PCIe Slot 1 Temperature - Mid 2010

What card are you using? 5870 I assume?

In addition, how long has it been since you have *thoroughly* checked inside your 2010 for dust? You will find that the front fans, the CPU heatsink(s) and the GPU are the main places where dust will accumulate.

Pull the GPU and HDDs and vacuum the chassis but get hold of an air can to deal with the CPU and memory board as well as the GPU. A good blast of compressed air will make sure that air can flow through the PCIe bay. If the PCIe fan and also the GPU are dust-free, then air should be able to flow well.

If you are out of AppleCare (or are just confident in your skills) I heartily recommend replacing the stock cooler on the GPU with something more effective and quieter.

I placed an Arctic Cooler Accelero XTREME Plus with fitting kit VR001 on my (almost new) 5870 and have been running it quiet and cool for over a year and a half now. I discussed it in THIS THREAD.

The reason I picked that cooler was because it was one of the few at the time that gave fair cooling to the VRM chips on the 5870. It is a tight squeeze and is 2.5 slots high but if you have a single GPU it may be worth considering.

EDIT : for your info here are my recorded temps...

AMBIENT : 23C / 73F

STOCK COOLER : Idle 38C / 100F, load 63C / 145F

Accelero XTREME Plus : Idle 27C / 80F, load 52C / 126F

I have Hardware Monitor, and I don't see a temp sensor for PCI slots. I thought Temperature Monitor was the free version of Hardware Monitor, so wouldn't it have all the sensors included?

MPs don't have a PCIe slot temp, so maybe it's reading something else incorrectly?

Take a screenshot of all your sensors and I will (or somebody) will compare them.

The expansion bay fan does seem to think there is something hot in there and a 5770 would not generate much heat at idle.

I would recommend you fully remove everything and give it all a good clean and also make sure the 5770 on-board fan is spinning well. It should be drawing air from the PCIe bay, passing it over the GPU and exhausting directly out of the back. If there is fluff and dust in there, that airflow would be impeded and if the fan was spinning poorly, again the temps would rise.

At least you have plenty of options for replacing the 5770 cooler if it is defective.

Looking at the Expansion fan speeds, my fan with a 5870 runs at minimum speed at idle.

Do you have an Apple RAID card in there at all? I do know that raises the PCIe bay heat a lot.

Strange.
My istat Menus pulldown as in your screenshot shows four memory slot temps instead of three, then northbridge, then the two power supplies... no PCI slot temp.
I'm on a 2009 with 2010 firmware, so maybe there is actually a different sensor setup on the 2010 hardware that I don't know about.

Running some video stuff on a second monitor. I see anywhere between 150 and 180 with my 5770. Expansion slot doesn't spin up. Normal operating temp.