New temps with grey thermostat.
 

If with the stock thermostat I'm running at 188 on the freeway and 199 in town, when I replace the thermostat with the OEM gray low-temp one, am I expecting to see highway temps at 180 and in-town at 190? Is it really that much of a difference? I finally got the damn system nicely bled after all that cooling system work, and the last thing I want to do right now is bust it all open to swap out the thermostat to the gray one. Going into summer, it would be nice if the temp savings really are substantial, but if not, I'd rather leave it nice and closed up for now. Dad needs a break.

It just gives you more headroom with a 180 I run 183 - 188 on the low and around 194-196 at speed. If my high gets above 210 during a hot dya driving that indicates a problem. When you shutdown, your temps will still climb so that extra 10 degrees can be critical to preventing damage

I'm 188 at highway speeds and under way around town, Usually no more than 197 at stop lights etc. As mentioned above, you wont get much lower than 188 but the high end will be lower, given a proper bleed of course. You won't see highway temps at 180 unless you do the inline mod... The absolute lowest I've seen is 183.5 on a long downhilll stretch of freeway.

210F = I watch like a hawk & if it goes down all is well. If it hits 215F and shows no signs of dropping = something is up.

Temps will go up/down, the key is making sure it drops. If it just keeps climbing = check it out ASAP.

I see 84C=183F (downhill cruising) to 95C=203F (max point longer idling, before it goes down again by increased fan rotation and thermostat flow). This is after replacing the thermostat (180 instead of stock), fan and doing a cooling system flush. The thermostat contributed to about 70% of the temperature reduction, I did it step by step in the order mentioned to see the effect. Before I got to 104C=220F (longer idling) and the electric fan went on all the time. Now there is no more electric fan operation. I still need to put in a new radiator and this will probably reduce temps by another few degrees.

Location has a lot to do with temps also. As soon as it heated up in SETX I went from 184-193F to 193F-206F. Gotta love the change in seasons! The #1 thing I always monitor is when the temps start to climb. As long as they drop = all good. Changing speeds, moving in/out of traffic, load, and weather can drastically change how the engine cools.

Out on the trail last year I saw temps of 209F, slapped it into a lower gear, and the clutch fan engaged and I went down to 188F. Had it not gone down I’d have found a spot and let it cool down.

Just open the windows and turn on the heat.

Its flow...the stat can only open so far.

Good temp solution but easier to say and do when you don't live in the depths of hell like some of us feel like we live in.

I thought that the heater core on D2s circulated coolant whether heat is selected or not. Which, if true, means this wouldn’t help unfortunately :/

It circulates all the time, but if you turn on the blower it will act like a mini radiator being cooled by air. However I’ve personally seen it work for a few minutes, then the temps can rise again.