I had a brain fart and poured about 5 oz. of brake fluid into my radiator depository in my 2009 Jetta TDI with 41,000 mi. VW doesn’t recommend radiator service before 120,000 miles, but do ya’ll think I should flush it or even just drain and replace the fluid, or not worry about it?
Do a complete flush ASAP.
If it remains in there too long it could deteriorate the hoses and other rubber components including the water pump seal. DOT 3 is glycol based and traditional(green) antifreeze is ethylene glycol so there shouldn’t be a sudden disaster but the sooner the better I would imagine.
It sounds like you poured it into the reservoir, not the radiator itself. If that’s the case, and you haven’t run the engine yet, the brake fluid probably hasn’t gotten into the engine. In that case, you can just drain the reservoir itself and refill with the correct fluid. If you have run the engine, then you may have sucked some of the reservoir fluid into the radiator and engine, but probably not all of it. Worst case, a drain/fill at the shop costs you $100.
Definitely have the cooling system completely flushed and refilled as soon as possible before too much damage occurs.