This situation is more complicated. With the vehicle running, especially if it has been running for more than 15 minutes, I agree that there is no possibility of developing pressure in the tank.

The pressure is developed when the vehicle is not running. The tank pressure is slowly equalized from the vacuum that had developed when it was running, and, the air above the fuel expands with temperature rise to create pressure in the tank. It does not happen often, Navy, but, trust me, it does occur.

Man I hate to think how hot it would have to be outside the car for this to happen, let alone happen very quickly. I've been in a couple of the hottest places on earth and never saw this happen, but nothing is impossible.

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'10 Chrysler T&C Stow-N-Go White. Grandpa's ride.

'13 Chrysler 200 Touring Candy Red. Grandma's ride.

Age and cunning will always over come youth and vigor.

The small hole underneath the fill cap is an overflow hole for draining excess fuel spillage when fueling. The tank vent exits the top of the tank as a hard line, runs down the rear of the tank and exits underneath along side the fuel supply line. It has a short rubber section there and hooks to another hard line section that heads to the left side of the car and turns down right in front of the left rear control arm/subframe mount. This is all on a W123 model. I am not sure if the W124 is the same or if the vent is different or not. Check to see if it has a vented cap instead.

It does not need to be all that hot. If the vent is reasonably well sealed, a small rise in temperature would develop pressure in the tank if the vehicle is not running.

You have been in a couple of the hottest places on earth and never saw this happen because your vent is not clogged.

Yup, I was confused with my old Nissan truck. Darn dirt dobbers are bad about building mud nest is the worst places. I did run the speedo cable I have in the garage down the drain hole after the first time I overflowed the damn tank. Well actually I kept putting some diesel in the hole to help soften the crap, then I put the cable in the electric drill and finally cleared the drain. The mistake I made was failing to us a catch bucket under the tube and made a mess on the garage floor.

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'10 Chrysler T&C Stow-N-Go White. Grandpa's ride.

'13 Chrysler 200 Touring Candy Red. Grandma's ride.

Age and cunning will always over come youth and vigor.

Pretty sharp arn't you.

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'10 Chrysler T&C Stow-N-Go White. Grandpa's ride.

'13 Chrysler 200 Touring Candy Red. Grandma's ride.

Age and cunning will always over come youth and vigor.

Just an engineer, Navy, no more and no less.

Thanks guys for all the replys I didn't mean to start a war.
Let me be sure I have this straight the vent line is under the car and must be cleaned from there.
The overflow line is at the top of the fuel neck and may be cleaned from there.
If you don't have a speedo cable what can you use?

Pay no attention to Navy and myself. We go back a long way. I love to correct him when he is wrong.

Me wrong!!! Never... don't you be silly now.

__________________
'10 Chrysler T&C Stow-N-Go White. Grandpa's ride.

'13 Chrysler 200 Touring Candy Red. Grandma's ride.

Age and cunning will always over come youth and vigor.

?so what do I use and how?

Coat hanger, bicyle brake cable's, electrian's fish wire, and anything else of such a nature.

__________________
'10 Chrysler T&C Stow-N-Go White. Grandpa's ride.

'13 Chrysler 200 Touring Candy Red. Grandma's ride.

Age and cunning will always over come youth and vigor.