The stories about fix-a-flat have been raised to the level of urban legend. There are many reasons for this and chief among them are that auto service facilities have an ax to grind with the product. Fix-A-Flat reduces the need for road service and creates a need to clean the inside of the tire prior to repairing it.
But the complaint that seems to dog the product the most is the insistence in some circles that there is a danger of explosion in repairing a tire that has been treated with fix-a-flat. At one time the propellant on many fix-a-flat type products was flammable.
I know this because I was around doing this job back when it was a hazard. Part of the accepted repair process at the time was to ream out the puncture hole with a barbed probe; the threat was that a spark created as the probe contacted the steel cord in the tire would ignite the flammable vapor present from the fix-a-flat and cause an explosion. This was corrected a very long time ago when manufacturers switched to non-flammable propellants.
Fix-A-Flat is one of those products whose trade name has become the popular name for a product that performs a certain task, similar to Xerox being synonymous with photocopying. So there are many manufacturers of fix-a-flat type products. SOPUS products, which is affiliated with the Shell Oil Company, makes Fix-A-Flat and has posted a demo of how the product works.
In the demo the contents of the aerosol can turns into foam and then, after about two hours, returns to a liquid. They state that in either condition it cannot hurt the tire or the TPMS sensor and does not create false readings. They do admit that there will be some liquid remaining in the tire which will have to be cleaned out.
Some of the problem with the product’s reputation may not be its own fault. Consumers have been known to use multiple cans of fix-a-flat when faced with the prospect of changing the tire on the road, calling for roadside assistance or risking a replacement as they drive on a poorly inflated tire. All this adds to the anecdotes that service professionals relate about the sealant as they cope with the consumer’s misuse of the product.
Chat traffic about fix-a-flat’s compatibility with TPMS systems is a mixed bag. Some entries indicate that it is not a problem if the sensor is cleaned properly, while others cite owner’s manuals that specifically recommend against using “tire sealant products”. Some of the problem may be aggressive sales tactics by service facilities, which are using evidence of fix-a-flat as an excuse to sell a sensor, but the owners’ manual may be a good place to start before you buy that can for use in an emergency.
The SOPUS product (Fix-A-Flat) does prominently display in all of its advertising and on the can itself “Tire Sensor Safe”. I have not seen a TPMS sensor malfunction as a result of using the product, but the demo did not convince me that damage would not occur since radio signals are used to tell the low tire light to come on. It seems to me that the liquid residue could interfere with the sensor’s ability to transmit the signal. So the fix-a-flat debate continues.