Fuel Filler Cap Q?

[MikeR]

Can I ask another basic 'newbie' question please?

I want to replace the ill-fitting after-market locking fuel filler cap on my US-spec 1982 Spider 2000 FI with a non-locking type cap.

I have discovered that a generic European FIAT screw-on fuel filler cap will fit the fuel filler neck of my car. The only problem is that these caps seem to come in two types, vented or non-vented. Can anyone tell me what original type would have been fitted to an FI car, vented or non-vented?

Grateful for any responses, many thanks in advance.

[rlux4]

The cap on my '82 looks pretty original and it's non vented.
Ron

[So Cal Mark]

unless you have emission testing where the evaporative system is checked to hold pressure, I'd use the vented cap

[TulsaSpider]

Just curious Mark but what is the reasoning? Mine must be unvented cause it always releases pressure audibly when I open it.

[So Cal Mark]

there have been several threads about cars acting like they were out of gas, when the culprit was a vacuum in the tank. Since I haven't been involved in diagnosing one of those cars, I'm not sure what caused it. It may have been a malfunction in the evap system, or mods made by an owner that caused it, but the vented cap would prevent the problem

[joelbert2k]

I had a new 1970 124 sport coupe that had that issue. If I filled up the tank and got on the freeway and drove the car would cut out like it was out of gas at about 1/2 tank. If I got out and opened the cap you hear the thing sucking air in. Then I could then drive on until it was time to fill up and start over again. It wold also build up pressure on hot days when I didn't drive much. When you took the cap off then it would blow gas all over the poor attendant, no self service in those day. That cap was not vented but I sure wished it was. I took to leaving the cap loose most of the time.

I eventually found the problem. It was a three or four way valve in the evap system that was installed backwards.

[MikeR]

Many thanks!

As always, this forum turns up quality informed responses. I am very grateful for your fast replies.

Thank you again.