Faulty Temperature Gauge?
 

My 1990 L98 seems to run hot in warm weather (like so many others) according to the gauge. When its cool outside the gauge shows no more than 140 tops on the road as well as in traffic. Once the weather heats up so does it. Usually around 170 in the road and as much as 240-250 in traffic. To say the least I was a bit bothered by those temps.
Today I took it out and let it climb to operating temps of around 180 on the road (outside temp was 80) and brought it back home and let it idle in the driveway until the needle on the gauge showed 240-250. I used an infrared temperature gun and measured the temps on the upper and lower radiator hoses. This is what I got:
Lower hose - 195
Upper hose - 175

Are the hoses the most accurate places to measure the temps? If so is it safe to say the gauge just isn't accurate.

Hoses are rubber. You are taking a reading of the outside of an insulated hose which will get you a very inaccurate reading. Why not shoot the radiator?

Good point, hadn't thought of that. The problem with shooting the radiator is a line of sight to it. There is one small opening on the passenger side of the housing that I can shoot through but then I am taking the reading at an angle (not sure if that matters). Even then I am getting a reading of no more than 200. I haven't had the car on a lift yet, can you better see the radiator from the underside?

I can see mine from any side. :D
https://cimg7.ibsrv.net/gimg/www.cor...5104312743.jpg

If you're doing it through a 1 1/4 (+/-) hole top of radiator support it would be safe to assume I believe that you've got the right side tank.

If this is a C68 ATC A/C you can check the TEMP using the C68 control panel, That's likely more accurate as that's what the ECM sees using the CTS/ECT.

Can you hit the thermostat housing with an infrared thermometer Probably as close to the actual CTS a few inches away as possible?

Very possible, I will have to take a look.