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Discussion Starter #1
I think I have an open thermostat in my car. The heat doesn’t really get hot. Also the car smells rich. It hasn’t always smelled that way. On my other cars is it’s stuck open they run rich and the MPG’s go down but they are newer OBD2 cars.
 

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Its too easy to just pull it and check it. or just go ahead and replace it.

You can take a temp gun and put the thermostat in a pot of water set it to boil when it opens see how hot the water is if it a 180 it will open at 180 and so on.
 

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My tempo recently had this. Will warm up fine sitting still. Once you drive temp will go to cold on gauge. It will plummet pretty quick , heat will still work.
if you purchase new thermostat please boil it in water to make sure it opens correctly.
 

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Its best to run a tstat with the factory rating.A few reasons why.
A stuck open thermostat or one with a lower than factory rating can cause more harm than good. Remember 200 degree water is bad for us,but its not bad for our 5.0’s! It’s been proven that running too cold is actually a detriment to the engine.Your focus should be cooler intake air,not a cooler engine block.Engines do better at producing less emissions and running more efficiently when running at a certain temperature.So the programming on the eec was all done under the assumption that the 5.0 will be running hotter than us enthusiasts feel comfortable with.So if your engine is built & programmed for tolerances running at 200+ degrees,changing the values can have adverse effects.When you first start the engine, the ecu is operating in open loop mode to help the engine & converters warm up to operating temp.During this mode, the ecu runs the engine on pre-set fuel & timing values from a lookup table,but the ect & act sensor output is also used.When the ecu is happy with what’s going on with the engine,it transitions to closed loop.In closed loop,the ecu does everything it can to reach the holy grail/stoichiometric air/fuel ratio (14.7:1) for better MPG/efficiency and it does this by adjusting injector pulse width using the info sent from the O2 sensors. Closed loop mode won’t happen if the ecu thinks something isn’t working correctly.It’s worth noting that it’s a time-delay,not a temperature check for closed loop operation and it could actually go into closed loop even if temps are lower than oem specs. Also the ecu increases pulse width by 2% for every 10F below 190 and this mode is activated at just under 180 degrees.
If you daily drive your fox alot,a 192-195 thermostat would be your best bet as you’d get the most efficiency. A lower thermostat temperature can also make it harder for you to pass a emissions test. When the engine reaches a operating temp of 190+,the ecu will also pull 2 degrees of timing.
Make sure your radiator cap is good too.
 

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Discussion Starter #6
Thanks for the info. I run a stock 192 degree t stat. I figured the heat issue out so I’m going to do a tune up and go from there.
 
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