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Is it harmful to drive 2 hours without thermostat?

I want to remove my thermostat just for ease of changing my coolant. I rinse my cooling system with distilled water 4 times. I fill up the whole system with distilled water and drive my car for 30 minutes and then drain the system and fill it up again. Without thermostat, this can be done easier.

I also use my blower to flush the old coolant with air and removing thermostat will help to drain more coolant.

Could driving for 2 hours without thermostat damage piston rings and cylinder walls? (Because of lower running temperature and colder engine) I can drive uphill to prevent cold operation of the engine.

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    A lot of faffing around for little, flush it properly and put it back together properly. Been done like that for years.
    – Solar Mike
    Commented Jun 21, 2021 at 20:33
  • If you drive uphill to keep the engine warm, what will happen when you drive back downhill?
    – DavidRecallsMonica
    Commented Jun 21, 2021 at 22:06
  • I meant I could drive uphill for 10 to 15 minutes after start-up to help getting engine to normal operating temperature faster in the absence of thermostat. I don't drive back downhill because the rest of the road is almost flat!
    – LFY MP7.3
    Commented Jun 21, 2021 at 22:25
  • And after your drive, will you drain the cooling system while on the flats, or will you return downhill to the beginning location where you do the mechanical work?
    – DavidRecallsMonica
    Commented Jun 22, 2021 at 1:32
  • I don't need to return to my previous place because I can park my car in the second location (my friend's parking lot) which is located a few miles further on the level ground after that uphill road. I go there and turn off the engine and let it cool down for 24 hours. I will never drain a hot engine to avoid thermal shock.
    – LFY MP7.3
    Commented Jun 22, 2021 at 7:23

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Assuming that you still have coolant in your system, you should be good for a reasonable time without the thermostat. Its main purpose is to keep the engine up-to-operating-temperature when it's COLD. Generally it's 100% open when it's hot out.

Probably the worst thing that could happen would be some slightly reduced fuel economy due to running the engine colder than it's designed to run.

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