I have owned alot of older cars - mostly AMC. I purchased a 79 Olds Cutlass Calais. It runs perfect but when I went to the gas station to put gas in and when I unscrewed the gas cap there was an unreal amount of air pressure that blew out around when unscrewing cap. It was alot. Never seen anything like that. The car runs great. Is it dangerous? Should I have concerns? Thanks for anyones help, Oldsmobiles are Greek to me.

 

No it's normal. In the owners manual it usually reads to open cap slowly because of this. Gas expands and contracts with temperature, on a very hot day, there will be quite a bit of pressure in there.

 

Not sure I agree with this. I can't speak for 1979 in particular, but it's common practice for the gas tank to be vented. I would expect to see at least one hose running to a charcoal canister in the engine compartment. Anyone know for sure?