Hi all! I checked the coolant on my 2018 Honda Accord Sport (1.5t, ~61k) and noticed this weird substance. At first I thought it was dirt, but it wouldn’t make sense for dirt to get there. I googled it but there were many things it could be so I’m still unsure.

I use premium fuel, oil changes every 5k, fuel injector cleaner every 5k, and don’t abuse the car. It sometimes shakes on cold and warm starts, but goes away after 5-10 seconds. No CEL.

Any idea what it might be? The coolant is still a blue color.