I've got a 89 4wd 22re pickup that is overheating when climbing steep grades or in stop and go traffic on very hot days. Otherwise it runs at a steady SOT at idle or at highway speeds. I've replaced the radiator and coolant 1.5 years ago, recently flushed the radiator and burped the air (though it didn't seem like much air came out). I tested the t-stat which seems to be operating fine. Next on the list is to check the fan clutch and maybe trouble shoot the water pump(?) though it doesn't look coolant. It seems like the overheating issue has gotten worse since I replaced the radiator and I'm wondering if it might be related to the fact that I used an inexpensive aftermarket replacement instead of an OEM part. A little reading around made it sound like cheap radiator don't work well enough to cool the engine under exertion. Any opinions or advice to things to check before doing more drastic replacements such as a new water pump or another, better new radiator is much appreciated.

 

Why did you replace the prior radiator?
Is the current rad leaking? Have you pressure tested it? What about the cap?
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I replaced the original radiator because it was very corroded and leaking. There are no leaks in my cooling system currently. I have not pressure tested the radiator, I assume its fine since its almost new and has no leaks. The cap is also in good condition and seems to provide a good seal.

 

Fan clutch: resistance when the engine is cold, no play in the bearings. After the engine warms up, the fan is easily stopped by a few leafs of folded paper. When I rev the throttle, the fan does speed up a bit, but not much. When I shut the engine off and spin the fan there is almost no resistance.

From what I've read, these are symptoms of a failing fan clutch, which would explain the over heating under exertion and idling in traffic on hot days.

I'm not certain about my water pump though. I tried looking for coolant flow through the radiator filler neck and it seems like once the thermostat opens there is a gentle swirling of coolant in the radiator, should the flow be more obvious than that? I know the pump was replaced in 2010 with a toyota part when the engine was rebuilt so I know its not that old.

 

That does sound like a bad fan clutch. Since the swap out is fairly simple I would go with that first. Given what you wrote the water pump doesn't seem likely.