170 Degree Thermostat Pros/Cons

[JMR76]

I had the same experience, especially in cold weather.  I had the tuner adjust the fans to turn on a little later, still with the 170 TS and my engine temps run a little cooler. 

Sounds opposite, I know.  I noticed in cold air, the fans had been running and the TS housing remained ice cold until the engine temps got to around 186, then I could feel the TS open and the engine would cool down.

In warm and hot weather I didn't have this, the TS seems to be open more, so the temps would stay lower and fans ran fine.

[JMR76]

I should add that prior to the TS opening, the Fans were still blowing ice cold air keeping the outflow tube to the TS ice cold, but the inflow to the radiator was hot.  Again, in warm weather this didn't apply.

[Tuner Boost]

One of the keys to tuning any engine, and especially boosted engines, is preventing knock or pre-ignition.  Heat alone can set off the combustion of the air fuel mixture (think diesel engines and glow plugs) before the spark plug goes off.  At the wrong location and time of the piston stroke the effects can range from the car pulling timing lowering performance to catastrophic engine failure.  If you compare a naturally aspirated engine and their boosted twin you will generally find a lower compression ratio on the boosted engine.  The more air is compressed the hotter it gets so the goal here is also preventing knock.  A lower thermostat can usually keep the overall operating temperature of the engine down.  This is also partly why lower intake air temperatures are a goal (the other being cooler air is denser, more air=more fuel=vroom).

The problem with all of that is emissions.  I believe the engine burns the fuel more completely at higher operating temperatures lowering emissions.  Since the engine is designed to run at these temperatures to meet emissions standards all of the sizing of the parts fitting together are designed around that temperature range.  Too cold and everything contracts causing slop between all the parts.  Too hot and the parts expand and won't fit together.  Expanded parts cause increased friction causing more heat causing increased expansion causing increased... until the engine seizes.  This is why you shouldn't put an engine under high stress until it has warmed up to operating temperatures.

So...
Normal Tstat
     parts fit together
     less emissions
     better heat in the winter

Lower Tstat
     part slop (can increase wear, oil blow-by piston rings? )
     greater emissions (but people delete cats from downpipes so...)
     lower heat in the winter
     ability to run more advanced timing
     denser air charge due to lower underhood temps

Now in reality I'm not sure the difference in temps between the two tstats will cause enough variance in part sizes to cause any problems.  People have definitely noticed lower air temps coming out of the vents when using the heater. 

You really should have a tune to run a lower tstat.  The ecm will throw a code if the engine doesn't reach the programed operating temperature in a set time frame.

Excellent post with great understanding. The only other thing I could add is anything below 200*F and there is less flash-off of unburnt fuel and water in the crankcase, but that can be dealt with using the RX PCV system as the ecoboost has such an inefficient system stock.  The denser the air, the more room for oxygen molecules, the more power can be made.

[Bigjht]

Thanks for everyone's insight on this.

[jm@ReischePerf]

You guys brought up so many things, it's hard to address them all but dalum's post is pretty spot on.  The power is in the tune, the lower temperatures just make it safer.  More pros/cons info here: http://www.reischeperformance.com/WhyLowTemp.html

A few more thoughts:

You guys have cold-side thermostat setups which means the thermostat housings don't get hot, when the thermostat opens, it lets in chilled coolant from the radiator... opposite of a traditional setup.

Yes, the heater will be a bit cooler but I'd be surprised if most people would be able to tell the difference.... Personally I can't between a 180* or a 170*, the heat is still very hot.

More engine wear?  Not in the oil analysis that I've seen but there is a sound theory behind this, I've just never seen any evidence of it with our thermostats.  At any rate detonation is far more dangerous for your engine.

Low coolant temp engine code?  Not typically with our 170* thermostats, tuned or not.  I'm not saying it's not possible but I've never had a customer come to me with that issue.  I did see a post somewhere saying somebody knew somebody that had a problem but I can't be certain what product the 3rd party was running, he did not contact me.

Higher emissions?  Possibly, but plenty of vehicles have passed California emission tests with our thermostats (however not technically legal for street use in CA) which are some of the highest standards around.

If your fan is running all the time or excessively then the fan settings are too low and this should be addressed by retuning.