I just bought a 2006 TJ with a 4.0 that has 69k miles on it. It looks like it was treated pretty well but I don't know what kind of oil the former owner used.
I personally want to use synthetic. Any issues with just going to straight synthetic or should I do a blend first, or something else?
As far as I know, the former owner may have used synthetic.
Also, I bought some Autolight iridium plugs for it, anyone use those? What are your thoughts?
You can switch to or away from synthetic engine oil at any point and at any mileage. You can even mix synthetic and conventional engine oils together. Personally I won't pay extra to run synthetic unless I'm in the dead of winter in an uber-cold location where synthetic is worth it but that's just me.
Autolite's XP-985 Iridium plug is a superb plug and a very good choice. Apply a dab of antiseize to the threads (keep it away from the electrodes) to make sure they don't stick in place since they'll be there a long time. An Autolite rep I know said he pulled his Iridiums at 165K miles to check on them and there was no detectable gap/electrode erosion or wear on them. Iridiums are the best performing and longest lasting plugs I am aware of.
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I ran synthetic in my old Ranger for the 11 years that I had it, truck never failed me. I drove it out 2 hours from home to turn it over to it's new owner Sunday and she ran as good as the day I bought her. Only part outside of plugs, wires, etc that I had to replace in 105k miles was the water pump... so I kind of like the idea of using synthetic. Not saying that she would have done any worse on traditional oil, but she sure as hell did well on it.
As for plugs, I used to push iridium on my customers when I worked at Autozone. I liked them and all of my customers that bought them loved em. I just didn't know how well the Autolights would work in a 4.0, I know some engines are picky about certain plugs... my Ranger almost died when I put Bosch in it one time. They only lasted about three months before I replaced them.
Synthetics are designed for extreme cold weather and high performance engines but are still fine in your Jeep. Me, I buy whatever is on sale (as long as it's API certified), which means fossil fuels, and change it every 4k miles or so. I learned this from my dad who was a diesel mechanic for close to 50 years. Never had an oil related problem in the 37 years I've been driving.
__________________ But the wisdom that is from above is first pure, then peaceable, gentle, and easy to be intreated, full of mercy and good fruits, without partiality, and without hypocrisy. James 3:17 (KJV)
I have been running the synthetic for a while now ----no complaints and I go 5K between oil changes. No valve noise anymore and it SEEMS to run better. Maybe the old placebo effect but it isn't that much more IF you watch and catch it on sale. 150K+ on my '04 TJ.
That is all I use in my vehicles. I use it in my wife's truck because that is our trip vehicle, and I use it in my Mustang and Jeep because they see a lot of high rpms (bad driving habits). You can go back and forth. I like the longer intervals between changes, 5-7000 miles depending on wether I went to the track, mudding, or pulled something a lot. It supposedly does offer better startup protection and better lubrication. I put it in my jeep when I got it with 48000 I think on it and have no leaks. I would probably say it is a waste of money unless you beat on your Jeep.
Synthetic oil is also much better at handling high heat.
If you are running off road with low tire pressure and engine temperatures are rising... synthetic is your friend offering more engine protection.