05 G35 Coupe, recently drove the car home from the shop and everything seemed fine. Was in the shop to have A-Pillar gauges installed, went out the next day to drive the car and noticed some fluid had leaked from the car - appeared to be radiator fluid, radiator overflow container was empty but the radiator fluid level was fine, So I filled the overflow to the line and took it for about a 30 minute drive. Car ran fine, never overheated, no problems at all. But when I opened the hood I noticed the overflow was empty again. Check the radiator level later that day and it was fine. Repeated this scenario 3 days in a row with the same results...
Any help would be greatly appreciated

 

You're leaking coolant from somewhere, get a coolant pressure tester and find out where it's coming from.

In the mean time watch your coolant temp like a hawk when driving, it might be the coolant purge valve and when it finally goes it dumps ALL the coolant in about 20 seconds.

 

doesn't make sense that you filled the reservoir, then went for a drive and checked the reservoir and it was empty unless you have a leak in the reservoir itself...? the amount you put in the reservoir would only be drawn into the radiator after you got where you were going and then let the car cool down. but if you're getting pillar gauges you must be boosted and i don't know anything about boosted engines and blown head gaskets that might pressurize your cooling system etc. but the sequence of events from coolant present to coolant missing doesn't sound like "normal" leaking cooling system.

 

It's probably just leaking out somewhere and sucking the reservoir dry as it cools down. Only takes about 1 hour for it to cool down enough to empty the reservoir if it's that low.

Typically if you're going through that much coolant you're going to smell it though. Distinctly sweet smell of burning coolant.

 

Top off the coolant overflow reservoir. Start the car and let it idle for about 20 minutes as u keep checking for leaks.