400 sbc, aluminum radiator, LS fans, both on. Outside air temp 90 deg, A/C on, 75 mph, 2500 RPM does the engine temp of almost 220* seem appropriate.

 

That's hotter than what I like. But probably normal for these cars.
I'd prefer around 190 to 200 at 2500 RPM and highway speeds...

 

With similar temps (but likely much higher humidity) and a fully built 406 I run between 185-190 going down the interstate. This is straight off a datalog going off of coolant temp sensor. Keep in mind the gauges a lot of time aren't always accurate. Personally I would like to see temps below 200* at all times.

Is your lower air dam still in good shape/present?

 

Is the engine actually running 220F on a 90F day with the AC on at 75 MPH? Or is that just what the factory gauge is showing?

At 75 MPH I can't imagine why you would need any cooling fans at all. At 75 MPH you should be able to take the LS dual fan and shroud assembly and throw it away and run cooler because you got rid of an airflow restriction.

 

This is true. Looking at my tune, my ECM shuts down fan at 65 mph. Override kicks it back on at 190*F.

With a fully intact air dam setup these cars cool well at speed.

 

Curious what thermostat the OP is running. With a proper airflow management, cruising along at speed, it should be pretty close to the thermostat temp.

On my 383, 180F T-stat, stock style plastic-tank aluminum radiator, AC on in 95F weather, cruising along on the freeway (fan programmed off at 35 mph) I'm doing a steady 180-185F. Going up a decent incline, I'll get to 190F, but that's about the limit.

 

If you are using a stock coolant sensor the fans don`t come on until 210 degrees. Now the factory gauge is notoriously inaccurate. Get a mechanical gauge if you are really worried about it. I upgraded all my gauges to Stewart Warner electric gages with the proper sender`s. Or get a Infrared temp. tool and point it at the water pump when reading hot. That is way more accurate then the factory gauge. Harbor Freight has them fairly cheep.

 

My air dam is in good condition and in place as it should be. My 180* thermostat normally runs (except on warmer days 85*+) at the mark between 100 & 220 as in pic. I have switches on both fans with indicator lights on each as to not alter the OE setup. The block was hot dipped/cleaned when I did the build last fall. Aluminum radiator is somewhat new and was flushed both directions at build time. A/c condenser is new last year. All the fins on the rad. & condenser are in good condition, no blockages & none folded over or crunched. I think it's runs a little warm all things considered. At 60 mph it's a little cooler but still above the 180. Maybe thermostat isn't opening all the way???

 

General rule of thumb. If it runs cooler in town then it does on the highway you have an airflow restriction at speed or a issue with the under car pieces (air dams). These cars cut the fans above a certain MPH from factory because they are perfectly capable of cooling themselves at speed without them.

If you run cooler on the highway than you do in town, you have a lack of airflow coming from the fans.

 

Should my air dam tilt forward more at the bottom?

 

'Looks fine to me...