Coolant thermostat malfunction on new engine swap

[BigGuylilcar11]

I recently had an engine swap done on my 2015 mirsubishi mirage DE automatic. I got it back about 2 weeks ago, but the check engine soon light keeps coming on due to the coolant thermostat staying open. They have replaced it about 4 times with new thermostats and it keeps failing. They finally said they will get one from mitsubishi themselves to see if this will fix the problem. Has anyone had this problem, as in do off brand parts malfunction and are original dealer parts needed? Any information will help. I'm tired of taking the car in just for them to do the same thing and keep having the same problem.

[Eggman]

I recently had an engine swap done on my 2015 mirsubishi mirage DE automatic. I got it back about 2 weeks ago, but the check engine soon light keeps coming on due to the coolant thermostat staying open. They have replaced it about 4 times with new thermostats and it keeps failing. They finally said they will get one from mitsubishi themselves to see if this will fix the problem. Has anyone had this problem, as in do off brand parts malfunction and are original dealer parts needed? Any information will help. I'm tired of taking the car in just for them to do the same thing and keep having the same problem.

The problem might be with aftermarket thermostats. Refer to the following two threads for more info:

Engine never warms up need help!
Green temp light stays on (after flush & thermostat replacement) Solved!

[Fummins]

The part could be faulty or the mekanik isn’t installing it correctly. The rubber gasket has a spot where the thermostat sits inside it. Usually when the thermostat is removed the gasket doesn’t come out with it.