I ran another test this morning, with the EVGA Precision X1 software. I set up an aggressive fan curve, then notched them all up a small amount:
With the GPU cool, it obeys this, and sits at 40% fan speed, and is silent. I then ran MSFS, and fired up EGLL, and moved the drone up to a point overlooking the airport with London visible.
As predicted, the GPU temperature started to increase, and the fan kept pace. However when it got to somewhere between 70C-80C, it stopped obeying the fan curve completely, and started doing that breathing thing again, ramping between 0-3500rpm. Looking at it now the fans are not even spinning, and the GPU just hit 90C.
I don’t think the issue is with the fans themselves. I’ll let it cool, and try setting an even more aggressive fan curve. If I can stop it from getting to that state where it starts ignoring it, it might be okay. When it got down to around 50C it started obeying the fan curve once more, and the fans came on, and stayed on.
But I think I have to face the fact I need a new GPU.
Got a 1080 Ti from eBay for £75. That will tide me over till I can get something better. I wonder if it managed to find any Bitcoins. 