2001 Jeep Grand Cherokee Jeep Grand Cherokee

If there's a rod knock, the bearings have been damaged and the resulting low oil pressure is going to do much more damage if you keep trying to force it to run. The engine already needs to be totally rebuilt but some of the internal parts may still be salvageable. For sure the crankshaft and connecting rod bearings are gone. Over the course of a few miles driving it like that, some of the connecting rods will get hammered out and will need to be replaced. With no oil pressure, no oil sprayed onto the cylinder walls to keep the pistons lubricated. They will be scuffed and the cylinder walls will be scored. The cylinders will need to be bored oversize and new pistons and piston rings will be needed. Almost certainly the crankshaft will need to be machined or replaced. Camshaft lobes are very sensitive to lack of lubrication so most likely it and the lifters will need to be replaced.

It will probably be less expensive and faster to find a good used engine from a salvage yard. Many of the larger ones can install it for you too.

Hold the phone. I'm only going by what you've posted so far. If the oil pressure is good, it is doubtful a bearing has "spun", meaning it is destroyed. One of those will be the first thing to go when serious damage occurs. With good oil pressure, most likely you are not hearing a connecting rod knock. That is pretty loud, and people in the parking lot will run to get out of your way when they hear you coming. If you're hearing a light ticking up higher in the engine, that is likely the valve lifters that have bled down from lack of oil. That is relatively minor and will go away on its own. At the mileage you listed, it's not uncommon for a lifter to be reluctant to pump up with oil right away. I had an old car that had one lifter that always took at least 30 miles to quiet down after every oil change, then it was fine until the next oil change.

Before we assume you need a different engine or a rebuild, have a mechanic listen to any noises that are still there. A collapsed lifter sounds a whole lot different than a rod knock.

Sorry to leave you hanging for so long. I'm fighting a dying computer that is on its last legs.

Do a cylinder leakage test first before you condemn the engine. If the rings are not sealing, you'll hear the air escaping at the oil cap or dipstick tube.

White smoke IS a sign of a leaking cylinder head gasket, but only when it comes out of the tail pipe. Something else is going on when you see smoke under the hood. A hose or gasket likely has a small leak and the coolant is puddling somewhere, and burning off when it gets hot. The obvious clue is the coolant level will be going down in the reservoir. If it is, a cooling system pressure test may identify the source of the leak. If it doesn't, you can add a small bottle of dark purple dye to the coolant, then check a few days later with a black light. The dye will show up as a bright yellow stain that you can follow back to the source. If you see the dye inside the tail pipe, suspect a leaking cylinder head gasket, but that's not common on that engine.