4.0 OHV Maintenance Suggestions

Looking for some maintenance/replacement suggestions on a 1994 4.0 OHV with 150k miles on the clock.

For a 21 year old engine, it still runs incredibly smooth. Even with 4.56s and 33's I get 17-18mpg on the highway so i'm thinking it's running pretty efficiently, however i'm concerned of things that should be proactively replaced at this age before failure.

Nothing major has been replaced over the years, standard fare stuff: alternator, starter, valve covers/gaskets, pulleys/tensioner,t-stat, etc.

First thing that comes to mind is radiator/other cooling related parts. Not loosing any coolant, however 21 years is a while for stock parts.

Any thoughts as to weak areas I should be giving attention that could blow up on me one day soon with this age?

Be on the lookout for intake manifold gasket leaks. The upper gaskets would cause a vacuum leak and throw some lean codes at worst. But the lower gaskets can allow coolant to seep into the oil, since our engines have the thermostat housing concurrent with the lower intake manifold. Even the lower manifold bolts themselves have been known to back off slightly, so it wouldn't hurt to re-torque them if you have the opportunity. Ethylene glycol is a killer on bearings.

And clean that manifold while you're at it. Same with the EGR tract (don't remember for sure if 94s had EGR).

Fortunately, reports from rebuild units at 300,000+ miles seem to show that the timing chain is quite robust and will last virtually forever, especially compared to the SOHC version.

With the right care, our 4.0L OHV V6s will just keep running and running.

Excellent, appreciate the info!