I believe the tank is under vacuum due to the overfill recovery system. The overflow tube goes to a charcoal canister located near the battery. The canister is also connected to a hose that goes to the intake manifold creating a vacuum. When you open the cap air rushes due to the lower pressure.

Having said that I wonder if a charcoal canister was used in 1979. A whole lot of pressure or vacuum might indicate a problem.

Hello HTTY -

If my memory is correct (50/50) it's supposed to do that. Either my 1979 245DL did that, or it was my 1975 245DL.

Has to do with the way excess fuel is returned to the tank. The FI management system on your 1979 might be the one that does it under pressure. Have you gotten any manuals? I know you have some, like Haynes, already. Check with the volvotechinfo.com site for books for your car.

Every now and then I see some on eBay, too. Skip Albright, Volvo-er for many years, had a supply for various years. I bought some. Look for screen name Skipskip.

Good Luck,
Bob

:>)

isn't the rubber line that runs through the passanger side rear (inside trunk) not only for over-flow but also a vent?

i'd have to check in the morning, but i think you may be able to access the hole for the vent at the top of the filler neck.

if it's possible, try and run some compressed air through that line.

the other thing i would suspect as faulty: gas cap.



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