Does Vented Cap Need to be Slowly Removed from Transfer Fuel Tank?

Updated 10/28/2025 | Published 03/02/2025

Question:

I am having trouble locating information on line. I have a Delta Industries 37 gallon diesel fuel transfer tank with a vented cap. I filled the tank left approximately 5 inches of air space at the top when finished filling When I went to remove the cap, on a 75 degree day, diesel fuel just came flowing out the cap. I did not, slowly turn the cap to vent first, but just pressed down and quickly removed the cap. I am hoping this was my mistake. I just believe the cap should be venting all the time to relieve pressure, but perhaps I just need to slowly turn the cap to the vent position first to prevent this overflow. Can you provide me with information and suggestions please. Perhaps my cap is faulty? Thank you

asked by: Gary W

Expert Reply:

Hey Gary, thanks for reaching out!

You will need to slowly remove the cap, like what you mentioned. Even with vented caps there can be some pressure build-up so removing the cap with some caution will help prevent your truck from becoming a science experiment gone wrong again.

Hope this helps! Let me know if you have any other questions!

expert reply by: Jon G

Jon G.

10/27/2025

Hey Gary, how did things go once you started removing the vented cap more slowly on your Delta fuel transfer tank? Did that seem to stop the overflow issue? Your update could make it easier for others dealing with the same pressure buildup.

Gary W.

10/27/2025

@JonG Jon, That was the trick! The cap we have is in fact a vented cap (I found that information during research) so removing the cap slowly is exactly what the doctor ordered. Thank you, Gary