Factory gauges are notorisly inaccurate & I'd bet your thermal gauge is telling you the truth. Not sure what the factory thermostat setting is for your particular engine, but it went up to the 205-215 range on everything years ago. Reason being a hotter engine passes emissions tests easier & also, since the system is pressurized, the coolant's boiling point is raised substantially.
If you want to lower the coolant temp, you can get a thermostat set for 180* & I've even used one set @ 160*, but the factory thermostat was most likely a 205 or 210. And the temp should stay the same all the time, winter or summer, idle, city driving or going down the highway - that's what the thermostat is for - to allow the engine to warm up quickly then stay @ the same temp all the time.
Friday, September 18th, 2009 AT 2:04 PM