I have a 2008 LS3 automatic and in slow traffic with the outside air temp at 103° the water temps start to climb past 230° before I turn the air conditioning off and roll down the windows. The cooling fans are on, and I do have and have tried a couple of 160° stats, and the radiator is not covered up. Moving at 20 to 30 mph does not help.

The 2009 engine has a larger diameter thermostat and housing installed. Does anybody know if this combo will fit and work on a 2008.

 

Since driving at 30 doesn't help, it sounds more like you have airflow restrictions. Try cleaning out any crap in the radiator and condenser fins with air and/or high pressure water spray from the engine side.

A larger stat will not fix your problem.

 

You can't change to the new thermostat without changing the water pump too, which would also necessitate a new upper radiator hose. That's alot of trouble to find out it probably doesn't work.

I agree that it's likely an airflow problem. Something somewhere is obstructing flow, or maybe your fans are not seated properly to get the seal they need to pull enough air through the radiator. With it that hot outside, cooling the engine and pulling the heat from the a/c condenser requires a LOT of air. You're basically pre-heating the air with the a/c before pulling it across the radiator to try to cool the engine coolant.

Although unlikely it could also be air in the cooling system. I know it sounds odd that air in the system would be a situational overheating problem, but I've seen these cars do some weird things like that when only slightly low on coolant.

 

For the most part, the stat only sets the minimum temp.

 

 

You didn't report any unusual temperatures so I wouldn't worry. As you can see in the operational description from the FSM the cooling fan will not even go to high speed operation (with AC off) until the coolant temp reaches 235 degrees. You didn't mention your oil temps which in my opinion are more important. In most other cars you can't read the coolant temp. The gauge just shows you a green operating area and a red operating area and you are tickled pink with it in the green although the real temperature may be 235 or higher.

From the FSM: "Cooling fan speed is effected by many different conditions and can be adjusted from 10 percent to 90 percent duty cycle (PWM), 90 percent is considered high speed fan. When multiple cooling fan speed requests are received the ECM uses the highest cooling fan speed of all the requests. The ECM commands the cooling fan ON under the following conditions:

• Cooling fan duty cycle starts when engine coolant temperature reaches approximately 95°C (204°F) and reaches high speed at temperatures above 113°C (235°F).

• Cooling fan duty cycle starts when A/C pressure reaches approximately 1100 kPa (160 psi) and reaches high speed at A/C pressures above 2480 kPa (360 psi).

• At engine oil temperatures above approximately 150°C (302°F) the cooling fan duty cycle will be commanded to high speed.

• At transmission oil temperatures above approximately 132°C (270°F) the cooling fan duty cycle will be commanded to high speed.

• After the vehicle is shut OFF if the engine coolant temperature at key-off is greater than 113°C (235°F) or the A/C pressure is greater than 1720 kPa (249 psi) the cooling fan duty cycle is set to 50 percent, low speed. If the coolant temperature drops below 110°C (230°F) and the A/C pressure drops below 1660 kPa (241 psi) the fan will shut OFF. The fans will automatically shut OFF after 2 min. regardless of coolant temperature. "

Bill

 

Did you get your fan settings changed in your ECU? If not the fans will still come on at factory settings.