump is a cam driven unit, also driving the distributor. Any loss of oil pressure would result in severe knocking. Your oil pressure sending unit is tapped directly into the block, leaving no chance of a leak unless it was coming from the unit itself. Colder, thicker oil is harder for the engine to pump so without knowing the weight this appears to be a consideration. My recommendation would be to change the oil to a viscosity that is suitable for your climate,and knowing it is fresh, and call it good.
What about internal oil galleries? I once had a Ford 5.0L block come from the shop with all the screw-in plugs installed but they left out an internal pressed-in plug and I had to pull the engine apart to find it.
Basic troubleshooting - If it used to work fine and now it doesn’t, the problem isn’t in a factory assembly error made 10 years & 200K miles ago. It is something recent.
Sounds to me like a perfectly healthy car which sat in the cold with summer weight oil, coupled with a driver unused to typical below-freezing starts.
I have the complete schematics available for this engine. All other oil galleys are to provide pressure to the crank, cam, etc. I see no internal plugs other than four that block the casting holes in the head that would also be sealed by the head gaskets. If they were leaking they would either leak into the cylinder bores or back into the return holes to the pan. As the engine hasn’t been out of the vehicle recently I don’t really see this as a possibility. Either way, if they were missing it would be burning oil or have no pressure to the rocker assemblies. Severe valve train noise or plug fouling would be the result.
Actually, I topped it off with about 13 gallons yesterday. I replaced the battery two or three years ago.