Vacume in fuel tank

[DavidGardner]

Some times when I run my fuel tank down to where the fuel warning light comes on I get a definet whooshing sound when I loosen the fuel filler cap. Is this normal? I am concernd that if there is a vacume in the fuel tank this might be hard on my fuel pump or lift pump. Any thoughts on this?

 

[RedRamer]

Every time I fill up, either at 1/2 way mark or lower, there is always a vacuum in the tank. Normal, I'm sure.

If the vacuum is such that you have a huge sucking sound when taking the cap off, you might need a new cap cause the cap probably sets the vacuum pressure.

 

[Cooker]

I was/am just going through this myself.



Check this out: http://dodgeram.org/tech/dsl/ISB/low_power.htm Maybe if you are lucky, this will solve your problem.



If not, what it seemed to come down to in the last thread was that some feel that it is normal and a little vaccume is ok. IMO It may be ok to have a little vaccume, but on my truck I'd rather not have any.



If the fuel vent cap doesn't fix the problem, the next likely culprit is the rollover valve isn't working properly.



-Ryan

 

[RedRamer]

Well chew my gotchies... If that's what my vent is suppoed to look like, then what the heck am I doing with vacuum?

I'll have to get down and dirty tonight.

thanks

 

[illflem]

You will always have a little vacuum or pressure in your tank, that's the way it's designed. You know you truly have a problem if your tank collapses, it has happened to a few folks.

 

[Cooker]

Here is what too much vaccume will do to your fuel tank.



I still haven't found the root of the problem. I suspect it is the rollover valve and from what I understand (maybe I'm worng) the only way to replace it is to buy a new fuel tank sending unit.

 

[Cooker]

Like I said, I suspect the rollover valve may be bad. Is the rollover valve the same as the fuel check valve? It seems to me they are the same, but I'm just double checking.



I have found out the fuel check valve is a separate part number and is replaceable on it's own. hopefully they are the same thing with different terminology. I'll try a replacement check valve, hopefully DC doesn't want me to give blood for the damn thing, and maybe I'll get lucky and it will solve my problem.



-Ryan

 

[John]

????????

I believe the TSB for the rollover valve only pertains to '98. 5 24v Rams. The first ones sent from the factory still had the red cap installed from the tank vendor and it seemed to slip by the factory installers. Mine was removed and tossed in the bed of my Ram by the dealer when performing the pre-delivery prep. I can't ever remember removing the fuel cap on my '98. 5 24v and experiencing a vacuum situation (like you would with a gasser). The rollover valve (if uncapped) should eliminate any vacuum in the tank... it sure does on mine.

 

[AJMezera]

After replacing the tank twice and being informed

about the "little red cap", I still had to remove the cap myself on my 98. 5.

 

[RedRamer]

Cooker... where do you get the nice diagrams?

 

[Cooker]

I pulled that pic from Dave Fritz'z website: http://dodgeram.org



My scanner and digital camera come in handy for any other pics I might need.



-Ryan

 

[Cooker]

Finally fixed it!

I replaced my rollover valve last week and now have gone through a full tank of fuel, no more woosh of or when I remove the fuel cap



With the old rollover valve removed I "tested" the new and old one by blow air in in the vent and then trying to suck air out of the vent. Both would allow me to suck air out of them, but the old valve would not allow me to push air into it, and the new one would.



This reaffirms my suspecion (not to mention the damaged fuel tank) that vaccume was building up within the tank)



The truck does seem to idle a little smoother (it could possibly be just in my mind because I wanted it to run better ), and I will average a few tanks to wait to see if there was any fuel mileage gained.



I'm very happy I finally found the root of the problem, and I now feel that a little vaccume is not normal.



A special thanks to Evan Beck who recommended the idea of replacing the rollover valve.



It is a very easy repair, maybe 10 min tops, and the part numbers are: Rollover valve #52127666 and Gasket #4002149 Parts totaled $23



I hope this might help some others who are experiencing this problem.



-Ryan

 

[JMarkos]

After my Dads 98 got it's 2nd tank put in ( by dealer under extended waranty, with no real fix)because of colapsing I saw the above info. His had the cap, we removed it and the problem was solved.

 

[pwr2tow]

There is also a spring loaded valve inside the fuel filler cap, I took a pen and wiggled it back and forth a little and pushed it in and out, that solved the problem for me and at zero cost

Ron.

 

[Evan A. Beck]

Ryan, glad I could help!



I had the same thing happen on my 98. 5 24V, and I had to have the tank replaced. Glad it was under warranty!

 

[Cooker]

ronsram1999,



Maybe the fuel cap does vent a little, but if it vents enough, why was there such a problem with the little red caps on the rollover valve? Just a thought.



I guess one could try a new cap first (or try to repair it as mentioned), and if that doesn't solve the problem then rollover valve it is.



-Ryan

 

[pwr2tow]

cooker, I don't have the answer all I know is I had the same problem last winter and started a post about it. I crawled under truck and checked roll over valve, no cap, I then done the spring thing in filler cap and have never had a problem since. Maybe the spring has too much tension when new. I would say though that if the vacum is causeing collapsed tanks then there is definatly something wrong with the roll over valve in tank and the cap vent spring. If the tank just vents when opened then the cap vent spring has too much tension. Just my observation, but it worked for me.

Ron