So when I first got my truck, it would overheat pretty badly. I found the fan clutch to be worn out, and replaced it with the cheapest one I could find from Oreilly auto parts. That was about two years ago, and it dramatically improved the overheating. On hot days, it still tends to overheat if it idles too much. Freeway speeds are generally okay. But if I have to sit through any traffic after the freeway, the temp keeps climbing.

I just tuned it up and timing and idle RPM are set properly. I did a compression test and got almost exactly 185 across all four cylinders. I didn't check the valve gaps but based on the compression test I'm assuming they're fine. I also put in a new thermostat and spark plugs.

So, the only thing I can think of to improve cooling is a "better" fan clutch. I have seen "severe duty" fan clutches for about $100 as opposed to the $40 one I put in before. Should this do the trick? Or is there something else I'm missing that could be causing the overheating?

 

Clogged radiator most likely.

 

I agree, most likely a radiator issue.
I won't rule out bad rad hoses though, particularly the lower one.
If the inner lining is separating, the internal diameter of the lower hose will shrink,
reducing the amount of cool coolant able to get from the rad to the water pump.

For visualization: imagine a fire truck connected to the hydrant. If the hose is 3" diameter all the way there's good flow. Now, if that 3" hose was reduced to 1", how much water is going to flow?

Like I said though, it's probably the radiator, but the hoses need checked and replaced too.

 

Do you still have a shroud on it? if you do then most likely your radiator isn't up to par. Usually if you have a plugged radiator it will get hot at freeway speeds though.

 

Have you or any previous owner used a cooling system stop leak in it? that stuff is known to clog up everything cooling related