Saturday, November 21, 2015


While rummaging around under the chassis of our 2007 Airstream Interstate, I noticed a leak at our LP (propane) tank - it was detectable by the noise it was making.  Hopefully with this post, I can supply some information that will save other owners time and money if (or more likely when) they find that their own tanks need replacement.

You can see the leaking areas in this short video on the left side of the connection, revealed by the bubbles (I had sprayed it with soapy water for greater visibility).

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For readers who are unable to stream the video, here is a static shot of the side of the tank opposite the leaking fitting:
Heavy corrosion was visible, including exfoliation of the metal beneath the surface coating (paint).  
We decided to replace this tank outright, given the degree of corrosion that we found.  The first thing I did was contact the manufacturer Manchester Tanks (also known as "Mantank").  The information regarding the tank model (also known as "catalog number") was still visible on the tank plate shown in the photo above.
Tap to expand for greater clarity.
As the illustration above suggests, the tank that Airstream had installed in 2007 was no longer being manufactured, although it reportedly can be special-ordered as a custom fabrication that would take 6 to 8 weeks for delivery.  I didn't even ask what that price would be, but rather I began looking for a compatible stock item.  The most important parameters for this application were tank length, diameter, and configuration of the mounting brackets.  You can see from the video above just how tight the space was beneath the chassis where this tank was installed.  A tank that was even a slightly different size or configuration simply could not be made to fit.

Manchester Tank's customer service was extremely helpful and quickly emailed me their drawings for both the original #68162 and the potential replacement #6813 that I had identified (if anyone needs those PDFs, contact me via -at- gmail).  Armed with those drawings, I was able to go to my local RV repair center and ask them whether they could detect any engineering differences that would disqualify the #6813 as a substitute.  This initial part of the process is often more expensive and time-consuming - a non-DIYer owner would take their RV into a service center and let them determine what the replacement ought to be.  But that involves an extra trip plus labor charges for an initial examination of the rig and the corresponding research on their parts.  I was motivated to minimize costs for this repair, so I did that legwork myself.

Drawings laid side by side on the service counter, nobody could see any reason why the substitution could not be made, so they ordered the tank and a few days later my service appointment was scheduled.
The installation did not go as easily as I'd hoped, for the reasons described below.  
There are a couple of things that an Interstate owner needs to keep in mind for this kind of job.  First of all, Interstates in general are very rare.  During Airstream's T1N Interstate years (2004-2007), my best estimate (based on inferences from recalls and other publicly-available information) is that the number produced may have been only in the hundreds per year.  Most RV service centers have never even seen an Interstate let alone worked on one, so institutional knowledge is nonexistent.  Second of all, the Interstate isn't built like other RVs.  As a Class B, it is so small that a lot of stuff is basically piled on top of other stuff.  In order to get at a part that needs repair, it may be necessary to start pulling the vehicle apart so that it can be accessed.  The upshot is that even simple jobs may trigger relatively high labor costs.

Such was the case with this tank replacement.  Out of necessity, Airstream apparently installed the original LP tank in a rather unconventional, reverse-logic manner.  There's a tank, a mounting bracket, and a chassis, right?  So according to common expectation or paradigm, one would expect the installer to put the bracket on the chassis and then mount the tank on the bracket.  But because the work space was so incredibly restricted, what Airstream appears to have done instead is to put the tank on the bracket, cut the bolts flush, and then weld the bolts onto the bracket.  They then lifted lock, stock, and barrel up to the chassis and secured it from inside the Interstate, through the floor.  That was effective, but it wasn't intuitive, and a lot of labor was needed just to figure out how to dismount the welded-on original tank from the chassis.
It actually does, but it wasn't immediately apparent. 
 See, my original plan for cost minimization was to simply get the service personnel to put the new #6813 tank on the bracket that had been installed for the #68162, without removing the bracket.  That was the whole point behind ensuring meticulous correspondence in the specs, and it would have resulted in a quick tank swap and lower labor charges.

Alas, that efficiency was not to be, because of the welding that had been done, and because it took the service facility extra time and effort to determine that the only way to dismount the original tank was to jack up the fresh water tank inside the Interstate, and locate the LP bracket bolts beneath it.  Who knew??  It would have taken me forever to figure this out.

So for those of you facing this same situation, those are important pointers for your repair facility.  Don't let them re-invent this expensive wheel.  My total cost was about $550 for the tank and $720 for the labor.

Here are a few shots of the new tank as installed.  
Forward end.  The orange thing at photo bottom behind the tank is the running board ("ground effects") on the starboard side of the vehicle. 
Aft end.  The only visible difference with this tank is that the emergency vent is in a lower position (copper line at bottom).  I could have done without yet another appurtenance that causes potential ground clearance issues, but it's not as low as the engine tailpipe, which is that diagonal feature in the lower right corner of the photo (that's its protective shield).  

I don't know why the original LP tank rusted out so badly and in such a short period of time.  I have the original purchase and maintenance records for this Interstate, and there was nothing in that documentation, nor was there any physical evidence, that this vehicle was subjected to unusual operating conditions.  It was reportedly bought by a newly-retired gentleman and his wife in the Midwest and kept primarily in the Midwest.  It was driven only lightly, an average of about 3,500 miles per year.

This kind of premature rust is a potentially treacherous problem for RV owners because it is so unexpected that they might not think to check for it.  I have extended family members who have house-servicing propane tanks in their back yards that have been directly exposed to the elements for decades and still show only the barest surficial corrosion, certainly nothing structural and certainly nothing that would cause leaks.  I myself own a portable BBQ tank which is spotless after a lifetime of sitting outside in full subtropical weather exposure.
I can't even remember how old this thing is, or how many years it has been sitting outside, and look at it.  It's still in perfect condition.  
Everything in my life experience up until this incident said, “Propane tanks are properly designed for outdoor use, and they last a very long time”.  For that reason, I never thought to evaluate our tank until I heard a funny noise underneath the Interstate.

I don't have an answer for this one.  All I know is that propane leaks will not improve on their own - they will only get worse, and they could do so with catastrophic consequences.  So this is something for which every RV owner should remain on the lookout.

Further discussion and commentary can be found on this Air Forums thread.

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