I have a 1996 Jeep Cherokee xj 4.0 , automatic . 344678 miles. I’ve had it for about 7 months. It is a 4x4. Any issues that are common that I need to be aware of? The head has been reworked. Thank you for any information on the Cherokee XJs you can provide. Should I add a zinc additive with every oil change to help protect the camshaft? I really love your YouTube videos. I hope you are enjoying your move to Tennessee. Thank you
Horace Mangham
In stock form those engines don't have crazy valve spring pressures so an additive is not really needed for a cam that's already broken in. By today's standards they're more like tractor engines than anything else. Of the issues that the 4.0 is commonly prone to, camshaft failure is not among them, it's actually quite rare. However if you want to be sure for peace of mind there are high-zinc oils available as well as additives.
Some of the Jeep guys like to run Rotella T6 diesel oil which has more zinc than standard gasoline engine oils. For that matter most of the major oil companies make specialty oils with high zinc levels aimed mainly at classic performance cars. (The 4.0 is based on a 1964 Rambler engine and really is not very fussy about what oil is used in it.) I haven't done anything special for my '99 Cherokee and there have been no problems.
For starters, here's chart showing zinc and phosphorous levels in Mobil 1 products:
