Overheating Issue Any thoughts plz???

I have a 2002 ls 3.9l v8.


Here is wats happening, it is still about fairly chill outside so i let the car warm up or i usually drive slow for a few mins an gradually build speed after about 7-10mins. if i do this the car use to not overheat as often. however if i notice the temp guage rising i would turn on the heat/ac to about 78 degrees on full blown this would normally cause the temp guage to decline back to the half way mark. most of the time that works n i can continue driving. one time my temp peaked past the high point n i was tryning to pull over when i noticed it started to come back down on its own. well yesterday it peaked at the highest point again and so i tried to pull over then the cpu read "engine power reduced..." my car had been feeling a bit sluggish the past two days as well. well ever since the peak my car now over heats more then once per drive when i use to be able to solve it by ac and move on. well the ac "trick" still works to some extent but its clear this issue needs to be looked at soon.

when it overheats i notice that under the hood the smoke seems to come from the right side of the engine. i also use to smell oil burning a few weeks back.

my problem is this i have browsed this forum before asking for help and have noticed the issue of valve cover gaskets and read up on leaks and seeps and the dealer ship told me back in january that i had a hole or crack in the vc gasket but no leak. of course eventually it would leak but how come the ac brings the temp gauge back dwn if myengine is overheating?

does anyone have an opinion as to what could be the problem. vc gasket? head gasket? plugged up thermostat?

the radiator fan works and again was also flushed out.

thanks in advance.

The heater would bring the temperature down because you were using the heater core and blower motor as an auxilliary radiator, radiating heat from the cooling system via the heater core.

When the A/C is turned on, the hydraulic cooling fan pump should enable the cooling fan to run.

Have the fins of the radiator and A/C condensor been inspected for debris and bent fins? If either are obstructed, there will not be sufficient airflow to properly cool the engine.

Also, consider having the system and cap pressure tested to make sure the cooling system is being properly pressurized. The system needs the proper amount of pressure to keep the boilover (and freezing) protection in spec.

Yes, if the thermostat is stuck closed, it could cause the engine to overheat as well.

The Cylinder Head Temperature (CHT) sensor is what triggers the engine to run in reduced power mode. When the CHT registers a head temperture above 250 degrees F it turns off the fuel injectors for half of the cylinders and uses those cylinders as heat pumps to help cool the engine.

-Rod

great info i appreciate all that very much. yes the radiator was flushed but i have noticed it has bent fins i will look into all that was listed. thank you

Rod, I just read your response to the question above. My car overheated and I had the collant fluid container replaced because it busted. Two weeks later, the car ran hot again but I did not loose any fluids this time. My mechanic put in a thermastat, a week and 1/2 later, my temp gage started to go up but not in the red, I took it back and a code 1285 came up which was the temp overheat sensor, had that replaced. Now I can't get the gage to stop going up close to the red zone, I did notice that when I turn the ac on, it is blowing warm air when the gage is up but when the gage start to comedown, the air gets colder. What is going on? I need help, I'm spending too much money on this car

Welcome to the forum!

What year is your LS, and which engine does it have?

The code 1285 is "Cylinder Head Over Temperature Sensed" and would not necessarily indicate that the sensor itself is faulty. There are other codes for an out of range sensor or open/shorted sensor.

According to the service manual, items to check for the code 1285 are:

Low engine coolant level
Base engine concerns
Engine cooling system concerns
CHT sensor concernI would add to this list a faulty pressure cap and air pocket in the cooling system. Since you've had your system open recently, the air pocket would be high on my list of items to check early. If your mechanic has a cooling system pressure tester, have him test the pressure cap too.

According to the service manual, "On some applications when this fault occurs, the Engine Temperature warning indicator will illuminate and/or force the temperature gauge to full H (Hot) zone by grounding the engine temperature warning circuit."

I'd suggest you get the overtemp condition remedied first, then worry about the A/C issue. I suspect fixing the cooling system will also allow the A/C to work properly. When the LS overheats, the engine is supposed to go into "heat pump" mode and as part of this, probably disables unneeded power-robbing accessories such as the A/C compressor.

-Rod

I had the same problem with the overheat and not cool air blowing. It was my heater control valve about $140 fix and easy to do yourself. Its attached at the cooling fan and has 3 hoses going into it. Its right under the condensor. Takes about an hour to do. good luck