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I was also wondering if i can use full synthetic oil on my 4.0 lj do i get better preformance out of full synthetic oil or there is no point. thank you. :cool:
 

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In my experience you can go longer between oil changes, but the filter still needs to be changed at the normal intervals. I usually do mine at 3k to 4k miles. The oil I use is rated for much more but the filters still get saturated at around 3 or 4. If the filter goes into bypass it does nothing for the oil. I know when I was a teen, and a oil jockey, there was a company doing an experiment on a truck with synthetic. They ran 150k miles on that truck. They never changed the oil only the filter and added the amount lost from changing the filter. They always brought the truck into the shop I worked at for the filter change at 3k miles. When the engine tear down was complete after the experiement was done there was normal wear but nothing like would be in an engine with that many mile on it. I dont recommend going this long long without changing the oil, but seeing it with my own eyes convinced me to start using synthetic when I was able to afford it on a regular basis. As far as actual increases engine performance, I dont notice a difference but maybe someone else here has. I hope I made sense when typing this:)

Odhinn
 

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Synthetics and mineral-based lubes absorb contaminants like combustion byproducts, acids, etc. at the same rates. And those contaminants cannot be filtered out by a conventional oil filter. So while the synthetic oil itself may last longer, it still absorbs contaminants at the same rate that mineral-based oil does which can only be removed by changing the oil.

So the hype about a synthetic oil being able to go longer before being changed is simply a myth. Change the oil and filter together at the recommended and reasonable intervals and your engine will be well protected, synthetic or mineral-based.

Only in extremely cold conditions is a synthetic oil worth it's weight in gold due to its better flow abilities when very cold. :)
 

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I've used Mobil-1 Fully Synthetic oil the last couple of oil changes in my 02 TJ. I really haven't noticed much of any performance change vs. the conventional oil I used before but I have read that it holds up better. They have pretty comparable prices at Wal-mart if you buy the 5 quart jug.
 
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