For the 4 years my compressor was broken, my engine temp NEVER moved above that "just below half" mark. I finally got compressor replaced (2 years ago) and on really hot days, I just can't use the AC unless I"m on the highway. I've been digging around the net and these forums, but I really haven't found someone with the exact same problem. Basically, on hot days (over 75 degrees) if I use my AC, it works okay if my car is moving. If I spend a lot of time in slow moving traffic or stop & go traffic or hit a bunch of red lights, I notice the air blowing from the vents starts to go from cold to ambient temp to warm (today I noticed a slight hissing noise as this was happening). When this occurs, I notice the engine temp is also rising from its "just under half" spot. It will get as high as 4/5 of the gauge, and then start slowing coming back down. I have turned off the AC at this point so I'm not sure if the temp will drop while the AC is still on.

I've checked the fans - both work and both come on when the AC is on. Compressor side fan was replaced recently and works really well. Driver side fan works but doesn't seem to move as much air as the new one. I've changed my coolant twice - most recently about a month ago when I changed my timing belt and water pump. I really wish I remembered to do the thermostat as well at the time. I've bled/burped the coolant (per the manual's instructions). Both coolant hoses get really hot (one slightly less hot).

I plan on checking the pressure in the radiator/cap (I've heard autozone has a tool they lend you?). Other than replacing the thermostat and paying to have my compressor's high/low pressure checked, what else could be the culprit? Radiator? I've spent a bunch on the car already so I'd like to start with the more cost-effective solutions first.

 

if the fans are working correctly= proceed to `install new thermostat`

get a new rad cap while you are at the parts store

observe flow thru radiator at idle and with throttle at 2000 rpm
with a new pump is shuld be moving fast and furious IF the rad is clean
unusual to have a rad prob in our car- unless you went past the coolants real lifetime

 

with the ac off, the driver side fan comes on and off when sitting at a light?

 

My TL recently acted exactly the same. First "hot" day of the year (80 degrees or so), we were sitting in a parking lot waiting to leave from a concert. Kick on the A/C and at idle it was blowing warm. Above idle it was better, but the engine temp was rising too (just like you....well above the normal 2 ticks below halfway)

Turned out our car was low on coolant. I replaced whatever I could: drained existing coolant (including the engine block drain), replaced hoses, t-stat, added new coolant and "burped" per service manual procedure.

While it hasnt been that hot out since (I hate the weather in the northeast!), Ive parked the car and let it idle for up to 15 minutes and it just stays at 2 or 3 ticks below halfway on the temp gauge.

In a nutshell, change your coolant and t-stat while you're at it. Make sure you follow the procedure that is listed here somewhere. Open the heater before shutting the car down and draining the coolant, etc.

 

I'll double check this - I know one of the fans stays on for 5-15 mins after I park during a hot day and moderate drive, I'm assuming it's the driver side. 01tl - how do I observe the flow?

Chris - thanks for the info, I'll look into changing the hoses and the coolant when I change the T-stat. I'll dig around for the post you are talking about.

 

So if my fan temp sensor is bad, the fan should stay on for 5-15 mins after I turn off the car EVERYTIME? It only does it after really hot days - could it still be a fan sensor thing or is it just keeping the fan on because I have another problem that is running the engine/coolant hotter than normal?

 

sounds like fan temp sensor A to me,,based on many others reports of similar problem
It will appear the fans work when you look- but in the course of driving the driver side/main cooling fan stops working
then it runs way too long after shutdown
The key is that long run time,, usually indicates bad fan temp sensor

replace that sensor,,99s located on top at thermostat
00 and later on lower rear pass side corner of rad, unscrews to remove,,easy diy
aftermarket part ok

 

Thanks! I'll start with that then try the thermostat if that doesn't fix it.

 

I just checked the location, will I have to drain the coolant to replace the sensor? If so, I might as well just change the thermostat too.

 

no- just be ready with the new sensor- unscrew- replace- tighten gently
Leave rad cap ON and engine cold when you do this
that will keep the fluid from rushing out