Occasional Faint Fuel Smell @ Engine and at Rear Axle Area

[ed1948]

My 86 MCSS (90K miles)that I've driven only a few months - all lines well oil/grease coated, virtually no rust on chassis or underbody components.
-sometimes there is a fuel smell once the engine is shut off and occasionally even on a cold underhood
-during the 6 months of non driven time the gas tank volume dropped by a third
-today I was adjusting the muffler hanger and could occasionally smell fuel
-there are no drips, gas tank flanges are dry, lines have no drips, visible parts of gas tank look very good with 0 rust
-gas cap is tight and charcoal canister connections are good and the 2 rubber hoses are firm and not cracked
-can't really smell any fumes when opening the garage

I (hope correctly) that underhood fuel fumes are to be expected.
I'm wondering how secure the fuel system components are at the tank? I have a rough idea of how the fuel fume recovery system works.

Is there some method a backyard mechanic to use to check for gas or gas fumes leak without lowering the tank?(please no lit match ideas) Presently the tank is near full. Any common areas of failure after several decades?

 

[fleming442]

My Bonneville had rust pinholes on the top of the tank near the sending unit. Some genius at GM thought it would be a good idea to puta foam separator around the lines up there....

 

[ed1948]

If I plugged the canister rubber line and try to pressurize the tank(apply compressed air to filler through a rubber sealing gasket) What should happen? I assume if the vent line is blocked and the tank is non holey, pressure should build and hold in the tank. I'm fairly certain that normal rustproofing methods would not cover the tank top area where the foam separator is.

 

[406 Monte]

I would think with no holes it should build pressure and if there is a hole you should find it. Obviously I know 😱 Lol

 

[axisg]

I would be looking at your fuel tank cap. It may no be sealing and venting to the atmosphere ( explaining your fuel loss over the winter )

 

[axisg]

regarding the Fuel Smell maybe the 30 year old charcoal has absorbed all the fumes it can and need replacing ( like mine ). I have read where you rebuild your own or find something newer at the wreckers

 

[ed1948]

I just(don't laugh) did the suck blow test on the cap. It leaks on vacuum but holds on pressure. - normal. There were no smells around filler and no smell in the garage just now.

 

[axisg]

It could leaking fumes be past the seal on the gas cap or anywhere along the vent line

 

[pontiacgp]

if the car sat for 6 months and lost 1/3 of the fuel then the gas tank must be leaking. The pick up and the lines are at the top pf the tank so if the car was sitting no fuel would be leaking from the lines.

 

[ed1948]

A follow up..
-no gas smell lately but there is a smell of old gas coming from the charcoal canister.--time to rebuild it