Jeep 4.0 I-6 Question

Last night I parked the Jeep ('05 Wrangler, 4.0 Inline 6, OEM EFI) at a friends driveway, slight uphill slope. I parked it in either low or second, and didn't set the brake. When I came out about four hours later the Jeep had rolled backwards about ten feet, which would have rotated the engine backwards several revolutions. When I started the engine it knocked something fierce - sounded like every lifter was drained back. I shut it off, re-started and it was the same, but seemed to lessen with RPM's a little. Drove home, about six miles, and it was idling quietly when I pulled into the garage, fully warmed up. This morning it was fine, starting quickly and idling normally.

I'm scratching my head why a few rotations backwards might cause this. Any thoughts, ideas or experience to explain it? I'm not worried about it, but wondering about cause & effect.

HMmmm... interesting! I'm also curious as to what replies might come through. I can't imagine what may have happened.

Could it have rolled back far enough that the oil pump, while turning backwards, pumped all the oil out of the pump, pickup, and tube, then when you started it you had a bit of cavitation to overcome??

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Originally Posted by Dave Severson

Could it have rolled back far enough that the oil pump, while turning backwards, pumped all the oil out of the pump, pickup, and tube, then when you started it you had a bit of cavitation to overcome??

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I had not thought of that and it sounds reasonable, but while it was knocking I looked at the oil pressure gauge and it was normal, if not a bit higher than normal which I attributed to it being cold and me revving it a bit. I've never seen anything like this before.

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Originally Posted by rspears

I had not thought of that and it sounds reasonable, but while it was knocking I looked at the oil pressure gauge and it was normal, if not a bit higher than normal which I attributed to it being cold and me revving it a bit. I've never seen anything like this before.

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So this must not make sense to anyone else, either. It started quiet again this morning, so I guess I'll just chalk it up to a coincidence and remember the date. Earlier in the day I had swapped out a leaky radiator, put on all new hoses, and changed the oil & filter. Nothing done would lead to lifters leaking down, which I'm assuming is what happened. Oh well.....:HMMM::confused:**)

Roger,
It's a mystery to me, too, but I'm wondering if you are sure the knocking noise came from the motor or if possibly it came from the transmission?

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Originally Posted by Hot Rod Nick

Roger,
It's a mystery to me, too, but I'm wondering if you are sure the knocking noise came from the motor or if possibly it came from the transmission?

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Cannot be. Six speed manual transmission, idling with the clutch dis-engaged (in). It was quite obviously noise with the period proportional to rotating speed (engine).

I would think that 10' would get more than a few revolutions. As said before probably pulled all oil out of pump. being cold would take awhile to get back into system. Where is the oil pick up tube front, rear, center??

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Originally Posted by cffisher

I would think that 10' would get more than a few revolutions. As said before probably pulled all oil out of pump. being cold would take awhile to get back into system. Where is the oil pick up tube front, rear, center??

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Sump is in the rear. You & DaveS may have the answer. If it was parked in low ten feet would have spun the engine 19+ revolutions, and if in second 13+ given the 33's and the rear & tranny ratios. If it pushed all the oil out of the pump & pickup then the lifters would have lost prime on crank, and would have been running empty for a bit even when pressure was back with the cold oil.

The oil pump more then likely lost it's prime, takes awhile to get the pickup tube, pump, and all the oil galley's packed full of oil and all the air out of the system.......Same thing happens in circle burnin' when you spin out and don't get the thing out of gear quick enough,,,,even seen a couple engines lock up after a spin when they push them off if the driver hits the ignition switch to soon. Another one of them learning things, I guess.

Thanks fellows, I learned something here. :3dSMILE:

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Originally Posted by techinspector1

Thanks fellows, I learned something here. :3dSMILE:

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Just more of the story of my circle burnin' career, Richard!!!! They never put a part on them there Sprint Cars that I couldn't break!!!!!!!!:whacked::LOL::LOL::LOL: