When to replace gas cap?

[Sidney]

How do I know when to replace the gas cap gasket or the whole gas cap for my 85 4-Runner?I mean what symptoms would have to be present to replace it.Thanks in advance.

Sidney
Repairs tv's,vcr's,home/car audio out of my home
E-mail:sidneybek@yahoo.com
Dartmouth,Nova Scotia
Canada
1985 Toyota 4-Runner,22R-E,W56,RN60LV-MSEK,rusted rear step/towing chrome bumper with 243 000 KM

[GregoryM]

Here in the states, they are frequently pressure tested as a part of the emissions testing process. If it won't hold pressure or vacuum either, for that matter, you fail the test and must correct and re-test. In practice, your vehicle will probably function normally with no cap at all but, evaporative emissions would be uncontrolled. I do not know if the gasket is available separately from the cap however, if you are still using the original unit, it probably could stand to be replaced.

[reb]

The first symptom I look for is whether it requires a key or not. There are enough vandals around, especially in the big city near where I used to live, that I always opted for a locking cap.