Fuel tank vacuum

[j.maddock]

How do you remove the fuel tank rollover valve? Can it just be cleaned and replaced?

 

[GAmes]

Do you have the canister out of the tank? New canisters don't come with them. They just pop out with a little effort.

 

[petersonj]

Just recently, I have been hearing air rushing into the fuel tank when I remove the fuel filler cap on my 2002 truck. Does anyone know if the cap is vented?

- John

 

[j.maddock]

Do you have the canister out of the tank? New canisters don't come with them. They just pop out with a little effort.

I do not have it removed yet. I want the new part in hand first

 

[Chief USA]

Something you might want to ensure is not a factor is mud daubers. Those pesky insects make mud nests in just about every tiny vent and cavity. Even had one build a nest in the transmission gear case vent on my tractor which caused it to become pressurized after getting hot and push gear case oil up through the shift levers. This is the time of year those hateful bugs are building their nests.

 

[petersonj]

Does anyone know if the cap is vented?

I just answered my own question. Yes, the cap is vented and is working properly. The tank must be getting pressurized through the heat of the day and that pressure release is what I am hearing.

- John

 

[GAmes]

I suggest you read how the fuel tank & cap work in your manual. Mine has hissed since day one. It is normal.

 

[petersonj]

I suggest you read how the fuel tank & cap work in your manual.

I did check FSM before I posted. I could not find any mention about the fuel tank filler cap. It may be there, but I could not find it.

I have since looked in the "Evaporative Emissions" section and found the information.

I have owned my truck since it was new and I had never observed a release of built up air pressure when I loosened the fuel cap - until this summer. No worries, now that I know it is normal.

- John

 

[Ozymandias]

Fuel cap is not venedig.

And my truck hissed also since I owned it.

 

[Regcabguy]

Just recently, I have been hearing air rushing into the fuel tank when I remove the fuel filler cap on my 2002 truck. Does anyone know if the cap is vented?

- John

Mine did the same on my 98.5. The pump partially collapsed the tank. it was replaced under warranty. The service guy said a protective cap on the vent wasn't removed during pre-delivery. The filler neck where it connects to tbe tank wasn't tightened so I had to do that. Next my 53 block leaked. Got a new shortblock. Next the lift pump went out because it got strained by the tank fiasco.

 

[petersonj]

I thought I would share some information that could be relevant to '98.5-'02 truck owners.

I had posted earlier that I have been hearing a hissing sound each time I removed the fuel tank filler cap. As I mentioned earlier, I had never experienced this event. I have owned the truck since new and the fuel tank module was replaced under warranty in 2005 along with the VP44. It is only in the last year the hissing noise has occurred. It is definitely getting worse. I replaced the fuel filler cap with a new vented fuel filler cap. Nothing changed.

Some responses here say that it is normal, others say the vent is plugged. So, I looked into the matter further.

For my truck year, the FSM shows the following regarding the fuel filler cap. It does not specify "gas" or "diesel" and the "predetermined pressure values" are not specified, either.

The FSM also shows the following regarding the fuel tank module for my 2002 truck. The "rollover valve" is mentioned, but there is no detail of operation.

I removed the rollover valve on my truck to see how it operates. I tried blowing / sucking through the uncapped port. Air flow was blocked in both directions. I used a touch of brake clean and a small shot of air in the vent port passage. It immediately flowed freely in both directions. After clearing the vent, I observed the following:

* If I kept the rollover valve upright, air flowed freely through the vent port in both directions.
* If I inverted the rollover valve, airflow through the vent port was blocked in both directions.

I also now have a new Vulcan fuel tank module on the shelf from Geno's. The rollover valve operates exactly the same way.

I no longer have the hissing noise when removing the fuel filler cap.

- John

 

[LHastings]

Did you have to drop your tank or raise your bed to get to your overflow valve to remove it?

 

[petersonj]

Did you have to drop your tank or raise your bed to get to your overflow valve to remove it?

I did not have to drop the tank, but probably not for the reason you are thinking. I have made an easily removable (approximately 14"x14") section of the truck bed for easy access to the fuel tank module.

However, I don't think it is necessary to drop the tank to remove the rollover protection valve. The rollover protection valve is located in the forward part of the fuel tank module. There is nothing connected to it. The left side of the photo represents the front of the truck.

Mine used a wavy washer to hold it into place. To remove it, I pressed downward and simultaneously rotated the valve 90° clockwise and lifted it out. I think there are other methods to hold them in place, as well.

- John

 

[LHastings]

Thanks for the reply, but I don't want to go to that extreme. Is there room to get your hand up there to remove it.

 

[GAmes]

Is there room to get your hand up there to remove it.

If you are a contortionist with small, muscular hands....maybe. Dropping the tank isn't very difficult if you plan ahead and do it with the fuel gauge on E.

 

[LHastings]

Thanks for the info. My arm is not that small, looks like I got plan for the summer.

 

[petersonj]

Is there room to get your hand up there to remove it.

On my truck (a 2002) it can be removed without dropping the tank. I just went out to the shop and crawled under the truck and removed it and then re-installed it. My hands are not small either. Also, it is easy to see from underneath the truck.

Just out of curiosity, why do you want to remove it? It can be checked for proper operation while in place. If it is plugged, you should be able to clear the passage with it in place, as well.

- John

 

[petersonj]

@LHastings , here is a better photo with my old tank module on the bench. The first photo shows the rollover protection valve in the installed position. The nipple faces the driveshaft.

The second photo shows the valve in the ready-to-lift-out position. Note the wave spring washer.

- John

 

[LHastings]

It always had a vacuum on it when I take off the fuel cap since I got the truck new in 98. When it warm up here I'll crawl under it and see what I can find. I saw this thread and became curious about mine.

 

[Ozymandias]

Okay, it worked for 25 years just fine and now you want to wiggle these cracky old plastic just out of curiosity. I'd seriously leave it alone, there is no benefit at all for you.