Gotta problem. I have a 96 z28, Lt-1 5.7ltr with a/c , automatic,after market exhaust K&n cone airfilter, 160 degree thermostat and a power programer. The car only has 75,000 miles on it and until now has been very reliable. Recently it has been overheating only about 5 minutes after starting. the temp rises beyond 260 degrees just sitting in the drive way, driving doesn't help. The thermostat is good. I can't tell if the fan is coming on or not. It doesn't appear to be, not even when the a/c is on. The hose at the thermostat doesn't seem to fill and the heat blows out cool air all the time. The low coolant light comes on immediately, but the level is fine. It is running a little rough but no bad smell or smoke and it starts right up even after sitting. Dealership says there is coolant in the 7th cylinder,$1200 to take out the engine to find the problem. I think they are full of it. I'm no machanic, but it seems like something more simple. A fan relay maybe? As much as I would love to drop a new edelbrock in I can't even afford to get it towed right now. Any thoughts?

Change your oil and find if you have any coolant mixed in. Might have blown a head gasket. Coolant in the cylinder would prolly explain the rough running. As far as no coolant getting into the tube, the thermostat may be opening, but is your water pump actually pumping? That may be shot and prolly explains why nothings actually cooling for you...

Check your catalytic converter ...it may be blocked. It will glow red hot if it is.

Kev

Did you recently drain and refill your cooling system? The LT1 is widely known to hold a significant amount of air if it's filled improperly. This would be causing very little coolant flow creating all of your problems.

It sounds like it may be the ECM. The rough running, the overheating, the low coolant light coming on falsly, fan not coming on even with a/c. These are all things revolving around the ECM.

If he had it at the dealer and he paid a diagnostic fee, seems like he got taken in the shorts. If all the dealer found was the effect, they haven't found the cause.

The Low Level light is from the reservior, not from the engine. I would suggest to start from the beginning with a cold engine and remove the radiator cap for the fluid level. I'm sure there is a purge screw/tap on top of the engine in the coolant line to purge out most of the air. Total removal of the air will taken a few days to do providing the cooling system is tight and the reservior does not leak.

For the fan not coming on, could the ECM coolant sensor, the two-wire one, plus the other possibilites mentioned, leaving the ECM, actually PCM, last. If you select A/C or DEF, does the fan come on?

I agree with the trapped air comments. Also, don't rule out a bad cap. If the upper hose doesn't firm up when this happens, pressure is escaping and can let the coolant boil too soon. If fluid is lost then the trapped air issue can become worse.