Explain Coolant Reservoir?
 

I thought I understood the coolant reservoir but maybe I'm missing something.

My Civic got pretty hot a couple times recently. It vented coolant into the reservoir but it seems to stay there unless I pour it back into the radiator myself. Isn't it supposed to get sucked back in automatically??

Does it mater whether I vent it later after it cools a bit by loosening the radiator cap?

If you're wondering why it got hot (227 deg F this morning!!), it was due to too much grill block and me not paying attention to the ECT display in ScanGauge. Yakking with carpool buddy. My bad.

If your radiator cap has a crack in the seal then it will not pull fluid back, that is why it's recommended that you replace your radiator cap every few years.

Agree, highly reccomend a new pressure cap. My car would always get hot, not overheat but it would regularly run at 215+. Normal temp is around 200. New pressure cap and problem solved. It got so bad before I changed the t-stat, both were bad, I was reading over 240 on a 60 degree day.

Someone explaining it almost too well:
http://www.youtube.com/watch?v=0JdDWWoX-70

(And if you loosen the cap while the engine is cooling, you ruin the suck)

Does the recommendation to replace radiator cap every few years apply to vehicles without traditional radiator caps as well, where the only pressure cap is the one on the overflow resevoir?

Sounds like cheap insurance... thanks.

Thanks guys! Will get a new cap ASAP.

Price out OE before you buy anything else. The cap should have a check valve that allows the coolant to go back to the radiator when the engine cools down. Some systems also need to be bled to get all the air out. There is a fitting (maybe 10 MM) that you loosen while the engine is warm and running. It will bubble out air until it gets the air out, then you will see coolant coming out without air bubbles. After that check you reservoir when the engine is cold, daily for a few days, to make sure you have the cold minimum level. After that just keep an eye on the recovery tank. I like to mark it with a magic marker. If you are loosing coolant after that then you have a leak somewhere.

regards
Mech