trying to find and replace thermostat on my 2.0L turbo, when I drive it with scan on the temp goes up and down.

 

Is the vehicle overheating? Does your engine temperature gauge fluctuate or are you referring to scan tool data?

If scan tool data, that is normal for a properly functioning vehicle to have fluctuations in ECT (engine coolant temperature) sensor data. The ECM (engine control module) smooths this information out when displaying it on the gauge in the cluster, but a properly functioning thermostat will modulate flow based on the temperature and in doing so, the temperature will fluctuate.

 

The car is at 166 degrees driving around town, 180 degrees at cruise, have to pull hills to get up to 194 degrees. All at 25 degrees outside, Northern Montana

 

Are you referencing gauge readings or scan tool data? The gauge isn't meant for diagnosis, only a visual indicator to the operator; off to either extreme is bad, but anywhere close to the middle of the gauge sweep is fine.

With colder outside temperatures, it may be difficult to get a good heat soak on the engine without a grill cover. I don't know if those vehicles have the active grill shudders that were on some of the previous small cars (and were quite problematic).

With that said, in looking for a thermostat for your vehicle, all I am coming up with is an Engine Coolant Flow Control Valve assembly on the TascaParts Website for a 2021 Blazer LT 2.0L Gas - Cooling System - Water Pump Section. That will set you back over $200 though...

Based on that information, I incorrectly assumed that GM would not have gone away from the typical thermostat design... Wow, way to over complicate a device that has been practically unchanged for well over 50 years... I'm not sure what the operation of this flow control device is like in terms of the temperatures that can be expected. Would need to see if anyone has access to the factory service manual theory of operation on this device to see what the expected temps actually are from thier perspective.

In the grand scheme of things, I wouldn't be too terribly worried about it if there are no stored codes for not coming up to temp in the desired time, etc.

 

To answer your last question, those readings I had where on a scan tool, also my wife said the heater it didn't seem to warm up when it's cold out. thank you

 

I am not saying that something isn't wrong with your car, but 160F should be enough to get decent heat inside. How quickly does it come up to that temperature? If not quick enough, it should throw a code.

If you choose to replace the coolant flow control valve, the part number is in one of the links I provided above. I do not have access to the factory info for your vehicle to be able to tell you whether or not there is any calibration procedure required.

 

Ok thank you for the help