Hey guys and gals! Currently in a bit of a spot with my vehicle and was looking for some insight before taking her into the shop. I’m driving a 2002 Volvo S80 has about 102000 miles on it. Yesterday I was driving home from Hartford CT to MA when I was pulling into my driveway and got a ‘low coolant’ notice. I allowed the engine to cool off, popped the hood and removed the cap to my coolant reservoir. Upon opening, I discovered a sludgy substance inside the cap and reservoir. I topped off the coolant and the sludge dissolved. As I pulled in from work this morning the same message popped up then disappeared. So my question to y’all, is, what would be causing this and how much should I expect to pay. As well as how will I know if I’m being screwed out of money over the matter. Thanks for your time!