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Comments at Best Motor Oil - JeepForum.com|
I run Valvoline 10w-30. Definitely look at the oil filter you use. From what I have researched, I'd say stay away from Pennzoil, STP, Fram, and Quaker State filters. Bosch ones are pretty good and so are ones made by Purolator sold under other brand names.
As for oil, really it is all the same except for maybe additives that claim whatever. As long as you change it every 3k (which a lot of people disagree with), you can run whatever oil you want really. I prefer to stick with well known brands myself.
Comments at Oil filter 97 wrangler tj - Jeep Wrangler Forum
No FRAM should ever be put in or on a Vehicle. Find a WIX, Mobil, K&N anything but a FRAM.
Purolator PureOnes and Fram Tough Guards
I also like the over sized filters since they are the exact same filter just 40% larger which is great since it adds more surface area for oil to pass threw and wont build up too much pressure as easily and go into by pass mode (like when oil is cold and thick) also since it is bigger it holds more junk before getting clogged up. best part is they are the same price as the regular sized filter. I know not every jeep has room for the filter but in my experience every 4.0 TJ does.
Comments at Synthetic oil in long stroke motors
I agree with these statements wholeheartedly. My opinion is that if you have an old engine that has not been rebuilt recently or even rebuilt at all I would not use synthetic oils in it. Here's a short story to back up that opinion. I have a 1998 Jeep Wrangler. When I bought it, it had around 90,000 miles on it and it was running strong with absolutely no leaks. After owning it for awhile, I decided to start using synthetic oils in it because I had heard they performed better which is probably true. However, a short time later I developed an oil leak. As the miles added up and time went by the leak slowly became worse until finally I was at the point that I had to add oil at every gas fill up. Eventually, I began to hear a clunking noise in the lower end of the engine. Long story short, it was a spun bearing that resulted from continually running with an insufficient oil level due to the constant leak. Now the Jeep is sitting in my yard immobile and collecting dust. The synthetic oil found the pre-existing holes in my seals and seemed to make them worse with time. But I'm not totally against synthetics. I just think they should only be used in a newly rebuilt engine and NEVER in an old engine. On a side note, when I took the engine apart looking for the cause of the noise everything was squeaky clean. Not a bit of crud or sludge anywhere. That synthetic oil really keeps the engine clean
Comments at Car Bibles : The Engine Oil Bible
Comments at Is Synthetic Oil Bad for Old Engines? - Car Talk