Drove around with radiator fill cap not fasten

[Jimmie]

I drove around for two days with the radiator fill cap not fasten and my CEL came on. When I noticed it I also noticed that my temp gauge was flat. No fluid came out or anything nut now I have a CEL and the temp gauge is acting funny. When I start up let the car get to temp the gauge starts to rise normally, but after about 3-4 minutes it falls flat. A bout 2-3 minutes later the gauge rises to normal temp then falls flat again and stays there until I start her up again. the car is running normal, no hesitation or anything. Help

 

[joegr]

You probably have air in the cooling system now, and need to properly refill and bleed it. There may be hot spots in the engine now that could lead to damage.

 

[Rodney Dangerfield]

Yes, if you don't have the coolant system properly serviced you can very easily cause damage like blowing the head gasket. Have your car towed to your mechanic and have them look it over before you drive it or even turn it on again.