If you figure it out, let me know. Been suffering this for a long while just about.I’d guess it’s just the thermostat. First time I changed mine it ran warm for a while and worried me eventually settling back to normal. Now my water pump went out so I replaced the thermostat again and it fluctuates 188-204 constantly.
200* t-state gets to 205*, then drops rapidly to 193* and then rinse and repeat. Had a whole huge thread about that lol.
On a 190* tstat I sat 185* without budging usually which is why I tried the 200*. I enjoy the 200* in the winter so it's stayed. I've tried a few different tstats from a few different brands to no change. Only change was the 190 to the 200.