That's good to know. So it was hot with c-lightning or lnd?
I was running LND on the Pi. I don't think it matters; It would have been hot with c-lightning as well. I don't remember how much CPU LND was using on average. I believe that bitcoind was stressing it the most.
I also tried running ElectrumX on the Pi but I couldn't stand the noise of the fan which started kicking in even more frequently. The initial sync was taking so long that I eventually gave up.
Oh damn. Yeah I'm not kidding when I say with a Pi (model 3 though) it took me weeks for the IBD! 
With all these issues, I'm wondering why even so many people bother with SBCs then. I mean for nodes. They're great to put on / in a robot or other embedded environment, but a new Pi Model 4 with 8GB RAM and 1TB SSD + case and PSU runs about 200 bucks from the top of my head.
You should easily be able to get a used laptop or Intel NUC with 8GB RAM, 1TB SSD and much more power (and thus quieter at the same load) for ~200.