Oil and OCI recommendations for a 99 Jeep 4.0

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Aug 11, 2004
Ann Arbor, MI
I am going to take over oil changes on my husband's jeep (1999 4.0L Wrangler) and I just wanted another opinion on the OCI and oil I plan on using... I am competent to change the oil and have an understanding of oil weights, but a bit of a novice in the brands/additives/weight discussions. He drives short distances around town occationally and some medium length trips in the nice summer weather. He puts probably 4-6k miles on it in a year and has, prior to now, just stopped into the oil change place when he thinks it's been a while (hopefully averaging 2 changes per year). He's been running whatever 10w30 the oil change places give you. I was thinking to keep using a 10w30 oil, as it seems to be working just fine and thats what the manual says... But, how do I choose a brand? I plan on an OCI of 6 months or 3k miles (whichever comes first) - sound about right? I dont want to pay an arm and a leg, but I am willing to invest a bit in a good oil - we want to keep the jeep going for many many years. Are some oils or oil types better at sitting for weeks at a time? Any suggestions or helpful hints you can think of? Thanks! Erica
I would go with a synthetic like Mobil1 10w30. You will be changing it twice a year so it will set you back about $50 for oil and filter for a very good oil. IMO its worth the extra few dollars you will spend. Daily Drives: -2003 Toyota Tacoma PreRunner XtraCab, 2.7 Liter , Mobil1 Synthetic SS 5W-30. ODO 10000 Miles. -1995 Toyota 4-Runner 3.0 V6, Mobil1 Synthetic SS 10W-30. ODO 91800 Miles. http://community.webshots.com/user/amkeer
Any API certified dino oil would do a fine job with your 2,000 to 3,000 oil change interval, even Wally World $.88 Super Tech. I would recommend a decent filter too. Lots of good things are said about the Wally World Super Tech filter (maybe $2.00 or so). My preference is the top rated Purolator Pure One filter. Good luck and can you give my wife lessons in oil changing?
The Jeep 4.0 likes a 40wt. I'd use a good 5w-40 all year round or a thick 30wt GC 0w-30. German Castrol would be an excellent year round choice. Awesome oil.
I use Mobile 1 10W30 in my 2000 Wrangler 4.0 (62K miles) and my 96 Cherokee (130K miles). I run 5-6K oil change intervals with no problems whatsoever. Used to use K&N filters, but recently switched to Baldwins based on cost vs. quality information found in the oil filter section here.
So should I really just go off the milage numbers when determining the OCI? I guess I'm concerned that the long periods of sitting would somehow be hard on the oil... (I could be way off base, I just dont know!) Mobile 1 would be within budget if it really were better than the alternatives. I use Delvac 1 in my Golf TDI, but I go 10k between changes and that is usually about 9 months. My concern is that I should change the Jeep's oil every 6 months or so just because it has sat long enough. If so, would I be throwing my money away by buying the really nice stuff? I guess my other question is that the manual on the jeep says 3k miles between oil changes if you drive in extreme conditions (which he does, when it's driven), so how do you know if it's ok to stretch that interval to 6k with better oil? I have seen some mention of UOAs and that makes sense. Where does one go to get the oil analysed? Is there an option for determining how used your oil is for those of us without access to a chemistry lab? Thanks for all the helpful advise [Smile]
Erica, the best way to check how your oil is holding up is with a $20-30 Used Oil Analysis (UOA). There is a whole section of them here ... search it using the phrase "4.0" to see other Jeep owner's results. I'd use a 5W-30, 5W-40 or 0W-40 synthetic for the coldest 6 months and then a 15W-40 for the warmer 6 months. Simple and economical. You can get really picky about oil brands, but with a 4.0L Jeep, you don't have to. --- Bror Jace
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