Last year my Z28 started running warmer than normal. Onced it warmed up, it used to operate at about 170-175, except on really warm days. Now it will get up to 185-195. My fans are programmed to come on at 180, so this means they are on all the time once the car warms up. Once they do, my alternator has a difficult time keeping up with those, my MSD, window switch, bottle warmer and all the normal systems of the car. I do have a 160 degree thermostat, but it is a few years old. The car has never overheated. Is my thermostat bad?

 

Have you checked the fluid level? You can also test the thermostat in a pan of water.

 

Yeah, fluid level is full.

 

They are around $5 so I just replace it when I suspect it might be bad. Probably something not working in the cooling system correctly. Maybe the coolant mixture is off or the water pumps not doing its job.

 

Being warmer by 10 degrees doesn't indicate a bad thermostat...they tend to fail closed so the temperature goes straight up off the gauge. Thermostats for an LT1 aren't 5 bucks....more like $18 so better to test it first.

So, if the thermostat tests out fine and the system is full of coolant, the next things I would check for is a clogged radiator followed by low coolant flow. With the car up on ramps, and the fans unplugged, reach between the fan blades and feel the radiator surface. It should be uniformly warm from top to bottom and side and prgressively cooler from one side to the other. If the radiator is, for example, hot at the top and cool at the bottom, the radiator could be clogged. If it doesn't seem to be cooler from one side to the other then I'd suspect the waterpump isn't flowing what it used to and low flow is causing the temperature increase.

Good luck!

 

Also don't forget to check the airdam, it's a critical part of the 4th Gens. cooling system.

 

The water pump is brand new, and this problem has been the same between the old and new one. Air dam is fine too.

 

Replaced the thermostat yesterday. I figured if I was going to go through the trouble of taking it out, it was getting replaced since it's 8 or 9 years old. Problem solved. Stays at 170- 175 again.

 

it probably stuck partially open. happened to my GMC Sierra (Vortec 350). so i know from experience it is possible

 

Yeah, I knew it was possible too.