I just fixed my engine temp sensor wires on my 2005 Civic VTEC. If it matters it has a Mishimoto full aluminium racing radiator filled with 100% distilled water and a 170 degree Stant thermostat. On My Scangauge 2, the engine temp stays between 182 and 188 on the highway and between 195 and 205 in traffic. Shouldn't the temp on the highway be the temp of the thermostat? I understand why it runs warmer in traffic, but shouldn't it be running closer to the temp of the thermostat on the highway? Thanks in advance.

 

Normal operating temp is between 180 and 200 degrees, this is pretty much for any aluminum engine Honda (at least anything from the 80s and newer). There will always be fluxuation as the thermostat opens and closes, it doesnt react as fast as the waterpump can spin. You meant you are using 100% distilled water as a 50/50 mix between that and regular coolant (ethylene glycol), right? In short, your temperature readings accounting for fluxuation and all are okay, you don't need to worry.

 

I am working on flushing the oil out of the cooling system from when my last motor blew up.. That is why I am not using antifreeze. Thanks for the help.

 

They sell radiator flushes to help flush out oil. It's very important to use 50/50 since coolant itself helps prevent your system from freezing in freezing temps and from running too hot when it's hot out.