Leaking Onan Generator Fuel Filter
I learned something recently about Onan generator fuel filters — sometimes they leak!
After changing the oil, oil filter, and air filter on my Onan generator, a ran it for a bit with the cover off to make sure the oil filter wasn't leaking. (Note that you should never run your generator for very long with the cover off because it interferes with the cooling). The oil filter wasn't leaking, but I noticed gasoline a the top of the rubber fuel line going to the carburetor. At first, I though it was a leak in the fuel line or a loose clamp, but after checking the fuel line for cracks and tightening the clamp, I put a piece of towel paper up against the body of the filter itself and it rapidly got wet with gas.
After a little Googling, I learned that this is a common problem. The fuel filter has a seam near the top, and since it's after the fuel pump, the excess pressure will sometimes cause a leak there. Having pressurized gasoline spraying around the inside of your generator is definitely a bad thing.
My generator has two fuel filters, one just below the carburetor, and another down below, just ahead of the fuel pump. They are identical (at least on my rig), and you don't really need two of them. The lower one, ahead of the fuel pump, is less likely to leak because the gas is under less pressure there, but it can still go bad. Onan recommends replacing the upper filter with an adapter that basically just a metal tube with threads on one end and a nipple for the gas line on the other end, so it can't leak. They also recommend replacing the lower fuel filter with one that has a different design.
The parts shown here are the replacement parts for my particular Onan generator (Model HGJAB) and also fit models HGJAA, HGLAA, and HGLA. They are common to many Onan RV generators, but make sure they are right for your unit before purchasing them. If you have a filter or filters like the old filter shown below, it's likely that they should be replaced as soon as possible.
Here are some pictures of the adapter and the old and new filters:
Old Upper Filter
Old Lower Filter
New Filter (replaces lower filter)
Adapter (replaces upper filter)
Where to Get the Parts
I found the new filter (part # 149-2341-01) at Amazon:
The adapter (part # A029S253 or A026E529) was a little more difficult to find. Amazon had a listing, but they were out of stock. This search, though, turned up a number of them. I bought mine from eBay.
Here are the two parts you need:
Replacing the Upper Filter
This is not a very difficult job. I removed the air-filter housing, but that was a bit tricky and I don't think it's necessary. I've included the steps for that, but you can probably skip them. Removing the filter housing still didn't let me get a wrench on the filter, though if you have a 15/16 or 25mm flare nut wrench, that might (or might not) work. I used a pair of water pump pliers on the filter body. Normally, this could damage the filter, but since I was throwing it away, I didn't care. See the pictures below for details.
- Disconnect the shore power. If you want to be safe, disconnect both the chassis and hours batteries as well, especially if you remove the air-filter housing. It's very easy to hit the start button on the generator with your arm while working the housing in and out.
- Remove the generator cover by pulling the top toward you, then lifting up and out.
- With a screwdriver or small nut driver, loosen the clamp at the top of the black rubber fuel line and slide it down about 3 inches.
- Be sure to wear protective goggles and put a rag around the fuel line where it connects to the filter — the fuel may be under pressure, especially if your fuel filter wasn't leaking, and could spray into your eyes.
- Pull off the black rubber fuel line (pull down). Rotating it back and forth may help.
- (Optional — See the steps below for removing air-filter housing.
- Using a pair of pliers, unscrew the filter below the carburetor and remove it.
- Remove the plastic cap from the new adapter. If one of your filters is not leaking, you can put the plastic cap on it to protect the threads and save it for use in emergencies.
- Screw in the adapter and snug it up with a 14mm or 9/16 wrench (14mm is the correct size, but 9/16 will work).
- Slide the black rubber fuel line onto the nipple at the bottom of the adapter.
- Slide up the clamp and tighten it.
Removing and replacing the air-filter housing (optional)
- loosen the three silver clamps holding the housing cover by pulling out on them.
- Pull out on the bottom of the cover, then down to remove it.
- Remove the air filter by pulling it out.
- Remove the two silver bolts and the two black nuts next to the carburetor throat. Put them somewhere safe.
- The housing is still attached (sort of) by the black rubber tubes at the top center (intake tube) and the bigger one at the bottom left (exhaust tube).
- Work the housing down and out at the top (it's a tight fit, but it will come out), then lift it out of the lower rubber tube. Be careful and patient so that you don't damage the housing or the bolts near the carburetor throat.
- When replacing the housing, put the top in first, making sure the rubber tube at the top is connected. You can reach around the back to connect it.
- Once the top is in and on the bolts, seriously deform the lower rubber tube receptacle to get the bottom in. Do this with your fingers. Using a tool might cut the rubber.
Replacing the Lower Filter
Be careful, significantly more gas will flow out here, though it won't be under pressure. Be ready with something to plug up the gas line. I used a tapered nail set. I think a golf tee might work as well or better. The filter is under the generator just ahead of the fuel pump (follow the black rubber gas line down from the fuel tank), and should look like the one above by the carburetor. If there's no filter there, you'll have to figure out a way to add one.
- Loosen the clamp where the black rubber fuel line connects to the filter. Since you're down there, you might want to replace the fuel line as well, but be prepared to stop gas from flowing from the tank.
- Slide the clamp back up the fuel line.
- Pull the fuel line off the filter. Be careful — gas will come out — keep your face well away and wear protective goggles. Be prepared to plug the line with something.
- Put a wrench on the nut at the end of the fuel pump so it doesn't turn. With a second wrench or pliers on the hexagonal part of the old filter, unscrew it.
- Screw in the new filter, again using a wrench or pliers on the hexagonal part, not the body.
- Attach the fuel line to the filter.
- Slide the clamp back into place and tighten it.
Make sure everything is in place. If you removed the air-filter housing, make sure the intake and exhaust tubes are attached. Replace the air filter and its cover, making sure all three clamps are shut. Reconnect the batteries and shore power. Start and run the generator for about a minute with the big cover off to make sure there are no leaks. You may have to start it a few times before all the air is out of the lines. Put the cover back on, but first, note where the upper catches connect on the back of the cover. Insert the lower edge first, slide it to the right, push in the top, and bang on the cover with your fist over the two upper catches. One is near the ":O" in Onan. The other is in a similar spot on the right. Make sure the cover is on tight!
Congratulate yourself on a job well done!
Here are some more photos from the job:
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— Bob Ray