MacBook Pro fan sound after motherboard replacement

What exactly spilled? All liquids are damaging but acidic drinks are worse than plain water. That includes all juices and carbonated drinks.

I don't like being the alarmist but this is an alarming situation that needs your immediate attention. This could get expensive. Get the computer evaluated immediately. There is nothing about spill damage that a user can fully mitigate.

Even with professional service, not all the liquid may be accessible and removable without replacing everything inside the case. Liquid damage is progressive. You can spend hundreds of dollars on service and still have a computer that fails weeks or months later.

Fans are thermostatically controlled by sensors on various sections of the logic board and on some components. When a sensor fails or is damaged, the fan/s go to maximum speed. A fan running at full gallop when it shouldn't indicates sensor damage and that could mean a new logic board.

Warranty does not cover liquid damage. AppleCare One may, with a big copay from you.

If you have homeowners'/renters' insurance coverage, those often cover damage to your tech. Put them on notice of a potential total loss immediately. At least theat wil limit yor oss to the cost of the deductible, usually $500 in the US.

MacBook Pro is not the same thing as a Mac Pro.

Click on this link to read about fans and fan noise in your Apple product. --> https://support.apple.com/HT202179

Who did this replacement? My inclination would be to take it back to the service place and ask them about this.

If a SafeBoot https://support.apple.com/en-us/HT201262 will not sort the anomaly—

Login and test. Reboot as normal and test. Caches get rebuilt automatically.

I would turn around a march it right back into the repair shop...

Apple-certified repairs — here you can Track the status of an existing repair

https://support.apple.com/repair

Check Device Coverage

https://checkcoverage.apple.com