[Scott65]

Sometimes I can get off track troubleshooting... So here's the scenario: Yesterday I was able to get the Pontiac out in what is for us exceptional performance weather. Cool, dry air, sunny and beautiful. Everything was fairly normal until I hit the highway. Normal warm up times, normal around town temps for this type weather. Hit the highway and look at the air/fuel gauge and its reading rich, which causes me to look at the laptop which also shows rich, but also I notice the temperature, 155 degrees... I have a 160 thermostat, which normally here in Texas means nothing. Usually highway temps in summer conditions are ~185°
Can't remember my car ever running under the thermostat temp in any weather. My thermostat "should" go closed under and until 160, right? This issue was causing the ecu to go back into warm up enrichment mode since I have it set to be done at 160. I can, and did, take it down to 150 for now, but this inconsistency I don't need. It got as cool as 153°. Am i correct in thinking my thermostat isn't doing its job correctly?
Edited to add: This isn't a gauge or sensor issue, as the two are in agreement.

[JLMounce]

The thermostat doesn’t act like an on off switch. It will actually start to open before the rated temperature so that it is typically fully open by that temperature or just past.

What is occurring is that even though you don’t have full coolant flow, the air temp delta is wide enough that it’s pulling your temps down.

My advise would actually be to go up to a 180 degree stat. That shouldn’t effect your summer cruising temps if they stay in the 185 degree territory, but it should be hot enough that your winter driving will produce temps above your warm-up enrichment threshold.

I deal with the same thing, except my car is almost impossible to get above 140 degrees this time of year with temps around 40 degrees.

[dataway]

Yep, I'd imagine you might actually pick up some power running it at 180 also. That's more in line with how the engine was designed to run.

With a 160 ... probably +/- 5% accuracy ... could maintain as low as 152 degrees and still technically be within tolerance.

Sounds like you have plenty of cooling capacity, a 180 would be perfect for you. Engine would be happier I think.

[Scott65]

I have a 180, or two... Guess that's the answer at least for the winter time. As long as it behaves as expected it can stay year round. Thanks for the input.

[lust4speed]

I've seen thermostats run under temperature with the extra 1/8" bleed hole is drilled. I would think that little hole wouldn't matter at all, but sure seems to.