Replaced a thermostat on a 2015 Civic and the temp gauge still acted funny

I put in a new housing and a fresh 195-degree unit, but the needle kept dropping at idle. Turns out, the old coolant was so degraded it wasn't transferring heat properly. Anyone else run into coolant causing a false thermostat diagnosis?

3 comments

3 Comments

henry3151mo ago

Yeah, the "old coolant" thing. Been there. Felt like a real genius after swapping a perfectly good thermostat.

betty_palmer1mo ago

My wallet felt that one too...

henry_martinez1mo agoMost Upvoted

That old coolant flush cost me $400 last spring. The mechanic said it was basically just expensive green water. Felt like paying for a fancy oil change with zero results.