My 1998 sr5, 180k- started to overheat about 2 weeks ago in traffic.
I had my AC on, and I smelt coolant so I pulled over and it was boiling over the overflow.

I replaced the fan clutch, as I checked this forum and it was a common suggestion (OEM Asin model). I drove the car all week and had no problem, even with AC on. Friday I drove it home 45 minutes, 1/2 of this in traffic. Right when I pulled into my driveway, I noticed the temp gauge heading upward, poped the hood and coolant was starting to overflow again.
I've never let it get into the red on the temp guage.

What would you guys do next?

New parts I've already changed in last 2 years:
-radiator (preventative)
-radiator cap
-fan clutch
-upper rad hose
-alternator

*My mechanic told me I need a pinion bearing soon, it is making noise, but there is no play in it. Not sure if this is relevant.

*May be unrelated, but the only other time I've started to get hot is on this one trail that I've been up. There is a steep section and every time I get to it (about 1 mile in) I see the gauge start to rise. This happened a few times about a year ago, my solution- I just stopped hitting this part of the trail, and never had an overheating problem until just the other day with AC on.

Thanks!

 

A good burping?

 

Dirt in the condenser blocking air flow to the radiator when your not moving??

Was your old fan clutch bad??

Maybe the one you swapped in is not working like it should??

 

Pressure test. New thermostat, flush, good burping.

 

Thanks for the advice guys, I'm going to throw a thermostat in next chance I get, and I'll try and burp the system today.

I'll also take a close look at the condenser and see if it can be cleaned out a bit.

 

The only thing you haven't mentioned changing is the water pump. I bought an 88 automatic pickup from a neighbor that had the same symptoms as yours. Everything in the cooling system had been changed and flushed. It turned out that even though the water pump didn't leak the blades on the impeller were worn to the point that they didn't pump at low RPMs.
Replaced the pump with a new OEM and on a 100 degree day with the AC on it runs at 190 degrees.

 

It is quite more involved to change a water pump on a 3.4 you don`t mention what your 88 was.

If your going to the water Pump you may as well do the Timing Belt