Low Mileage Wrangler 4.0

Mar 6, 2021
Good day BITOG’ers, my family just got their hands on a 04 wrangler 4.0 with only 36,000 miles. My question to you is should we stick with conventional/synthetic blends or go to full synthetic. I’m going to keep running 10w30 in it but in worried about seal leak if we switch to full synthetic. Is my concern valid? Thanks
Either will work fine. The 4.0 leaks regardless of what is in it. :LOL: But seriously a synthetic won't make it leak anymore than it probably already is. Whether or not a synthetic is beneficial to you really depends on how long you expect to run the oil. Mine sees very low mileage and I change it once a year, so a synthetic would really just be a waste of money.
run whatever you want, the rear mail seal will eventually leak no matter what.

Synthetics will not cause leaks. That has not been an issue for 25 years, but the rumor keeps hanging around.
What can happen is you may have a seal that is already leaking but not leaking badly due to buildup, and the buildup can be cleaned up by synthetic and cause the leak to become worse.
ok, thanks fellas, going to run PYB probably since I plan on doing 3K/12 month OCI's for them since its not a DD.
For years on here , the Pennzoil conventional 10w-30 returned the best results on these engines.

However, these engines do not care. They thrive on the cheapest 10w-30 you can get.
It’s always been PYB in the 4.0 Cherokees I have serviced. 10w30 in mine as it was a back road/hunting rig with few starts but ran for hours once started and 5w30 in my mom’s as it was a frequently short tripped daily driver.
Besides Mobil 1, I've always used any cheap or available xW30/40 in mine. I'd never extend oil changes for mine because my 4.0 can lose half to a quart every 5K miles. For whatever reason it lost almost 1.5 quarts in 3K miles when using QS full syn a few years ago that didn't happen with other synthetic labeled oils like Super Tech and Castrol Magnatec.

RMS on mine leaked for years until it got annoying enough that I changed it. Now 6 years later, it's dripping again. It's currently on Quaker State HM 10W30 for the last 4.5K miles and it drips more than when it was on Pennzoil HM 10W40. It's on track to lose more than 1.5 qts when it hits 5K on this oil. Going to try 5W30 Maxlife soon before I buy another RMS.

Good engine though, and you've got a good model year.