I had a bit of time to spend on the car earlier, so started off by eyeballing the water levels... and it hasn't changed since I topped it up, despite a fair number of miles driven. What I thought was a wet patch below the thermostat is just a bit of oil. No mayo in oil, no oil in water... Guess I'll just try to keep an eye on it for now!
Which leads me onto the broken temp gauge - it only ever reads midway, and I wanted to make sure I don't accidentally overheat the car, so fixing it was a priority. I removed the cluster and inspected for dry solder joints, but it was all good on that front. As an experiment I tried the gauge cluster out of my other 940 and that worked fine!
Now I didn't want to swap the clusters over - the other Volvo is about 70k higher mileage - so I swapped the temperature gauges only, and that seems to have done the job. Inspecting the old gauge there's no obvious damage and it moves freely, so not sure what'd wrong with it.
After that I had enough time to do a couple of minor jobs - a new reverse switch brought the reversing lights back to life, I disconnected the seatbelt warning lead so I don't get a horrendous ticking every time I turn the ignition on, and I replaced a non functioning horn with another off the other 940. They are equally crusty, however, so new ones will be ordered.
Finally I spotted something a bit odd - it looks a lot like a horn - below and to the left of the expansion bottle in the picture. Is it part of the (currently non-functional) alarm system?!?
