Dear Dave,
While filling up propane at a U-Haul, I was told my LP tank certification would expire soon. Do the LP tanks on a Class C motorhome have to be recertified? —Anthony, 2015 Thor Chateau
Dear Anthony,
The propane cylinder that came standard on your Class C is classified as an American Society of Mechanical Engineers (ASME) propane tank. It is mounted to the chassis rail horizontally. Propane cylinders used on trailers are classified as Department Of Transportation (DOT) cylinders.


DOT cylinders must be recertified
According to the Code of Federal Regulations (49 CFR 180.209(e)), DOT cylinders (types 4B, 4BA, 4BW, and 4E) must be recertified 12 years after their manufacture date, and every 5 years thereafter if requalified by visual inspection. If recertification is completed using a proof pressure test, the interval extends to 10 years. The cylinder type and manufacture date are stamped on the upper collar or handle.
For more specific information, visit the Code of Federal Regulations for DOT Requalification of Propane Cylinders here.

ASME tanks do not require formal recertification
According to Manchester Tank and the RV Safety & Education Foundation (RVSEF), ASME tanks used on motorhomes are made of a thicker metal component and do not require recertification. Instead, they require visual inspection for excess rust and pitting, loose or missing brackets, and damage. DOT cylinders must also be inspected for the same issues.
Overfill prevention device
Both DOT cylinders and ASME tanks are equipped with an overfill prevention device (OPD), which prevents the cylinder from being filled beyond 80% capacity. This allows room for expansion of the LP during hot temperatures.
Since October 1, 1998, DOT cylinders have been required to include an OPD with a triangular handle. Filling stations are not permitted to refill DOT cylinders that do not have this triangular valve.

ASME tanks, however, may still have the older-style valve but have long included OPD protection and can be legally refilled.
What you experienced is common at many filling locations. Some employees misinterpret the regulations and assume that all propane containers require recertification, often using the general term “propane tank” to describe all cylinder types.
More posts from Dave on LP cylinders
- Essential LP cylinder safety tips
- Readers’ comments on refillable LP cylinders and legality of transporting them
- The ultimate guide to liquid propane (LP) systems
- How do I know when my LP tank is at 80 percent?
- I’m told my LP tank needs recertification so can’t be filled, but I’m getting conflicting advice
- Why can’t anyone fill my RV’s LP tank?!
- Twelve days of Christmas RV tools – Ninth day: hand-held LP leak detector
DAVE HAS ANSWERED MORE THAN 1,000 readers’ maintenance and repair questions. Read a directory here. There is so much to learn!
Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”
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