Good morning.
It sounds like you may have a damaged head gasket from the overheating.
You may have repaired the reason for the overheating by replacing the thermostat but the failed head gasket is a result of the overheating.
You can get a chemical kit at a parts store and follow the instructions to verify or have a shop do a leak down test on each cylinder to find the exact area of the leak.
Roy
https://www.2carpros.com/articles/head-gasket-blown-test
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Tuesday, November 13th, 2018 AT 4:32 AM