I currently own a 1983 Chrylser Fifth Avenue that has approximately 127,500 miles on it. When the temperature outside gets between 90-100 degrees it tends to vapor lock. It doesn't matter whether I use high grade gas or not. I know that road heat can play a factor in it also. When it is 100 degrees outside the road heat can make it seem like it is 125 degrees outside. How the heck can I stop it from vapor locking. It is getting old. The car has an Eight cylinder 318 automatic engine. It only seems to vapor lock when it is hot, even with a full tank of gas. Help! I change the oil every three thousand miles and have replaced the fuel pump and filter in the last yr. It has probaly been two years since it has had a tune-up, other than me changing the spark plugs.