Taking my 2004 , showing 117,000 miles, to a 2nd shop tomorrow for tests and recommendation. 1st shop gave me an estimate to replace both valve cover gaskets and both head gaskets because of coolant leak and oil leak. What is the history of the valves, seats, etc. on this model engine? I don't have money to burn, but if I'm looking at a valve job of several hundred dollars in 2-3 years, I might as well bite the bullet now. Now that's a tough call, but easier made if the 4.0L is prone to valve problems. Are there any other seals, gaskets that need replacing while everything is apart? These shops should know better than I about work necessary, but I want to be prepared.

 

Check PCV system if valve covers are leaking oil

4.0l SOHC engine was not known for head gasket or valve issues, just timing chain issues from 1997 to 2003, which can be corrected

If you have to take heads off then machine shop can check valve condition at that time, unless engine was running lean and over heating ALOT there should be no valve issues under 300k miles

Intake valves rarely have any problems at all they are cooled by incoming air:fuel mix

Exhaust valves are what wear out because of the heat, if a cylinder runs too hot, lean or pinging/knocking then exhaust valve can warp a bit and during cylinder ignition some of the explosive force can escape through the gap between valve and seat, this eats away at the valve and the seat.
Or a valve guide can start to wear out and stop the exhaust valve from spinning, both valves spin a bit each time they are opened, this spinning prevents wear at a single point on the valve and seat, if an exhaust valve stops spinning then it will get a "hot spot" and warp
Either of the above cause a "burnt valve", always an exhaust valve, and then that cylinder loses compression and misfires

 

Thank you so much!