Good God stick to the oem t-stats. Lots of problem reports on the Accord forums when using aftermarket t-stats. The Civic probably wouldn't be much different in that regard.
edit: found this:
Originally Posted By: ;774689
Aftermarket stats cause issues in Hondas and many other imports.
The guy on the Ody forum is incorrect. The stat is NOT fully open at 172 and his C to F conversion is a bit faulty. If his stat was fully open at 172 its no good.
The factory stat that Honda uses starts to open at 176 and is completely open at 194. Your factory stat could be opening early. You'll never see this on the gauge, as a "normal" reading is 140~220. If you have a scan tool, watching the ect is a good way to know if you have any bleed thru the stat, it should come rather quickly to temp, maybe 5 minutes max even in subzero weather when moving.
Aftermarket stats tend to stay completely closed, then snap open rather suddenly at 195 or higher, causing thermal shock to engine components, especially in very cold climates.
I've seen issues with aftermarket stats that open very late, brand new, a 195 stat may not even begin to crack open until 210 or 215. This isn't good. Then a sudden rapid infusion of cold water when it pops open occurs.
My '04s heater works fine, at temps in the low teens it's able to get quickly to and maintain a set temp. If you pick full hot, it'll always blow full temp and not regulate, unbearable to me. When the system regulates temp, which will blend in outside air, as needed, through the face vents if the temp gets to or above the set temp. That can be a bit shocking, I'll admit.
I've measured 170 coming out of the vents at max heat.