My friend has a 93 Jeep Cherokee. It's overheating when he goes up a hill. Runs fine for a while, then overheats.
Thermostat has been replaced, and the fan clutch seems to be ok.
Any ideas, y'all?

Thanks

Might be in need of a decoke?
Carbon build up on the cylinder head/ Piston crowns
Too much and the engine "runs on" after switching off The carbon starts to burn and any surplus fuel vapor is ignited causing a dieseling effect (sounds aweful! )
To inspect Take a spark plug out, turn the engine over until you can see the Piston at or near the top of the stroke ,may need a flashlight shining down the plug hole? Get a pencil or a small blunt piece of wood, scrape it gently along the surface of the piston and if it feels smooth the problem lies elsewhere.
If it feels very rough then a decoke Is a good Idea. It is the same thing as doing a defrag on a computer Improves reliability and performance also fuel consumption will improve slightly.
And when it is back on the road a drop of Redex in the Fuel tank every other fillup will help keep the coke build up to a minimum
The job itself will take about 2-3 hours and it's not for the non mechanically minded If your friend has the cash book it into a garage and buy the (top end)gasket set about $20? otherwise The garage will invent a number and add it to the Labor charge they will source the same or cheaper gaskets at a trade discount ,I should know this because my Brother in law is a Manager at a garage,I'm wise to this scam
Good tip find out first what their Labor charge is per hour? And ask if they'll do the job "Labor only" and you supply the parts. And you want to see the old parts when they are finished,Good mechanics will do this for you,may even let you see what's going on?

Could also be a restricted radiator due to scale. You could try a thorough flushing (with the engine running and until the water runs absolutely clear). If that doesn't do the trick, a trip to a radiator shop may be your only recourse.

It would also be a good idea to check the cooling fins on the radiator. They may be bent or clogged with dirt, bugs, etc. If they are bent, you can buy a "comb" at your local parts store which will straighten the fins.

Thanks, y'all....I passed this along to Mr. Skeptical.