07 Hyundai Elantra coolant issue

[meetsum]

Hi,

Recently I bought a 07 Elantra with 100K miles on it. Since I bought the car, I noticed that the cap of the coolant reservoir tank was not properly closed. It was loosely placed on top of the reservoir mouth. Last night, just for curiosity while I was checking the coolant level, I found that it was really low (way below the minimum mark on the reservoir). I then filled the reservoir and marked the level. After that I drove that car for around 10 min. 2 hrs. Later I again checked the coolant level and found that the level dropped by about half of an inch. I also, placed a white sheet under my car to look for any visible leakage. This morning before driving the car I again checked the coolant, and found that it dropped again by another half of an inch. However, I did not see any leakage on the white sheet. I took the car to a mechanic shop and asked them to do a coolant flush. Also, asked them to do a pressure test. They said that the pressure testing was fine. By the way I never had any engine heating issues. My queries are:

1. Does the coolant get evaporated if the reservoir cap is loose while driving?
2. Is it normal that the coolant level goes down that much when the engine is cold?
3. What else could I do by myself to make sure that there is no leakage and everything is working fine?
Thanks

 

[hairystuff]

check the engine oil cap, if there is a mayo like substance in there it could be a leaky head gasket, sometimes the coolant cap can go faulty (faulty or worn pressure relief valve in cap) and vent pressure prematurely.

 

[boosted1g]

Most resiviors have seperate lines for cold and hot fluid lines.
Heat increases pressure which thus causes the fluid level to rise, thus resulting a different fluid level between hot and cold. This is completley normal.

There is also a difference between the resivior cap and the radiator cap.
The radiator is under pressure and a loose cap on it will cause lots of leakage. The resivior on the under hand is siphoned from the non-pressure part of the system and is effected by the thermostat closing to keep the coolant traped in the engine to reduce warm-up time.

 

[md1032]

I believe this vehicle has an expansion tank (as opposed to the traditional overflow tank design with check valve in the rad cap), so what you are seeing in all likelihood is air bleeding out of the system slowly over time since you were the one who originally discovered that the coolant was low. It may have been low from someone doing a flush or coolant exhange improperly and not bleeding the system properly. Continue to monitor for coolant buildup in the water pump/serpentine belt drive area, on the radiator and coolant hoses, and of course watch for white smoke coming out the tailpipe (head gasket).