Most unusual temps for a C5. My '04 C5 always cruised at 195-200 w/ or w/o the A/C...didn't seem to make any difference. Temps soared to 225+ in heavy traffic. When I got the C6 last Sept it behaved much the same till I installed the 160 deg thermostat. While the higher temps may not affect operating efficiency, it just makes me feel better knowing that there are cooler temps under the hood:yesnod:

My numbers are for A/C off.
Your '86 is a different situation, since the thermostat is located in the convential position- not in the engine water inlet side as in the C-5 and C-6.
Yes, your '03 will run at 172 but ONLY WITH A 160 STAT. A 180 stat will not run at 172 in a C-5.
Let's remember the original issue was a 180 stat in a C-6.
As I said, a 180 stat in a C-6 will not give you 180 running temperature. A 160 stat will give approx 180 running temp at normal cruise, A/C off.
A Vinci 170 stat will give you approx 190.

Mt experience agrees with yours. I ran about 196 at cruise with the OEM stat in my '07. As you say, your '04 was about the same- it had the C-6 style stat.

I guess thermostats must have changed substantially from my younger years. Back then, the only thing the temperature rating meant on a thermostat was the temperature at which the thermostat would OPEN. Everything else was exactly the same on those thermostats. They didn't allow MORE coolant to pass while opened, and didn't change the running temperatures at all. A 180 degree thermostat would open at 180 degrees. A 160 degree thermostat would open at 160 degrees. Once the coolant reached full operating temperature, it didn't matter what sort of thermostat is in place. :shrug01: :shrug01:

So then the general concern is too much heat under the hood and because Florida is hot and humid anyway, a 160 thermostat will prolong engine life and parts. Is this the general consensus or is there more to it?:shrug01:

There is more to it.
High coolant temp is one of the parameters that causes the ECM to retard timing, thus affecting performance

:yesnod: Agreed...Maybe its my imagination, but I can tell a performance difference @180 vs 210-215.

Not your imagination, the pcm pulls 3 degrees of timing when the ect hits 212 degrees and 6 degrees at 230 on C6s.
One of many things that can be programmed out.

http://www.z06vette.com/gallery/data...ection-med.jpg

So performance is improved with a lower thermstat. Will this only work if the fans are readjusted? Are there specific name brand thermostats that work best or doed it even matter? Mark

Performance is maintained if the coolant temperature (and inlet air temperature) stays low enough such that the ECU doesn't pull timing. A lower thermostat helps and may be enough if you don't sit idling for long periods. If you do, such as in the staging lanes at the drags, reprogramming the fan temps will help.
All the C-6 160 aftermarket stats I've seen are manufactured by AutoRad, and sold be several vendors. Quality control is lousy. I had a so-called 160 that ran at 189. My current 160 runs at 181 at cruise. Same brand.