still running hot...

well i posted a couple months ago that my 99 5.3 silverado is running to hot. I tryed a new clutch fan, didnt help, i tryed a new stat, didnt help, there is no crap blocking the rad. I cant figure it out. if i sit at a light for a while, like yesterdya when it was 95* out side, it gets up to about 240*! but when i drive it goes down. When i pop the hood it doesnt feel super hot like youi think it would. Its gotten that hot multiple time and nothing seems to happen. What do ya guys think?

someoine told me to flush the rad... it does ave 130K miles on it.

Water pump?

Blocked or partialy blocked coolant passages in the block/heads, flush.
I had a similar problem and a flush helped, but then I tow alot so a couple of weeks after that I had an old school 4 row brass rad customized to fit and have never had a problem since, even towing a camper and boat through the desert mid day w/ac. hate those plastic rad's.

I fixed my 2001 Silverado two weeks ago. I had the same problem, ran fine at speed but would quickly overheat when idling. Truck has 200k, and has had a slow coolant leak (I never did find out where but suspected the water pump)

I replaced the water pump, thermostat, and radiator hoses. I flushed the whole system. I also replaced the clutch fan (which I also suspect was faulty) with a Flex-a-lite dual electric fan.
I suspect the water pump was the biggest contributor. When I replaced everything I tested the new fan setup by waiting for it to heat up enough to turn the fans on. I had to wait a very long time even idling in 98 degrees, It just stayed right at 203.
Eventually the fan did come on an it has stayed at 203 even idling this past weekend in 103 degree weather.