I put windshield washer fluid into the coolant by mistake - what do I do?

How much? This vehicle is one of the few that use a pressurized reservoir as part of the cooling system. That reservoir only holds roughly a quart of fluid when it's cold, but there's plenty of room to overfill it beyond the "Full" mark. Since the engine hasn't been warmed up yet, there's little chance much washer fluid mixed in with the coolant in the engine. I'd use a turkey baster to suck out as much fluid as possible from the reservoir, then add a 50 / 50 mix of water and antifreeze to bring it back to the "Full - Cold" level. If you can see the fluid level through the side, the reservoir is typically at the "Full" level when it's half full and the engine is still cold.

If the reservoir gets overfilled, coolant will simply bubble over and make a mess on the ground the next few times the engine warms up. Each time the engine is stopped and cools down, the coolant will contract, and air will be drawn back into the reservoir. Assuming there's no other problems, once enough coolant has been spit out of the reservoir, the level will again stay between the "Cold" and "Hot" levels.

Washer fluid is designed to evaporate, so any that does make it into the engine's cooling system will be the first to turn to vapor, get pushed into the reservoir each time the engine warms up, then will get pushed out the reservoir cap as the coolant expands. When the engine cools down, fresh air will be drawn back into the reservoir, like normal. Over time, all the washer fluid will evaporate away.

This has nothing to do with the water pump or the engine running. It is strictly an issue of changing temperature. As coolant heats up, it expands quite a bit. That's why there's the need of the reservoir and why we always start out with it less than full.

The typical story would be there's a quart of air at the top of the reservoir. When the engine is started, as it warms up, the coolant expands and we'll say half a quart gets pushed into the reservoir. It's not uncommon for a few tiny bubbles of combustion gases to find its way into the coolant too. Those also work their way into the reservoir. With this expanded coolant, there's still some air in the reservoir. On this model, the cap keeps the coolant under roughly 15 pounds of pressure. That greatly increases the boiling point of the water in the coolant. If the pressure increases even more, some of the air gets pushed out by the relief valve built into the reservoir's cap. That's where the washer fluid will get pushed out as a vapor, a little each time the engine goes through that warm-up cycle.

When the engine is stopped, the coolant cools down and contracts. Liquid is drawn back in from the reservoir. That's why you'll see the level in the reservoir go down over about an hour. Most engines today have at least some parts made from aluminum. Those transfer heat very quickly to outside air, so it's not uncommon for hot engines to cool down within minutes of being turned off.

Depending on how much washer fluid was added, you still might consider sucking the reservoir empty as possible with a turkey baster, then adding some fresh coolant. Alternately, if the vehicle's regular maintenance schedule suggests it's time to replace the coolant, this would be a good time to do so. We can do a complete flush, or more commonly, a drain and fill. Drain and fills don't get all the old coolant out, particularly that which is sitting in the heater core in the dash. The reason drain and fills are normally sufficient is not that the antifreeze wears out. It's because the additives in it wear out in roughly two years. Some vehicles today come with longer-lasting coolant, even up to ten years, but I don't really trust that. Antifreeze is alcohol and will always be alcohol. It's the seal conditioners, anti-foaming agents, detergents, and most importantly, corrosion inhibitors, that wear out. That's why we want to replace the coolant periodically. It's to replenish those additives. Even if some washer fluid has made its way into the engine, it's going to work its way out over time, and with a drain and fill, any left in there will be insignificant.

I'm glad you are concerned enough to ask about this. I wouldn't get too excited, but it does give me another opportunity to point out a much more serious wrong-fluid problem. That has to do with any type of petroleum product mixed in with brake fluid. That includes engine oil, transmission fluid, gear lube, power steering fluid, penetrating oil, axle grease, and on rare occasions, even fingerprint grease. One drop of any of those products has the potential to turn into such an expensive repair as to make a ten-year-old vehicle not worth repair. Problems in other systems can be caused by wrong fluids, but none as serious as with brake fluid. The worst fluids for cooling systems are oil-related because over time, oil rots radiator and heater hoses from the inside. If you have to put a wrong fluid in the cooling system, washer fluid is probably the least harmful.