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I currently own a 2002 Jeep Wrangler(4.0 6 cylinder).I am having/had a few problems with it.My Jeep over heated causing the head to crack.I replaced the head with a remanufactured head.I cleaned the rods and took apart the lifters and cleaned them.I clean practically all the sludge that was in the engine.My problem is my oil pressure now.I have no clue on what it causing it to drop to zero and would like some advice or suggestions with my problem.I took out the sending unit and replaced it with a oil pressure gauge(to see if my cluster was bad) and I have changed the pump to a high volume/pressure pump (to see if the the line was bad.)When the engine heats up,the oil pressure drops to zero when at an idle. I drove down the highway and the highest the gauge read was 25-30. On a cold start, the gauge reads about 40,but after running it for 5-10 minutes the pressure drops to zero.Neither changes worked and would like some suggestion or advice to my no oil pressure problem.
Thanks
Katie
 

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I would be concerned about bearings. Rod.main and cam. If you have pressure the oil pump must be working. When the engine heats up and the oil is thins it must no to registering because the bearing tolerance is too large. The only way to be sure is to drop the oil pan and inspect the main and rod bearings. The cam bearing inspection isn't quite as easy. If the crankshaft is scored the engine will have to be pulled and that is the time to check the cam bearings. When the head cracked you really don't know else happened. Just my opinion.
 

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Jeffery is right. If the pressure drops to zero with a new oil pump when hot at idle you have bad main bearings. The good news is that if it isn't knocking yet you can probably get away with just replacing them with new ones. I would do the rod bearings too.

Take the old oil pump apart to see if it is damaged (scoring on the bottom plate or impeller will be obvious) to confirm you had oil starvation or contaminated oil. I wouldn't worry about the cam bearings. Main and Rod bearings with the oil pan gasket will only set you back about $200. If you DIY you are looking at about six hours of work.

Is this a new problem since the overheat? Why did you clean the lifters instead of replacing them? They are only about $5 each.
 
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