Don't be so quick to draw that conclusion. Yes, you guys have had decent cruise ECTs using thermostats that leave the bypass open for a couple reasons:
1. The fan is being run a lot or constantly to achieve that ECT.
2. The thermostat housing favors high flow to the radiator and hinders bypass flow once the t-stat opens. This helps maintain decent temps while cruising but when you really bring the heat on you need to be able to completely shut down the bypass to maximize cooling capacity.
Someone recently reported to me that an improper low-temp thermostat works ok on the street but actually performs worse on the track than the OEM t-stat which is exactly what I would expect from an open bypass.
I promise you that this new 170 t-stat will outperform any 160 SOHC stat with better cold weather ECTs/warm-up but most importantly when under a lot of WOT.
