Not to get in a pissing contest, but the previous film of oil will prevent crank scoring on a NORMAL low rpm startup. ANY metal to metal contact in an engine RUINS the bearings right THEN, it is not cumulative damage it is IMMEDIATE. This noise everyone is complaining about is not because of a Jeep design problem, it is CRAPPY quality OIL FILTERS. Half the vehicles on the road have horizontal filters, thats why every filter has a drainback valve. The clattering on startup is noticable because not only does the oil lubricate, it also has a cushioning effect, that's why the reciprocating mass of the lower end quiets down when full oil pressure is achieved. The old vehicles' cam bearings would wear out, causing the upper end of the engines to go ''dry''. The cam bearings instead of lubing and then the oil being pumped on up top to the rocker arms, would wear so bad that the oil would spray out the edges of the cam bearings, giving an engine that had great oil pressure at the crankshaft, but NONE up top. The bottom of the engine wouldn't make a peep, but the top sounded like a thrashing machine. You could go to an auto parts store, for 3 bucks get an overhead oiler kit, tap a ''t'' from the sending unit and bypass the cam bearings. Run a copper line up to a hole drilled thrun the valve cover and run the line into the rocker arm shaft- instant oil pressure. Even though 1/2 of the engine had no oil pressure it would run FOREVER on the FILM of oil. Whether the film is .0001 th of an inch thick or a 1/4'' thick only the surface of the bearing and bearing journal is lubricated, the rest functions as ''cushion.''....

 

The noise on startup is NOT coming from metal to metal contact. TINMAN is correct. The noise is coming from lack of oil pressure, not metal to metal contact. There is enough of an oil film to protect against any metal to metal contact. An oil film will last a VERY long time, especially with today's modern lubricants. When I worked at the local Benz dealership, we used a product called Motor Honey to assemble engines. Anyone familiar with this stuff, knows it has a viscosity similar to chainsaw bar and chain oil. It just doesn't go away. I've continued using Motor Honey through the years and had great success with it. Damage from metal to metal contact would result in having a permanant noise....even WITH oil pressure. All that is happening is oil is draining out of the oil filter's faulty anti-drain back valve back into the pan. Once the engine is started, it has to refill the filter, BEFORE the pressurized oil gets to the bearings. It is in this instant, that the noise is occurring. I will say this.....synthetic oils sometimes exhibit this problem moreso than conventional oils because of their increased flow characteristics. Synthetics just flow so damn good that they can sometimes defeat an otherwise good anti-drain back valve. I just live by the K.I.S.S. rule. Since the Jeep did NOT come from the factory with synthetic oil, I leave well enough alone and do not run it.

 

5 quarts? I thought it was 6 quarts for an oil change?

 

It is 6 quarts.

 

I think this may be a major factor that we need to be looking at, I know I had absolutely no issues with the dino oil and Mopar filters for the first three oil changes. When I went to Mobile 1 synth oil and filter the trouble started. I swapped in a Mopar filter with major improvement, but I've been trying to determine if I am getting a split second of clatter now even with the Mopar filter (synth oil). Interesting.

 

so heres a question can I go back to conventional oil from the synthetic that I have in there now, I have heard that you can't switch back

 

You certainly can.

 

how do you know if you're having a dry start?

 

You will hear the engine make a clattering noise when you first start it especially after ater sitting for a while.

 

Jack, the best way to tell is after your Jeep has been sitting a day or two. Get in and turn the ignition to the "ON" position. Let all the lights cycle off. Make sure accessories like the radio and A/C are all off so you can hear. While watching the oil light and listening to the engine, start it up. If the oil light comes back on, even for an instant, chances are your anti-drain back valve in the oil filter is not working properly. In some cases, as outlined in this thread, you can even hear the rod bearings clatter for a split second on startup. So far, I've found that WIX filters work very well. Others have had luck with other brands. I don't think there is one filter in particular that is a sure fire fix. You just kinda have to swap around until you find a good one.