I just had the thermostat changed, and had not driven it since (few days) I checked the water tank and it seemed lower that it should be. So I gave it a test drive to get the water hot, then took the lid off and water was boiling and overflowed. Is this normal?
2Can you add vehicle information? Year/make/model/engine?– Pᴀᴜʟsᴛᴇʀ2 ♦Sep 5, 2016 at 9:13
A couple of things: 1) be very careful removing the pressure cap on a hot engine, the coolant is under pressure and may be above its boiling point at atmospheric pressure, this means that it can start boiling as soon as you open the cap – the resulting steam and geyser of hot water can cause bad burns; 2) because of 1, I'm wondering if the coolant was boiling before you opened the cap, or if it started when the pressure dropped; and 3) as @Orb pointed out if the cooling system wasn't fully bled and topped off after the thermostat change the coolant level may have dropped as you drove home.– dluSep 5, 2016 at 12:47
Assuming there are no other issues with the cooling system it could be that the coolant system wasn't bled fully following the thermostats replacement.