CNG CIVIC GX & Home Fueling
GX Fuel Filters and Fuel Tank Inspection
CNG FILTER REPLACEMENT (very expensive)
Most of the service on the GX is similar to the regular CIVIC excluding the fuel system. The CNG system requires replacement of a large low pressure filter every 10,000 miles. It cost about $122.00 for the filter excluding labor. It's the filter in the photo that looks like an oil filter. The high pressure filter is replaced every 30,000 (part cost about $52.0), also shown in the photo in front of the large filter.
The Honda Service Manual GX Supplement (available through HELM) describes how to replace the low pressure filter. The pressure is relieved by closing the manual shut-off valve, running the engine until it stops and turning the ignition switch off. The filter is removed with a wrench (in my case an oil filter wrench). The new filter is installed with a small amount of silicone grease and tightened by hand. Very simple but should not be done unless you are familiar with CNG systems and after reviewing the Service Manual.
The high pressure filter replacement (every 30,000) is a lot more work. Again the pressure needs to be relieved and the "under-floor cover needs to be removed. The filter is in a housing under the cover and it takes about an hour to remove the filter and reassemble the filter housing.
The high pressure filter inspection (every 10,000) also requires removal of the rear cover to gain access to the drain plug. The pressure must also be relieved. The drain plug is removed and reinstalled with a new o-ring and silicone grease.
My only problem with the filter servicing is the cost of the filters.
The high pressure filter is also know as a coalescing filter. I didn't remove the drain plug until 15,000 miles and nothing drained out. I think that contamination comes from dirty or warn out filling equipment. I learned to check the nozzle at commercial filling stations for oil that can pass through worn out natural gas compressors.
Fuel tank inspection
The maintenance schedule indicates a fuel tank inspection every 3 years or 36,000 miles after the production date of the tank. The fuel tank does not need to be removed for this inspection but only requires a visual inspection every 3 years or 36,000.