Ok, I know the 100 deg. Texas temps aren't helping but I'm having a bit of an anomaly with my coolant system. Every other time or so when I drive my 06 rx around town (stop n go) traffic. My temp gauge rises significantly. It's never redlined or spiked out at top of temp gauge. Straight (hwy driving) doesn't really seem to be an issue. Temp seems to stay normal then. When I get home after driving around town, I check and the hood and the coolant is either boiling or evaporated. I've also seen the coolant leak out, but I'm pretty sure it's coming from resevoir overflow. Also, there seems to be some coolant splatter on the engine cover. Every so often. Any clue what this could be? What would be symptoms of radiator cap problem vs thermostat vs cooling fan failure? Or anything else for that matter. Oh yeah, whatever the issue, it seems to be effexcting my a/c system. It's hard to keep cabin cool while doing stop and go but when moving and temp falls, a/c seems to cool better again. W-t-f? any thought?

 

liquids shouldn't boil under pressure (i think). so, if you see boiling, that likely means you may have a small leak somewhere....i think...

 

check your coolant overflow bottle AKA the plastic see-thru tank.

the plastic tab where it locks your coolant cap in place, it might got brittle and cracked, and is not holding the pressure correctly.

or you might have a leak somewhere else, check

and at places like Texas, you can use higher distilled water count vs EG. 30/70 should do. 30 EG 70% distilled water.

 

I am having the EXACT same problem, word for word.... is your auto or stick??

 

the radiator has a plastic cover. the little pipe on it might be broken and not holding pressure.

 

I had the same thing happen to me but started doing that after i got the engine replacement. It turns out one of the lines had a small little crack nxt to the clamp, of course i had to rev all the way to 9gs to find it.....

 

Mine is a stick - 6speed.